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    • Help! How do I manage my commercial oyster nursery?by Coline Arqué, Marylou Pourret and Robin Thibault

      Published by Charlotte Recapet the September 6, 2021 on 4:16 PM

      Evaluation of food limitations in commercial oyster nurseries: an aid for managers

      Oyster production provides an important number of ecosystem services (nutrient cycling, providing habitat for other marine species, ...). Furthermore, shellfish farming is promoted and recognized as providing social and economic benefits, as well as ecological benefits. Oyster growth and production depends on several factors such as temperature, salinity, freshwater flow/rainfall, current speed, density, feed concentration and phytoplankton species composition, feed sharing with other species and disease outbreaks. For this reason, modeling can be useful in understanding the feedback between agricultural and environmental systems and the effects on production. Mass balance models can help estimate the food requirements of a given spat stock.

      Objectives:

      • Develop and evaluate model for different culture structures using Pacific oyster spat
      • Make the model available online for wider use
      • Ensure it tackles two questions that arise when planning or managing an oyster nursery: how much food is required to sustain a given stock and for a typical range of food available in the surrounding environment, what is the maximum biomass that can be stocked

      Why use the Pacific oyster?

      • Strong Economic Interest: 4.4 million tons in 2003 (FAO)
      • The cultivation is well suited: to small family businesses, cooperatives or regional industry
      • The grow-out phase can be carried out by: relatively unskilled labor with minor investment in equipment and infrastructure

       

       

       

      The overall goal of this model is to estimate the food inputs for a given stock biomass; and the maximum stock biomass for a given external food concentration.

      Different parameters were considered in this model relied on the experiences of Langton and McKay (1976) ...

      Level of food supply

      Simulations of two feeding levels with an interval of 6 hours:

      • Exp A : Exp A: daily intake of 180 algae cells/μL x 250 L of tank
      • Exp B: 120 algae cells/μL x 250 L of tank

      In addition, to mimic the experimental setting, the model application includes only one class of oysters, so that at each run of the model, the spat size is set to the same size obtained from the weekly observations of Langton and McKay (1976) for the 6:00/6:00 regime.

      [Food]Nursery

      Key parameter used in the model as the optimal concentration to be maintained in the production unit. [Food]nursery: minimum dietary concentration that maximizes intake OR optimal concentration for growth.

      Temperature

      Chosen according to other references on the subject. The temperature for the maximum clearance rate is approximately 19°C. Thus, the lower limit of the model is set at 4°C and the upper limit at 30°C.

      The biomass of the stock was calculated by considering the density of 50 spat per liter, multiplied by the volume of the tank (250 L) and by the size of the seeds.


      Conceptual model for the oyster nursery.

      The choice of a model that takes several parameters into account allows a rendering close to reality. This application is a useful tool for managers who can limit as much as possible the costs that are not essential for the good development of a species. Indeed, the aquaculture environment is a field with high socioeconomic stakes. Therefore, it is useful in the long term to find new management concepts for sustainable resource management.

      RESULTS

      Week 0

      Week 2

      Week 3

      Following weeks

      Exp A

      Exp B

      Exp A

      Exp B

      Exp A

      Exp B

       

      Feed supplied is much higher than the stock requirements

      Feed level supplied is still enough

      Oysters are fed less than the optimum

      Feed level supplied is near the threshold

      Feed level supplied does not meet the needs of oysters

      lower spat weight for experiment B than for experiment A

      These different growth rates measured in Exp A and B (Langton & McKay 1976) confirm the model's predictions of dietary limitation. The results of the model are also consistent with those of Langton and McKay (1976), which predicted that oyster spat are not diet-restricted during the first two weeks. The model outputs provide the feed requirements to ensure minimum concentration in the nursery. It also gives the maximum biomass that can be stored to ensure a minimum concentration in the nursery for optimized growth.

      ASSISTANCE TO MANAGERS

      In order to promote widespread use, the model described in this paper for Pacific oyster nurseries is made available online: http://seaplusplus4.com/oysterspatbud.html. It allows to carry out simulations on several types of nursery systems.

      This work describes the model user interface, including the menus for nursery setup (and seed characteristics), output for food requirements, output for optimum stock, and advanced settings (allows the user to modify the optimal feed concentration for oyster filtration). Examples on how to use the model for different case studies are also provided.

      Model limitations include the following:

      • Important effects that occur at smaller scale are not simulated in the model, e.g., changes in the water flow rate due to oyster size/densities or tank shape
      • The option with bloom tanks assumes these are interconnected with the oyster-holding tank, which together are the simulated unit. In this case, the water flow is the water that enters from the outside (an adjacent ecosystem for instance) into the bloom tanks forced by tidal height or pumped
      • The salinity effects on filtration rate are not simulated and thus it is assumed that water salinity is higher than 20

      MODEL APPLICATION TO FARMS

      In spite of the model simplification, it can still provide guidance for managing stock and food limitation in natural feeding oyster nurseries. It offers a wide range of possible scenarios in which the nursery operates. It provides guidance for the management of stocks and food limitation in naturally fed oyster nurseries. In addition, it also allows a quantification of the general rules concerning the spat holding capacity for a given nursery. Finally, the total biomass stock that can be maintained will depend on the quality of the spat.

      The cost of producing a species like oyster for commercial purposes needs to be limited. The technique applied in this paper to get there is sound for oyster farmers. It is important to know all the biological and ecological aspects related to the good development of this species. The food aspect is a primordial resource in the growth of a species. Therefore, the model proposed in this study is useful to better understand what the essential nutrient inputs for the good development of the oyster are. However, there are many factors influencing the growth of these organisms and further study to refine the model may be required.

      TO CONCLUDE …

      The model:

      • Presented provides an assessment of the seed stock limitations in an extensive commercial oyster nursery that can function with respect to food limitation.
      • Provide valid indications on the limits of the maximum stock in a given nursery or on the food requirements of a given spat stock for optimal rearing conditions.
      • Is intended for managers of commercial operations and can be used online.
      • Can be developed based on feedback from the growers regarding its usefulness.

      In addition, other features they consider important could be included, as well as other oyster species. We can also apply it on other biological models with a strong economic interest and whose physiology of the species is suitable for study in a controlled environment.

      This model is applicable to species whose production cycle can be controlled. Indeed, the model studied is a tool that tells us the maximum amount of food necessary for the proper development of the species. Therefore, it cannot be adapted to species that cannot be analyzed in a closed and controlled space. It should be noted that linking statistics to biology is a fundamental approach to evaluate and understand a species in the best possible way while including other parameters that may have a negative or positive effect on it. Furthermore, it would be interesting to extend this study to other oyster species and other organisms concerned by these culture systems. In addition, as the authors say, it would be interesting to consider the opinion, yields of shellfish farmers in order to improve the model for a better management aid.

      Read the full study: Nobre A. M., Soares F., Ferreira J. G. (2017) A Mass Balance Model to Assess Food Limitation in Commercial Oyster Nurseries. Journal of Shellfish Research, 36(3), 738-748. https://doi.org/10.2983/035.036.0323

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    • How raising snails allows to better understand the dynamics of a parasite?by Thomas Boyer and Thibault Dindart

      Published by Charlotte Recapet the July 19, 2021 on 9:38 AM

      The analysis of epidemiological dynamics depends on host and parasite interactions. But these interactions fluctuate because hosts and parasites are heterogeneous entities that exist in dynamic environments. Resource availability is a powerful environmental constraint of intra-host infection dynamics (temporal patterns of growth, reproduction, parasite production and survival).

      In this study, researchers developed, parameterized and validated an explicit resource infection dynamics model by incorporating a parasitism module in the energy balance theory. The mechanisms explained are the multivariate dynamic responses of the human parasite Schistosoma mansoni and its intermediate host snail to resource variation and host density. This parasite is widespread in Africa and inter-tropical America. Worldwide, more than 200 million people are infected with it, 9 million suffering from its symptoms, which cause more than 200,000 deaths every year. It tends to have erratic localizations (liver, spleen) and the accumulation in these organs of lost eggs makes the severity of the infection.
      The most common symptoms are diarrhea and even dysentery. Complications can appear such as rectal prolapse, fistulas, occlusion, appendicitis.

      To do this, they have parameterized the model using an experiment that manipulates food resources and follows the growth, reproduction, parasite production and survival of snail hosts. The model is then validated by simulating the dynamics of infection for host individuals undergoing different levels of intraspecific competition and comparing these predictions with the results of another experiment that manipulated host and resource density, and hence the intensity of resource competition

      This bioenergy perspective suggests that variation in resource availability and competition could explain the infective dynamics of this parasite. To begin with, total cercaria production could be low when snail densities are low (because there are few infected snails) or when snail densities are high (if competition limits per capita parasite production). This potential relationship between snail density and the risk of human exposure could be the reason for the success or failure of current and proposed methods of schistosome control, which depend on reducing the density of snail vectors by molluscicides or predators. If resource competition in natural snail populations is strong enough, then snail reduction programmes could backfire, as reducing intermediate host densities could free the remaining hosts from resource competition, thereby increasing parasite production rates per host.

      To conclude this bio-energetic model seems to indicate that the fight against the parasite Schistosoma mansoni begins with the regulation of snail populations (first host of the cycle). In order to better regulate this infectious dynamics, measures must be taken collectively between the countries concerned and must be directed towards a total reduction of snails or a limitation by intra-species competition. This model would establish priority levels of parasite infection for certain areas and would be followed by measures to control the parasite. A first measure would be the installation of pipelines to prevent the release of infected faeces into watercourses.

      Read the full study: Civitello, D.J., Fatima, H., Johnson, L.R., Nisbet, R.M. and Rohr, J.R. (2018), Bioenergetic theory predicts infection dynamics of human schistosomes in intermediate host snails across ecological gradients. Ecol Lett, 21: 692-701. https://doi.org/10.1111/ele.12937

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    • Water, a limiting factor in lizard activities and distributionby Alice Loubet-Laouina

      Published by Charlotte Recapet the June 28, 2021 on 3:32 PM

      Water is an increasingly scarce resource for us, so we can ask ourselves: When will it be for animals? How will they react: flee, adapt, evolve?

      Predicting the effects of climate change on biodiversity is an ecological objective in conservation management. Here we are interested in water restriction role on activities and distribution on ectotherms with the mechanistic niche model.

      Who am I


      Photograph by Olivier Cardona, 2013
      My name is Tiliqua rugosa or Sleepy lizard.

      I am an ectotherm. I explain: I don't produce heat, so I need the sun to warm me up.

      I live in Australia.

      I measure 40 to 45 mm.

      I live for 50 years in the wild!

      I love to eat flowers, fruits, and the leaves of annual plants.

      I can lose more than 70% of my body water despite being adapted to the desert.

      What is a mechanistic niche model?

      So, the study scientists use this model with environmental and biological data of the Tiliqua rugosa. These data create Microclimate and Animal models. This allows us to understand how climate change affected species with a complex life cycle. This model makes it possible to make predictions on the distribution of animals. The same scientists used this method for another study (Enriquez-Urzelai et al. 2019).

      Biological activities

      When we talk about the biological cycle, we are talking about growth and reproduction activities. These activities require energy. Organisms have to make a trade-off between spending and storing energy.

      The consequences of water restriction

      When lizards only have access to water through their food or rainfall, their activities are reduced to the maximum to limit their dehydration and keep their energy. So Sleepy lizards hide in their burrows. They nest in a burrow up to 60 cm deep.

      Water is a limiting factor in reproduction. According to two simulations, lizards reproduce little in the center and northeast of Australia.


      Estimation of net reproductive rate

      Climate change

      To predict long-term evolution, we can use general circulation models in combination with mechanistic niche models. Therefore, it is interesting to compare different scenarios. Scenarios of the general circulation model1 can complement our niche model.

      For the most part, water restriction is not a limiting factor for lizards. By running six scenarios under the assumption of water restriction, we find that the reproduction rate remains constant within the current ranges. The ACCESS 1.3 and GDFLCM3 Scenarios are exceptions.


      Estimation of different scenarios

      Species will be affected by climate change because it will depend on future precipitation patterns. Global warming could therefore cause increased dehydration regardless of rainfall variations.

      1 General circulation model: statistics of several environmental factors allowing to make predictions according to different scenarios developed by countries.

      Read the full study: Kearney, M.R., Munns, S.L., Moore, D., Malishev, M. and Bull, C.M. (2018). Field tests of a general ectotherm niche model show how water can limit lizard activity and distribution. Ecol Monogr, 88: 672-693. https://doi.org/10.1002/ecm.1326

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    • Does food quality increases moult organism vulnerability to pollutant impacts? by Charlotte Couedel, Axel Rochaud and Stellia Sebihi

      Published by Charlotte Recapet the April 27, 2021 on 9:06 AM

      Today's ecotoxicology

      For a long time, ecotoxicology focused on the lethal effects of pollutants, with increased individual mortality translating into smaller population size or population extinction. There has been a shift from the study of lethal doses to the impact of smaller doses on more specific processes such as physiology and behaviour (Rand and Petrocelli, 1985; Døving, 1991). The article deals with the effect of pollutants on moulting.

      Possible use of ecotoxicology (the case of the article)

      Pollutants are an environmental factor causing stress in individuals. Lack of resources is another factor. For this reason, the study attempts to demonstrate and quantify the impact of food quality on the resistance to pollutants of moulting organisms.

      Hypotheses of the effect of the diet on the assimilation and detoxification of pollutants

      When a pollutant is assimilated by an organism, the body sets up the detoxification system, but it requires energy. Food allows the assimilation of energy by organisms. Good quality of food makes an individual capable of accumulating the energy necessary to ensure vital functions. An organism with energy from good quality food, should be able to activate an effective detoxification. Thanks to this detoxification, the body should be less impacted by pollutants. The study seeks to demonstrate whether this is true.


      Hypotheses illustration

      The interest of the biological model

      Gammaridae are macro-invertebrates that are mainly detritus feeders. They feed on detritus, corpses, living or decaying plants. Moreover, they are at the base of the human food chain as they are often industrially bred as fish food. Gammaridae are used to determine the biological quality of watercourses. They are rather pollution tolerant organisms but are nevertheless affected by pollution. Could the physiological changes noticed in Gammaridae be noticed in humans?


      A picture of two Gammaridae

      Way to understand the effects

      The experiment is designed to evaluate single and combined effects of leaf litter stoichiometric quality and Cd exposure on G. fossarum survival and growth. Phosphorus (P) is used as the nutrient in leaf litter. Cadmium (Cd) is used as the pollutant. Phosphorus (P) is a nutrient naturally present in the Gammaridae's food, in this case, leaf litter. Also, industrial activities are often sources of cadmium released into aquatic environments. The main route of exposure to cadmium (Cd) is through the ingestion of contaminated water and food, so Gammaridae is particularly exposed to this type of pollutant.


      The experiment design

      144 microcosms were performed for each of the 3 levels of Cd concentrations (0 ; 0.35 ; 0.7). For each group, 72 microcosms were realised with Sycamore discs and 72 with Alder discs. It allows to observe the effect in different conditions. Then, among these 72 microcosms, three batches of 24 have been realized. The first batch is a control batch where the composition of the litter was not modified. The second batch was a P- batch, where the litter was deficient in phosphorus and therefore in nutritional value (and which does not allow individuals to extract a lot of energy). Finally, the third lot was P+, it was enriched in phosphorus, the nutritional value is very good.

      Several metrics were measured to validate the initial hypotheses. The metrics were chosen for their relevance to evaluate organisms sensitivity to resources quality (leaf species and P content) and pollutant (Cd concentration in water): Cd bioaccumulation and survival rate. But also for their ecological importance: time-to-death, mass growth, time to moult and feeding rate.

      Results to remember

      • The Gammaridae's moult frequency and growth is amplified by a nutrient-rich diet (P+).
      • A presence of pollutants (cadmium) in the Gammaridae’s life site reduces their growth and raise their probability of death.
      • A nutrient-rich diet amplified effects of cadmium.
      • If we make the connection: The higher quality of food ressources, the more moulting there is and the greater the effect of cadmium. So moulting makes Gammaridae vulnerable to pollutants.
      • Species sensitivity to pollutants might be underestimated in ecosystems facing both nutrient constraint and pollutant.


      Schematization of the main results

      What to infer from this experiment.

      The presence of pollutants in the water causes problems in the survival of Gammaridae. Ecotoxicologists are well aware of the bioaccumulation of pollutants in the food chain. As a result, a predator will be more contaminated by the pollutants than is prey. Indeed, predators will keep in them the majority of the pollutants present in their prey. Thus, humans present in the upper part of the trophic chain will be much more contaminated than the Gammare.

      So why discharge pollutants into the water? Let's drink it directly!

      Read the full study: Arce-Funck, J., Crenier, C., Danger, M., Billoir, E., Usseglio-Polatera, P., and Felten, V. (2018) High stoichiometric food quality increases moulting organism vulnerability to pollutant impacts: An experimental test with Gammarus fossarum (Crustacea: Amphipoda), Science of The Total Environment, 645, 1484-1495, https://doi.org/10.1016/j.scitotenv.2018.07.227.

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    • Pyramids, built by the Egyptians and reversed by sharksby Pierre Labourgade, Valentin Santanbien and Morgan Schler

      Published by Charlotte Recapet the October 5, 2020 on 8:28 AM

      The case of a extreme inverted trophic pyramid of reef sharks supported by spawning groupers in Fakarava, French Polynesia

      Predators play a key role in the structure and functioning of ecosystems (Paine 1966; Begon et al. 2006). Through food webs, the relationship between preys and predators is crucial in order to maintain a balance, including in marine ecosystems (Woodson et al. 2018). A trophic pyramid is a graphic representation designed to show the biomass at each level of the food chain. The lowest level starts with decomposers and the pyramid ends with top predators. This is called a pyramid because generally, the biomass in the lower levels turns out to be much higher than in the upper levels (Figure 1 A). However, in the marine environment, and in some remote and almost unoccupied areas, predators may dominate in terms of biomass, generating an inverted pyramid (Figure 1 B).


      Figure 1 Diagram of a normal (A) and inverted (B) trophic pyramid

      Aggregations of grey reef sharks, Carcharhinus amblyrhynchos are observed on some reefs in the Indo-Pacific (Robbins 2006) (Figure 2). The southern pass of Fakarava atoll in French Polynesia has a population of around 600 individuals of this species (Mourier et al. 2016) (Figure 3). This makes it one of the few places to present such a large grouping. With such a large population on a reef channel of just over 1 kilometer, the area has up to three times the biomass per hectare documented for any other reef shark aggregation (Nadon et al. 2012). The biomass of predators is then much greater than preys, thus generating an inverted trophic pyramid. During this study, scientists tried to understand how those large group of sharks can survive when prey biomass is insufficient.


      Figure 2. Aggregation of grey reef sharks


      Figure 3. Panoramic view of Fakarava atoll

      During the study period, video-assisted underwater visual surveys conducted across the pass allow the researchers to find that sharks population can represent up to 700 individuals. Then, scientists use bioenergetic models based on known value of parameters that influence energetics needs of shark-like “asymptotic length”, “growth rate” or “proportion of fish in the diet” to determine prey biomass needed for all the individuals. According to bioenergetic models, the food requirements to maintain that large population is approximately 90 tons of fish per year, which is not provided by the environment as it is. However, the pass is used as a breeding ground for many fish species, thereby reducing the prey-shark ratio. This means that the prey biomass will be much higher than that of sharks during these reproduction periods (Mourier et al. 2016), leading to frenetic predation behavior in the shark that will allow it to meet its energy needs (Robbins and Renaud 2016; Weideli, Mourier, and Planes 2015). Furthermore, the continuous presence of prey aggregation is ensured by the successive migration of different species to this site, in order to meet the metabolic demands of the shark population present (Craig 1998). With simulation-based on researcher bioenergetic model, sharks would not have enough energetic income after 75 days if other prey species didn’t migrate to the pass. There is, therefore, an idea of metapopulation where the exchange of individuals between populations in normal and inverted trophic pyramids ensures that the energy needs of each individual are met (Figure 4). This exchange of individuals between populations will allow the long-term maintenance of the species and, in the case presented here, of the shark.


      Figure 3. Diagram of the transfer of potential prey for the shark between two normal pyramids and one inverted trophic pyramid via migratory flows

      The temporal aspect in the movement of individuals between populations is therefore important to be considered during the development of management and conservation measures. Indeed, if we want to ensure the sustainability of the grey reef shark in this pass, we must not only protect the habitat on-site, but also the original habitat of different species that come to reproduce in the pass. These species are indeed essential for the survival of sharks since they represent the only source of energy available during certain periods of the year.

      Read the full study: Mourier, J., Maynard, J., Parravicini, V., Ballesta, L., Clua, E., Domeier, M.L., and Planes, S. (2016). Extreme inverted trophic pyramid of reef sharks supported by spawning groupers. Current Biology 26 (15): 2011–2016.

      Other cited articles:

      Begon, Michael, Colin R. Townsend, et John L. Harper. 2006. Ecology: from individuals to ecosystems. Sirsi i9781405111171.

      Craig, P. C. (1998). Temporal spawning patterns of several surgeonfishes and wrasses in American Samoa. Pacific Science, 52(1), 35-39.

      Nadon, M. O., Baum, J.K., Williams, I.D., McPherson, J.M., Zgliczynski, B.J., Richards, B.L., Schroeder, R.E., and Brainard, R.E. (2012). Re-creating missing population baselines for Pacific reef sharks. Conservation Biology 26 (3): 493–503.

      Paine, R.T. (1966). Food web complexity and species diversity. The American Naturalist 100 (910): 65–75.

      Robbins, W. D., and Renaud, P. (2016). Foraging mode of the grey reef shark, Carcharhinus amblyrhynchos, under two different scenarios. Coral Reefs 35 (1): 253–260.

      Robbins, W.D. (2006). Abundance, demography and population structure of the grey reef shark (Carcharhinus amblyrhynchos) and the white tip reef shark (Triaenodon obesus)(Fam. Charcharhinidae). PhD Thesis, James Cook University.

      Weideli, O. C., Mourier, J., and Planes, S. (2015). A massive surgeonfish aggregation creates a unique opportunity for reef sharks. Coral Reefs 34 (3): 835–835.

      Woodson, C. B., Schramski, J.R., and Joye, S.B. (2018). A unifying theory for top-heavy ecosystem structure in the ocean. Nature communications 9 (1): 1–8.

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    • A new way to understand the effects of toxic compoundsby Flore Emonnot and Anne Michaud

      Published by Charlotte Recapet the September 7, 2020 on 8:07 AM

      Water pollution is a major concern. It can be induced by many elements. For example, Cadmium (Cd) which belongs to the heavy metals family can be source of pollution in certain concentrations. This element is naturally present in the environment, but the use of agricultural chemicals has been indicated as the main anthropogenic source of Cd pollution in aquatic environments. The organisms living in these aquatic ecosystems are exposed to this pollution. Moreover, this compound is bioaccumulated in organs and tissues, so it can induce damages. 


      Daphnia magna

      That is why it is important to evaluate the effects of this pollutant on organisms. Daphnia magna (a cladoceran crustacean) is one of the most widely used animals in aquatic toxicology. In terms of sensitivity to toxic substances, it is generally thought to be representative of other zooplankters (Anderson, 1944).  It plays an important role in the balance of an ecosystem, because of its position on the first levels of the food chain. Also, D. magna enhances water purification by filtering water and retaining food particles, it is its way to eat. This animal spends its whole life in a variety of freshwater environments.  As long as the conditions remain favourable, it reproduces predominantly by parthenogenesis.

      Bioassays are used in aquatic toxicology to provide individual-level information, while ecotoxicology is assessing the impact of pollution on populations. The DEB theory (Dynamic Energy Budget) is a theory that describes the aspects of metabolism (energy and mass budgets) at the individual level. Food assimilation results in energy, which can then be used for reproduction, growth or maintenance (life-history traits). The DEBtox is a toxicological application of the DEB theory which attempts to assess the effects of pollutants on life-history traits over time.

      The key challenge is how to infer the impact of toxic effects observed in individuals and apply it to an entire population. Elise Billoir and her team combined the following tools to extrapolate the individual effects to the entire population:

      The DEBtox is a good way of modeling survival, reproduction and growth continuously as a function of time and exposure concentration and at the individual level.

      The population growth rate (which incorporates lethal and sublethal effects), is the best parameter to evaluate the risk of a pollutant on a population, hence matrix population models are a useful tool. Billoir explains that in population matrix, population is divided into classes based on development stage, and individuals transfer from a class to the next one depending on their survival and their fecundity.

      By combining DEBtox theory and matrix population models, it is possible to extrapolate every effect of the toxic compound on the individual to the population level (as explained in the synthetic diagram below). 

      This technique used by Billoir, has not yet been used in an ecotoxicological context. It consists of reorganizing all the age-specific information in a stage-specific way. This way it makes possible to compare the sensitivity in the face of cadmium and in relation to the age of the individual. 


      Diagram of the method developed in the study of Billoir et al.

      In this case, the sensitivity analyses showed that the effects of cadmium at the individual level were not significant but the application of the model proved that the population growth rate is highly affected through the cadmium contamination. Moreover, we think that this model could be applied to similar aquatic organisms and other pollutants such as heavy metals and could be useful to enhance existing bio-indicators of water quality.

      Read the full study: Billoir, E., Péry, A.R.R. , and Charles, S. (2007) Integrating the lethal and sublethal effects of toxic compounds into the population dynamics of Daphnia magna: A combination of the DEBtox and matrix population models. Ecological Modelling, 203(3–4), 204-214. https://doi.org/10.1016/j.ecolmodel.2006.11.021.

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    • Spatial response of plaice and sole to climate changeby Arnaud Dupond and Alix Pascal

      Published by Charlotte Recapet the August 3, 2020 on 7:54 AM

      Scientists admit that climate change is one of the main driving forces which change species distribution and abundance in many ecosystems.

      In this case, a modification of abiotic variables can affect the “niche concept” and can also change species geographical distributions. For the marine environment, this notion of geographical dependence is important. Indeed, marine organisms show several distinct stages during their life and each of these stages evolve in a specific habitat.

      The objective of this study was to use different models based on physiological aspects and environmental variables in order to estimate habitat occupation by plaice and sole under different climate change scenarios in the North Sea.

      How to reach this objective?

      To predict new habitats, researchers considered environmental variables and determined their effect on the food web, but also the effect of the food web on the water chemistry.  To do that, the ecosystem model used functional groups of taxa. Their taxa are phytoplanktonic, planktonic and macrobenthic organisms. Some of them have a direct effect on the water chemistry and are regulated by other taxa. The food web is also used to quantify the availability of the habitat’s resources. Thanks, of this two types of model results fit more precisely reality of the distribution.

      The sample strategy is built like this, data are collected daily on surface of 10x10km sin the North Sea.


      Figure 1: Schematic simplification of the models used in the studies

      Results of the study

      The model of environmental variables shows the predictions for temperature and food conditions between 1989 and 2002. This data showed benthic production is concentrated along the southern coast during the year 1989, whereas in 2002 is concentrated in the Southern bight (figure 2).


      Figure 2: Comparison of the benthic production between 1989 and 2002 in the North Sea

      An important fact is that the temperature rate inside of which the growth is positive will change with the size of the fish and according to abundance of food (the more food is abundant the higher rate of temperature is). Indeed, bigger fish need higher temperature to grow optimally. Figure 3 defines the areas of maximum potential daily growth of each class size of plaices in 1989 at the left, and in 2002 at the right.


      Figure 3: Comparison between the three size ranges of plaices and soles, of the speed growth in regard of two environmental parameters, the food availability and the temperature

      The results for maximum potential growth per day seem to give the same result as the estimate of average abundance. (Figure 4).


      Figure 4: Comparison of the plaice and sole abundance distribution in the North Sea

      Conclusion

      For the plaice, migrations during different stages of life maximize their physiological performance during the summer season, in the winter, the adult’s distribution is determined by the best spawning habitat and shows maximisation of their fitness. Sole differs in their physiological traits and have a higher optimal growth temperature which explains the difference in life habitat. As for plaice, the area indicated high quality habitat for the different size class.

      This study can predict the evolution of species distribution with a model of environmental changes and one of physiological changes but in our case,  we can just explain data collected not the prediction made with the model.

      Read the full study: Teal, L.R., van Hal, R., van Kooten, T., Ruardij, P. and Rijnsdorp, A.D. (2012), Bio‐energetics underpins the spatial response of North Sea plaice (Pleuronectes platessa L.) and sole (Solea solea L.) to climate change. Glob Change Biol, 18, 3291-3305. https://doi.org/10.1111/j.1365-2486.2012.02795.x

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    • Microplastics: no effect on the productivity of the marine environment?!by Amaelle Bisch and Anaelle Bouloy

      Published by Charlotte Recapet the July 6, 2020 on 2:45 PM

      According to the paper: “Do microplastics affect marine ecosystem productivity?” by Troost et al. 2018, microplastics would have almost no effect on primary and secondary production, or at least this effect could not be demonstrated! 

      But what are microplastics?

      Plastics appeared at the beginning of the 20th century and quickly became indispensable in everyday life. Plastics are composed of polymers (long carbon chain) of synthetic or natural origin. Microplastics are plastic particles smaller than 5 mm (. There are two types of microplastics: primary (directly manufactured at this size) and secondary (resulting from the degradation of macroplastics). The major disadvantage of microplastics is that they are easily ingested by marine biota (2,3).

       

       

       

      Primary production, the basic link in a long chain 

      Primary producers are at the base of the trophic chain. They are autotrophic organisms that produce their organic matter from a light (photosynthesis) or mineral source. In the marine environment, these organisms correspond to algae, phytoplankton and cyanobacteria and are the basis for zooplankton feeding. Zooplankton are secondary producers and heterotrophic organisms unable to synthesize their organic matter.


      Phytoplankton

      Zooplankton

      How can microplastics affect these organisms?

      In most of laboratory experiments, the impacts showed on plankton, they were for primary producers an inhibition on the algae growth, chlorophyll content and photosynthesis (4,5,6). For zooplankton, it was observed a reduced food consumption and an increasing in energy consumption with a low allocation of this energy for growth (7,8). But these effects depend to the species of plankton and the nature of microplastics (9). However, are these observations noted in the laboratory really transposable to the ecosystem scale?

      The models spoke...

      The study by Troost et al. (1) shows, by means of modelling, that at the level of primary production (algal biomass) there is no significant impact of microplastics. Indeed, this can be explained by different theories: (i) environmental conditions (availability of nutrients and light) already strongly impact the growth of algae, (ii) a transport technique (advection) would provide some protection.

      Concerning zooplankton, or secondary production, the impact of microplastics is considered low over the entire North Sea because the observed changes are both positive and negative and therefore compensate each other. Exposure to microplastics leads to changes in spatial patterns and strangely enough the impact is not greatest in areas with the highest concentration of microplastics. Surprising but not so much because this can be explained simply by the small concentrations of algae found in off-shore areas (areas with the least concentration of microplastics) making zooplankton more sensitive to any change.

      And how they have managed to demonstrate that?

      The difficulty lies in a successfully integration of the data observed in the laboratory into an ecosystem-scale model. They modelled biogeochemical transport, hydrodynamics, nutrient inputs from rivers, primary production, zooplankton biomass and also microplastic concentrations in the North Sea. In the end, the results obtained are only based on modelling and could not be verified in the field, so the conclusions should be "swallowed" with caution.

      Cited articles

      1. Troost, A., Desclaux T., Leslie, A., Van Der Meulen, M., Dick Vethaak, A., 2018. Do microplastics affect marine ecosystem productivity? Marine Pollution Bulletin 135 (2018) 17–29
      2. Ivar do Sul, J., Costa, M.F., 2014. The present and future of microplastic pollution in the marine environment. Environ. Pollut. 185, 352–364. http://dx.doi.org/10.1016/j. envpol.2013.10.036.
      3. GESAMP, 2016. Sources, fate and effects of microplastics in the marine environment: part two of a global assessment. In: Kershaw, P.J., Rochmann, C.M. (Eds.), IMO/FAO/ UNESCO-IOC/UNIDO/WMO/IAEA/UN/ UNEP/UNDP Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection. Rep. Stud. 2016pp. 220 GESAMP No. 93.
      4. Zhang, C., et al., 2017. Toxic effects of microplastic on marine microalgae Skeletonema costatum: interactions between microplastic and algae. Environ. Pollut. 220, 1282–1288.
      5. Sjollema, S.B., et al., 2016. Do plastic particles affect microalgal photosynthesis and growth? Aquat. Toxicol. 170, 259–261.
      6. Casado, M.P., et al., 2013. Ecotoxicological assessment of silica and polystyrene nano-particles assessed by a multitrophic test battery. Environ. Int. 51, 97–105.
      7. Watts, A.J., et al., 2015. Ingestion of plastic microfibers by the crab carcinus maenas and its effect on food consumption and energy balance. Environ. Sci. Technol. 49, 14597–14604.
      8. Van Cauwenberghe, L., et al., 2015. Microplastics are taken up by mussels (Mytilus edulis) and lugworms (Arenicola marina) living in natural habitats. Environ. Pollut. 199, 10–17.
      9. Wenfeng Wang, Hui Gao, Shuaichen Jin, Ruijing Li, Guangshui Na, 2019. The ecotoxicological effects of microplastics on aquatic food web, from primary producer to human: A review. Ecotoxicology and Environmental Safety 173, 110–117

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    • A little bit of salt and heat... a good recipe for goby metabolism?by Maxime Deau, Quentin Garreau and Dorian Raoux

      Published by Charlotte Recapet the June 1, 2020 on 2:18 PM

      As the literature shows, a variety of factors influence the well-being of fish populations. For example, we know that some fish may or may not be very sensitive to changes in the conditions of their living environment (water temperature or salinity). These changes can affect their metabolism (reduced fertility, growth, etc.) or even, in the worst case, lead to the death of individuals. The goby (Pomatoschistusmicrops) (Figure 1), a relatively tolerant species and an essential central link in the food web is one of the species studied in the observation of the impact of these changes on the fish fauna in the Minho estuary in Portugal (Figure 2).

      In this study, the researchers were able to model the evolutionary dynamics of p.microps populations based on models that take into account different parameters of goby's life cycle like fertility, mortality, migration rate and the effect of  environmental parameters such as salinity and temperature. The aim of these models is to describe the evolution of the  different life stages of this fish by establishing the possible impacts of climate change on their metabolism. In this framework, they studied both the impacts of temperature and salinity and combined the impact of both.

      It has been noted that salinity directly influences the metabolism of individuals. Indeed, it plays a particular role in the survival of many aquatic organisms but also on their growth (strong allocation of energy to osmoregulation; Rigal, F. and al.,2008). Therefore, it plays a role in the growth of the goby as well as indirectly on its prey. The latter will be less available, which implies a higher energy expenditure for predation. However, this species resists large variations in salinity (0 to 51 psu). For temperatures, the impact is more diverse. Since the goby does not thermoregulate, its metabolism is directly influenced by the temperature of the environment. In addition to its significant effect on pregnancy, it also has an impact on migration, reproduction, recruitment and mortality. (Sogard, 1997; Hurst et al., 2000; Hales and Able,2001; Hurst, 2007; Jones and Miller, 1966; Claridge et al.,1985; Wiederholm, 1987).

      Regarding the goby’s responses to these parameters, the research team has implemented them in the model, running different scenarios (salinity and temperature variations). Temperature and salinity variations studied separately led to population crash, except for a salinity lower than the current state ( -5psu). However, the combination of the two variables gave scenarios showing an increase in the population when the salinity was -5 psu, with temperatures ranging from +1 to +3°C, with an optimum at +2°C (see figure 5).
      For example, in extreme temperatures, the fish activity will be greatly reduced, which will imply a decrease in the search for preys or sexual partners, causing feeding and mating problems (predation of eggs by males (Magnhagen, 1992). However, a slight increase in temperature could cause a longer reproduction period, allowing for a greater number of offspring to be generated. It has also been noted that with an increase in temperature, there is a delay in the breeding period, leading to the appearance of offspring in a period that may be less favorable for their proper development (early winter/lower metabolism).

      In conclusion, climate change, through its effects on water temperature and salinity, will have a significant impact  on common goby populations. Indeed, these parameters have a great influence on the metabolism of these fish (whatever  their stage of development).In many scenarios, increases in temperature and salinity can cause crash populations. But  beware, in some cases (increase in temperature and decrease in salinity) the population of Pomatoschistus microps would tend to increase. Even if this scenario seems favorable for this species, some others will suffer. in fact, a study conducted on Arctic fish species has confirmed these trends

      It is therefore clear that climate change affects population dynamics by changing fish environment and impacting their metabolism. It’s therefore important to continue this kind of study to have a better idea of these repercussion on a global scale. We are largely responsible for climate change, so it is up to us to make sure that we limit our impacts. Here is a link that will teach you how to reduce your carbon footprint through 20 examples of simple everyday actions: http://www.globalstewards.org/reduce-carbon-footprint.htm

      Read the full study: Souza, A.T., Ilarri, M.I., Timóteo, S., Marques, J.C., Martins, I. (2018) Assessing the effects of temperature and salinity oscillations on a key mesopredator fish from European coastal systems, Science of The Total Environment 640–641, 1332-1345, https://doi.org/10.1016/j.scitotenv.2018.05.348.

      Other cited studies:

      Claridge, P.N., Hardisty,M.W., Potter, I.C., Williams, C.V., 1985. Abundance, life history and ligulosis in the Gobies (Teleostei) of the inner Severn Estuary. J.Mar. Biol. Assoc. U. K. 65, 951–968.
      Hales, L.S., Able, K.W., 2001.Winter mortality, growth, and behavior of young-of-the-year of four coastal fishes in New Jersey (USA) waters. Mar. Biol. 139, 45–54.
      Hurst, T., 2007. Causes and consequences of winter mortality in fishes. J. Fish Biol. 71, 315–345.
      Hurst, T.P., Schultz, E.T., Conover, D.O., 2000. Seasonal energy dynamics of young of the year Hudson River striped bass. Trans. Am. Fish. Soc. Taylor & Francis 129, 145–157.
      Jones, D., Miller, P.J., 1966. Seasonal migrations of the common Goby, Pomatoschistus microps (Kroyer), in Morecambe Bay and elsewhere. Hydrobiologia 27, 515–528.
      Magnhagen, C., 1992. Alternative reproductive behaviour in the common goby, Pomatoschistus microps: an ontogenetic gradient? Anim. Behav. 44, 182–184.
      Rigal, F., Chevalier, T., Lorin-Nebel, C., Charmantier, G., Tomasini, J.-A., Aujoulat, F., Berrebi, P., 2008. Osmoregulation as a potential factor for the differential distribution of two cryptic gobiid species, Pomatoschistus microps and P. marmoratus in French Mediterranean lagoons. Sci. Mar. 72, 469–476.
      Sogard, S.M., 1997. Size-selective mortality in the juvenile stage of teleost fishes: a review. Bull. Mar. Sci. 60, 1129–1157.
      Wiederholm, A.-M., 1987. Distribution of Pomatoschistus minutus and P. microps (Gobiidae, Pisces) in the Bothnian Sea: importance of salinity and temperature.Memoranda Societatis pro fauna et flora Fennica 63, 56–62.

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    • Shad, those endangered travelersby Alicia Dragotta and Claire Valleteau

      Published by Charlotte Recapet the April 6, 2020 on 1:52 PM


      Photograph by MRM association

      Shad are migratory fish that travel great distances between sea and river in order to reproduce. These long journeys are the source of great energy expenditure, particularly to find the most favourable spawn environment. These species are considered bio-indicators of our waterways. Their presence or absence indicates the ecological state of the water. Migratory distance was governed by energetics, behaviors, maturation, and upstream delays at dams. Individual adult migrant American shad (Alosa sapidissima) ascend the Connecticut River and spawn, and survivors return to the marine environment. Theodore Castro-Santos and Benjamin H. Letcher presented a simulation model of these behaviors.

      The purpose of this model is to evaluate the effects of biological and physical variables on adult spawning success and survival. Only energy devoted to migration has been taken into account in the model. Physiology and energetics strongly affected distribution of spawning efforts and survival into the marine environment. Delays to both upstream and downstream movements had dramatic effects on spawning success. Other factors influencing migratory distance included entry date, body length, and initial energy content. Furthermore, dams alter reproductive success and have an impact on migration (delay).

      This model suggests shad that spend more time in the river have greater spawning success but are more likely to die of energy depletion.  Many important factors in the models presented here remain enigmatic. Perhaps the most important question is what causes shad to reverse direction and migrate downstream. Do both energetics and maturation play a role ?

      Answering this question could be difficult but may be possible using, say, a combination of physiological telemetry (e.g., Hinch et al. 1996) and data on reproductive status, especially of downstream migrants.  The purpose of this paper was to develop a management tool to evaluate the relative importance of biological and physical factors on shad reproduction and survival. Restoring access to spawning habitat by providing fish passage has been a central management strategy. Ecological continuum is very important to preserve species, including these migratory fish. Dams for example, were built for many reasons, at the origins in order to mill operations, and today for hydraulic energy exploitation. We have to reconsider the interest of these dams, remove those which are useless and adapt the others. This process has been under way for several years, opening the door to restoring access to the rivers.

      Read the full study: Castro-Santos, T. and Letcher, B.H. (2010) Modeling migratory energetics of Connecticut River American shad (Alosa sapidissima): implications for the conservation of an iteroparous anadromous fish. Canadian Journal of Fisheries and Aquatic Sciences. 67(5): 806-830. https://doi.org/10.1139/F10-026

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    • Corals and algae, a relationship in danger: a model to predict their future! by Clara Dignan, Anna Gago and Anabelle Leblond

      Published by Charlotte Recapet the March 2, 2020 on 2:14 PM


      Bleached branching coral (foreground) and normal branching coral (background). Keppel Islands, Great Barrier Reef

      Corals that come together to form coral reefs are shelter to 25% of our planet's marine life according to the WWF. This biodiversity is fundamental. It’s both a source of income and food, and it provides irreplaceable services to humanity. But today coral reefs are in danger. They are directly threatened by global warming. In forty years, 40% of the reefs have already disappeared and scientists agree that if nothing is done by 2050, all of them will be gone (Coral guardian).

      Coral polyps and algae, an endosymbiotic relationship

      Coral bleaching has now become a major global concern for the future of coral reefs. Temperature rise appears to be one of the main causes of bleaching, affecting growth, feeding and other ecological processes on reefs. This bleaching phenomenon is due to the expulsion of zooxanthellae, the symbiotic microalgae living in the tissues of the polyps (the coral is made up of a colony of polyps that participate in the making of its skeleton). These unicellular algae carry out photosynthesis and provide, for the most part, the energy that corals need to develop and grow. Exchanges between the polyp and the zooxanthellae mainly concern nitrogen, phosphorus, carbon and biosynthetic intermediates. The presence of zooxanthellae being responsible for the color of the colonies, bleaching is therefore the symptom of a coral which is no longer in symbiosis, which generally results in the death of the coral.


      The coral-symbiont relationship and its interaction with the overlying water column.

      Prediction models

      Since few year, scientists analyze corals and try to predict their bleaching evolution. In this aim, a collaboration between several organizations such as CSIRO have set up a first hydrodynamic, sedimentary and biogeochemical model called: « eReef ». This model simulates the environmental conditions as the temperature, the background light and the organic nutrient concentration of the Great Barrier Reef at several scales. It allows accurate prediction of factors influencing coral processes from satellite remote sensing images.

      However, for more representative modelling, it is necessary to apply models that take into account the coral-symbiont relationship and the stress related to environmental variations. In this framework, Baird et al. have developed a model which, in parallel to the environmental conditions obtained from the « eReef » model, also takes into account essential parameters in the symbiotic process such as biomass and growth rate of zooxanthellae, pigment concentration, nutritional status as well as tolerance characteristics such as sensitivity to reactive oxygen concentration (oxidative stress).


      The eReefs coupled hydrodynamic, sediment, optical, biogeochemical model. Orange labels represent components that either scatter or absorb light levels. (For a better understanding of the colour used and the abbreviations, the reader is referred to the web version of the article)

      Take home message

      This coral bleaching model applied under realistic environmental conditions has the potential to generate more detailed predictions than satellite coral bleaching measurements. In addition to predicting coral bleaching, this model will now make it possible to evaluate management strategies, such as the introduction of temperature-tolerant individuals or species or localized shading.

      Nevertheless, this model is still too simplistic to make real predictions. It is based only on the process of a single type of coral and macro-algae and does not take into account all phenomena related to bleaching. It is therefore seen as a step forward for science that could allow for future reevaluations of the effects of bleaching.

      Bibliography

      Cited study: Bairda, M.E., Mongina, M., Rizwia, F., Bayb, L.K., Cantinb, N.E., Soja-Woźniaka, M., Skerratta, J. (2018). A mechanistic model of coral bleaching due to temperature-mediated light-driven reactive oxygen build-up in zooxanthellae. Ecological Modelling 386, 20-37. https://doi.org/10.1016/j.ecolmodel.2018.07.013

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    • Why should we think about cougars when planning our cities?by Amaïa Lamarins and Gautier Magné

      Published by Charlotte Recapet the February 3, 2020 on 2:02 PM


      A puma family above the nighttime lights of San Jose - National Geographic - (photo courtesy of Chris Fust)

      Humans have modified 75% of earth land surface which has important consequences on wildlife. In fact, human presence and activities are perceived as a threat by animals which adapt their behaviors to avoid it. Gaynor and his collaborators’ meta-analysis showed that many species are modifying their daily activities and identified 117 diurnal mammals becoming more and more active at night. Consequently, these animals face constrained access to resources and are susceptible to shifting their diet to nocturnal prey. Thus, anthropic activities influence growth, breeding, survival and community interactions of wild animals.

       
      Shift in rhythmic activity of diurnal species due to human disturbance - Ana Benítez-López.

      In southern California, the habitat of cougars, an apex nocturnal predator, is reduced by the expansion of cities. No, we’re not talking about the rampant nightclub predators (whose habitats remain undisturbed), we’re talking about mountain lions! You’ve probably already heard about pumas roaming across big cities like Santa Cruz, California. They likely are not curious tourists hoping to take in the sites, but are rather disturbed by human activities, which cause their nighttime activity to be higher in developed areas than in natural ones. This shift increases their daily energy expenditure: because of humans, pumas need to eat around 160-190 kg of additional meat per year (for females and males, respectively)! Are there sufficient deer populations to meet these needs? Unfortunately, it seems not, since a significant number of puma attacks on cattle have been recorded.

      These results, showing human-induced behavioral change for pumas, come from a recent study published by members of the Santa Cruz puma project. By wide-scale monitoring of 22 wild pumas, they were able to link their behavior with their subsequent energetic expenditures: pumas’ behavior and movement were measured through spatial GPS location data, recorded every 15min, and energetic cost of movement was estimated considering their weight and travel velocity. An interesting methodological point to note: in order to avoid underestimating the energy expenditures via GPS tracking, scientists calibrated their estimations using accelerometers. Thanks to these methods they figured out the effect of housing densities on pumas’ activity and energetic costs, taking into consideration the time of day and sex of the animal.

      Indeed, they were right in taking into account these factors because, according to their findings, response to human activities differs between day and night and between males and females. During the day pumas are more likely to stay inactive, especially near urban areas. At night, being close to houses increases time spent active by 8.8% and 5.8%, respectively, for males and females. Consequently, estimated daily caloric expenditure increases by 11.6% for males and 10.1% for females in high housing density areas. Below you will find an outline summarizing these results:


      Urban development negatively affects pumas by increasing nighttime activity and energy expenditure.

      Such studies underline the role of bioenergetics to estimate the costs of human-induced behavioral changes but do not provide insight on global energetic allocation. Further work is needed to understand the consequences of energetic balance disturbances and identify which individual functions are affected (growth, maintenance, maturation or reproduction). Besides, human impact could be underestimated because such tracking doesn’t allow us to know if pumas get all available energy from their prey near humans; some observations reported they often have to leave their prey because they fear humans. This partial feeding would constrain pumas to hunt more prey!

      Unfortunately, this is not the only human-induced threat affecting pumas. In the region of Santa Cruz and southern California, they are targeted by ranchers, resulting in political tension about their conservation. In fact, cougars have been protected since 1990. However, 98 pumas are killed each year due to depredation hunting permits. It appears necessary to ensure coexistence between urban development, human activities, puma populations and their prey. In a recent study, development strategies are suggested, such as rural residence development, to ensure landscape connectivity and conservation of parcels where pumas have been geo-located. Nowadays, no cities are expanding regarding puma, deer or other wild animals’ living areas (to our modest knowledge!). The only measures taken when pumas are too close to urban zones consist in doing nothing or frightening or relocating it, and in the worst case killing it. And if designing our lives and activities regarding nature and wildlife was the challenge of tomorrow, would you be ready?


      Ideal residential development maintaining pumas landscape connectivity. Graphical abstract of the paper of Smith and al 2019

      Cited study: Wang, Y., Smith, J.A., Wilmers, C.C. (2017) Residential development alters behavior, movement, and energetics in an apex predator, the puma. PLoS ONE 12(10): e0184687. https://doi.org/10.1371/journal.pone.0184687

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    • Are pesticides more dangerous when you are hungry?by Angèle Lorient

      Published by Charlotte Recapet the January 6, 2020 on 1:52 PM

      Today, the impact of pesticides on our environment is a central issue in many publications and a major concern for all citizens. Between 2014 and 2016 the use of pesticides increased by 12%. Indeed, intensive farming currently used implies that we find in our food, in the air but also in water, traces of pesticides. A 2013 Inserm report highlights a link between exposure to pesticides and the appearance of cancer or pathology such as Parkinson's disease but also developmental problems on children. Therefore, they harm the health of humans but also the entire terrestrial and aquatic ecosystems.


      Water Flea Daphnia Magna. www.aquaportail.com

      In addition to using a large amount of chemicals, modern farming methods make soils less permeable. As a result, precipitation runoff is a major contributor to pesticide pollution from our streams. In order to study the toxicity of pesticides in the aquatic environment, the majority of laboratories use Daphnia as an indicator of water quality, and in particular the species Daphnia magna for their sensitivity to toxins.

      Daphnies are small crustaceans measuring about 1 to 4 millimeters. They live mainly in fresh water (river, pond, lakes). They are filter feeders that help maintain the clarity of the water thanks to their ability to eat green algae. During a day they move between the bottom and the surface of the water depending on the light (photoperiod).

      In 2006 a study was conducted by 4 scientists (2) to study the physiological responses (sensitivity, growth, reproduction) of daphnies to different dietary concentrations of the same pesticide to which they and their mothers were subjected. (high food or low food).

      The study shows that lack of food does not play a direct role in the sensitivity of daphnies to the pesticide in question. However, it is one of the factors determining the level of absorption and elimination of this toxic substance by the body. In addition, the energy used to fight this toxin has a negative effect on the maintenance of vital functions.

      In a period of low availability of food resources, invertebrates will have a more limited growth and a lower reproductive rate in proportion to the level of pesticide present in their environment. While the impact is less when they are subject to sufficient food resources (Fig 1).

      For the different types of food resource, the effect of the pesticide concentration is proportional to the survival rate. On the other hand, we can notice that there is a threshold effect concerning growth and reproduction.

      However, they also highlighted that these individuals, when no longer subject to the pesticide, found a normal activity (resilience).

      This study makes it possible to highlight the potential impacts on the results of the experiments if certain non-standardized conditions vary between laboratories (concentration of food, respect of the photoperiod). As well as the differences in test organism responses between conventional environmental conditions (controlled artificial environment) and the natural environment (subject to variations).

      The analysis of the results of this study raises the following questions:

      • What is happening in the longer term?
      • Does the repeated presence of pesticide pulses have the same physiological effects on an individual throughout his life?
      • Is the speed of resilience due to the species or can it vary individually?
      • Is there resiliency of newborns from underfed mothers?

      It also shows the urgency of taking into account the impacts of pesticides, both on our current health, on the heritage that we will transmit, but also on our ability to reproduce. Despite the mobilization of the Ministry of Agriculture including the program "Ambition bio 2017" there is urgency. Pesticides are one of the main causes of pollution in our waterways. This pollution endangers aquatic life, as has been demonstrated, but also the drinking water resource. Should not our entire consumption system be called into question in order to be able to realistically implement the planned management plans?

      Cited study: Pieters, B.J., Jager, T., Kraak, M.H.S., Admiraal, W. (2006) Modeling responses of Daphnia magna to pesticide pulse exposure under varying food conditions: intrinsic versus apparent sensitivity. Ecotoxicology 15, 601–608. https://doi.org/10.1007/s10646-006-0100-6

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    • What does the future has in store for red salmon in a context of global climate change?by Camille Sestac and Amandine Tauzin

      Published by Charlotte Recapet the November 1, 2019 on 1:18 PM

      Pacific salmon have extremely complex life histories and may be threatened by global climate change, as Peter S. Rand and colleagues investigate in their recent study.


      Life cycle of Sockeye Salmon

      Among all species, fishes must adapt to face disruptions caused by global climate change. Sockeye salmon (Oncorhyncus nerka), an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it, has a complex life cycle. As a migratory species, their energetic demands are high during spawning migration. Climate change might have important impacts on populations and their migration via variation of river discharge, increase of water temperature and decline of growth conditions. Aiming to better understand the impacts of these disruptions on the migratory performance of this species of salmon, Peter S. Rand from Wild Salmon Center teamed up with researchers from British Columbia. Their goal is to evaluate the effects of past and future trends in river discharge and temperature on the migratory performance of Sockeye Salmon in the Fraser River.

      In a context of global climate change, it is crucial to understand the effects of disruptions on ecosystems and the populations living in them. Indeed, it is important to know the impacts of these disruptions on every stage of their life cycle (the juvenile freshwater period, the estuarine period, and the subadult marine period) so that we can maintain the populations stock. It’s especially important for fishery management because the fishing quota has greatly increased over the last decades and has threatened populations of Pacific salmon, particularly during their spawning migration. That’s why with three main objectives, these scientists used analysis to improve the understanding of how changes in river conditions can affect the energy use and the mortality rate in Sockeye salmon population. To do so, they used several models: one to search a link between energetic conditions of individuals and en route mortality, one to simulate the energy use during spawning migration and one to hindcast and forecast energy use by simulating fish’s behaviour and migration conditions (for more information, a tip, read the article!).


      Long-range forecasts of lower Fraser river temperature during the summer of 2018

      Using these friendly models, Rand and his colleagues proved that energy reserves and energy depletion of early Stuart Sockeye salmon are major factors that can affect their ability to reach their spawning grounds. They also stated that energy depletion is a function of both river temperature and discharge. Therefore, this population is structured by condition-dependant mortality. Nevertheless, this group of researchers brought to light a mechanism that allows fishes to cope with some environmental variability, providing a certain degree of resilience over time. Therefore, even if energetic demands and migration mortality increase as a result of exposure to warmer temperatures, it will be compensated by reduced time travel to the spawning ground as the river flow will be lower.

      However, increase of temperature means increase of diseases appearing and developing and that stress added may be a direct cause of increased mortality during migration. Finally, as if it wasn’t already bad enough for our salmons, ocean productivity can be affected by climate change and thus affect their river migration success. In fact, this can lead to a decrease of body size and body energy content. It implies that individuals will start their migration with lower energy densities and will be more likely to exhaust their energy stock before even reaching the spawning grounds.


      Salmon jumping over a weir
      According to the US-Canada Commission, a 21° C temperature spike was measured on the Fraser River in 2009. However, sockeye salmon show signs of physiological stress and migratory difficulties above 19°C and from 20°C, the first signs of illness and death appear. But migration of Sockeye salmon is not only threatened by climate change. In fact, migration of salmon specially is impacted by humans or natural obstacles. Dams and weirs form large obstacles for this migratory species and can be very difficult to cross. Many studies have already proved that this kind of obstacles, even when equipped with crossing devices, delay their migration and thus jeopardize their reproduction. This can lead to a decline of the population and in some cases to its extinction, as it happened in Belgium.

      So, whilst some questions have been answered, it seems that more studies need to be carried out to improve our knowledge about the impact of global change which seems to be another sword of Damocles hanging over the head of Sockeye salmon.

      Cited paper: Rand, P.S. et al. (2011) Effects of River Discharge, Temperature, and Future Climates on Energetics and Mortality of Adult Migrating Fraser River Sockeye Salmon. Trans. Am. Fish. Soc. 135(3), 655-667. https://doi.org/10.1577/T05-023.1

      Featured images: Life cycle of Sockeye salmon by Camille Sestac, graph from https://www.pac.dfo-mpo.gc.ca/science/habitat/frw-rfo/index-eng.html , Sockeye Salmon from www.ryanvolberg.com

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    • Organisms and their environment: Dangerous liaisonsby Marius Dhamelincourt and Charlie Sarran

      Published by Charlotte Recapet the October 14, 2019 on 9:15 AM

      Preface

              Whatever the incredulous think, organisms are necessarily linked to their environment to survive, science says. However, this relation, unstable, can be problematic for those concerned when variations overtake their acceptable thresholds. Although often natural, these variations can be exacerbated by anthropogenic actions, like putting fish on a grill.

              Global changes are often reduced to temperature increases, illustrated in the media with alarming news about ice melting and forest fires. While many people thus omit the complex mechanisms behind this black box, the necessity of a more “polar bear’s” respectful way of life is commonly accepted. In order to better understand how to respect such adorable creatures, scientists need to investigate their relationships with the environment.

      Chapter 1: Shells under investigation

              In order to scrutinize these relationships, selected species must be accessible, easy to catch/manipulate and in sufficient number. For instance, the study of the great white shark aggressivity over humans would require too many intern’s sacrifices. In response to this challenge, a valiant research team from Germany looked for the importance of these relations by studying in the Rhine a remarkable (body and soul), accessible, cheap and lovely species: Corbicula fluminea, a shell. This study is related to the mass mortalities events of this species, which occurred in the summer, especially in that of 2003. Their investigations aim to understand how these organisms are linked with their environment, and their reactions to changes.

      Chapter 2: Shells cooking in science

      Many tools exist to perform this type of search. Field searches can involve the scientist’s life (be bitten by a pigeon is a terrible experience…) and obstruct a long-term individual experiment. Now that researchers have selected the perfect organism, they must choose an appropriate way to analyse their problem. For this shell, scientists chose to use a modelling approach, a method dark and full of terrors. More precisely, they modelled several aspects of the metabolism of this organism at different scales: individual and population levels, using respectively DEBM (Dynamic Energy Budget Model) and PSPM (Physiologically Structured Population Model). This method, widespread in ecology, consists to “simulate the annual growth in length and mass and the reproductive success under different environmental scenarios”. This approach is suitable because an organism can respond differently relatively to their peers. Such fact can be proved by looking at many places and species, humans included… Ultimately, scientists aim to better understand the complex relation between the energy available in the environment and its utilization by shells.

      Chapter 3: Corbicula’s deadly summers

      Heat waves are often responsible for changes that every scientist can observe on living organisms. For instance, it is known that coral reefs are affected by increased temperatures, as shown in an article published in “Free Radical Biology and Medicine”. Many other examples such as lobster’s behavioural response to boiling water could be developed. Regarding our shellfish, scientists found an interesting pattern comforting our previous remark: temperature causes shell’s mortalities… Oh wait, no, it’s more complicated.

      In fact, mass mortalities events were probably related to a melting pot of many events like temperature increases and/or starvation. Moreover, these situations are also in relation with individual conditions. Indeed, researchers hypothesized that a combination of factors (biotic and/or abiotic), usually non-lethal under regular summers, can be problematic at high temperatures. Unfortunately, models developed were not able to explain completely the observed mass lethal events.

      Chapter 4: Life is not so simple

      Researchers finally enhance the comprehension of population dynamics, enlightening its complex mechanisms. However, in such cases, wishing to be exhaustive is useless and unproductive, like politics. That is why scientists look for compromise between easy-to-use and complicated (highly realistic) tools. For example, the authors of the Corbicula’s study proposed that it could be interesting to test other parameters, such as parasitism.

      To put it in a nutshell (you got it, right?), things are not always what they seem to be, even in environmental studies. Main hypotheses are not always validated, and measures considered can be only a part of a more complex system, or sometimes even unappropriated. On the flip side, model’s development can help to understand the life cycle of organisms like Corbicula, thus helping to manage populations concerned.

      Cited study: Petter, G., Weitere, M., Richter, O., Moenickes, S., 2014. Consequences of altered temperature and food conditions for individuals and populations: a Dynamic Energy Budget analysis for Corbicula fluminea in the Rhine. Freshwater Biology 59, 832–846. https://doi.org/10.1111/fwb.12307

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    • Avoid predation or starvation: which strategy maximize rainbow trout juvenile survival?by Léa Bulon and Mylène Jury

      Published by Charlotte Recapet the September 9, 2019 on 7:12 AM

      Natural populations are increasingly exposed to a range of biotic stressors, such as predators, and abiotic environmental stressors such as environmental variations (seasonality -  Wingfield, 2013) or chemical pollution (Fisher et al., 2013). (We could think to grandma Margaret who throws away her bleach bucket directly into the river or grandpa George who loses all his plastic lures into the lack). The first year of life is complicated for all organisms because they are more sensitive to those kinds of stressors and their survival is highly impacted.

      In temperate zones, fry are subjected to high predation during the growing season and a nutritive resource deficit during winter. This is why juveniles need to find the best way to maximize their survival and make population viability durable through the time. Predators prefers a fry-up of little fish, it is why predation mortality is higher in small fish than large (Parkinson et al., 2004). However, growth itself may impose a significant energy mobilization which can drive trade-offs between growth and other metabolic processes. If you are really interested by the topic but not by fish, we recommend you to look at the article written by Mcleod et al., 2008, about birds.

      During winter, the metabolism needs some fuels like lipids and proteins to work because resources are often limited. Production of energy storage is energetically expensive, and energy contributes less to increasing their body-size.

      Is it better to allocate their energy into the growing season to avoid predators or into the lipid storage to survive during winter?

      Stephanie Morgensen and John R. Post, scientists from Canada, are been interested in this process. They led an experiment with juvenile rainbow trout (Oncorhynchus mykiss). They developed a mathematical model to determine the energy allocation strategy maximizing the first-year survival of rainbow trout.

      Rainbow trout juveniles are sampled from two sets of lakes in British Columbia in Canada. The first site is located on the Bonaparte Plateau and it corresponds to highly and cold lakes. The second site is located near the town of Merritt and it corresponds to low altitude and warm lakes. In warm lakes, the winter season is shorter than in cold lakes and there are more resources for juveniles.

      They found that juvenile growth is different between the two kinds of lakes: fish from the cold lakes growth more than fish from warm lakes. As we said before, production of lipid storage consumes more energy than growth and resources are more abundant in warm lakes. It is why, fish from warm lakes are more able to stock and fish from cold lakes, to growth. However, fish do not follow only one strategy. Indeed, they grow during the first part of the non-winter season and then they put their energy into the lipid storage to survive during winter. This switch between the strategies is controlled by environmental conditions and determined trout survival during winter.

      The juvenile survival trade-off influencing by environmental conditions such as temperature and resource availability would be important to understand population viability with the evolution of environmental conditions. Rainbow trout has been introduced into many streams and water bodies for recreational fishing because they are easy to catch and quite combative (fishing federation). They constitute an important economic interest it is why, it is one of the most studied species by biologists (INRA). This may lead to management measures to improve pisciculture conditions or to instore fishing quotas and a minimum size of capture. It could be also interesting to know if energy allocation strategies affect physiological processes like growth or reproduction.

      And you what would you choose to survive during winter?

      Cited study: Mogensen, S., & Post, J. R. (2011). Energy allocation strategy modifies growth–survival trade-offs in juvenile fish across ecological and environmental gradients. Oecologia, 168(4), 923–933. doi:10.1007/s00442-011-2164-0

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    • A damned energy loss for migratory fishes: dams!by Manon Salerno

      Published by Charlotte Recapet the June 10, 2019 on 9:42 AM

      Many species of fish grow in the sea and breed in rivers. These migratory fish are called anadromous. When a migratory fish is ready to breed, it leaves the sea and up a river to lay watershed upstream. It will find the optimum conditions to reproduce and allow the development of its offspring. But to do so, they spend a lot of energy on the upstream and sometimes, obstacles like dams in their path does not make it easy for them. This is the case of American Shad in the Connecticut River in the United States. Since the 1970s, 4 hydroelectric dams have been built in the river. Even if they are equipped with fish ladders, these obstacles require the Shad more energy to cross them than if they were not present. We know energy availability can be a limiting factor in migration. Thus, in 1999, scientists wanted to understand energy management in these fish, especially when it is modified by the presence of such.

      Any organism needs energy to perform the movements / migrations necessary for its life cycle. When they are heading into a period that will not allow them to feed (overwintering, migration), some species store energy, such as the bear before hibernating. For American Shad, this stock has to be created before migration because it will not feed during this move. First, scientists have found these are subcutaneous lipid reserves and skin constitute a special tissue for energy storage, which is rather unusual. Salmon, for example, usually mobilizes lipids from muscles and viscera. In contrast, for migration, somatic tissues (red and white muscles and skin) provide about 90% of the energy required in shad.

      According to this study, crossing dams is expensive in energy, especially for females. In fact, American Shad is a species able to reproduce itself several times in its life, but if migration requires too much energy, it will only happen once. It is therefore easy to understand a multitude of dams can have an influence on the reproduction of these fish and therefore on population size, even if they are equipped with systems allowing fish to pass. Not to mention some fish do not even find the fish ladder. These are more likely to be stressed, eaten by predators such as birds, or competing with other fish and unlikely to breed.

      Although fish ladders are quite efficient at the upstream for the American Shad, it is sometimes not suitable for other species. In addition, the outmigration can also present risks of mortality (water retention, drop height etc ...). It is therefore essential to remove the dams for which their function is not provided anymore. But in the United States, the erasure of small dams often meets opposition from local communities. Even though many dams have been removed, they represent a strong historical or landscape value for the inhabitants, creating tensions between the supporters of the restoration and the local communities. This situation reminds the context existing in France, where the aesthetic and historical arguments are very powerful. Many dams are attached to mills and water plants of olden times are therefore seen as a "living historical landscape" very characteristic of their landscape. Because of the local character of each operation, an opposition not necessarily collective but influential and well directed, is enough to block some sites.

      Cited study: J. B. K. Leonard and S. D. McCormick (1999) Effects of migration distance on whole-body and tissue-specific energy use in American shad (Alosa sapidissima). Canadian Journal of Fisheries and Aquatic Sciences 56(7), 1159-1171

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    • Pesticides and the power of earthwormsby Orane Becheler

      Published by Charlotte Recapet the May 10, 2019 on 6:04 PM

      We know that our current high use of some pesticides is harmful for the environment. For example, the controversy begun several years ago (National Geographic News, 2013 and Actu Environnement, 2018), about the disappearance of bees and the use of pesticides. Many of us have heard about this. In this context, assessing a priori the impacts of pesticides on environment can be helpful. This is why, five UK scientists have developed a model to anticipate the impacts of pesticides on the physiology of one species of earthworm, Eisenia fetida (A.S.A. Johnston and al., 2014).

      Why is it important?

                    The impact of pesticides on the growth and the reproduction of earthworms can lead to a huge decrease of their density and maybe to their disappearance. However, these organisms are very important for the soil quality. They provide good aeration and mixing of soil (call bioturbation) making it easier to absorb and keep water. Moreover, they greatly contribute to the degradation of organic matter making it accessible to other organisms. Indeed, a study of Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA, 2010) shows that, in a month, 1.5kg of earthworms (approximately 7,500 worms) can consume 30 days’ worth of a two-person household. In this way, plants growth better on a soil with earthworms than one without. This can be a great axis of reflexion about our way to produce vegetables. So, simulated impact of a pesticides on an area before destroy its ecosystem is a really good thing. Furthermore, we can see the importance of earthworms through their utilisation to evaluate the biodiversity in a participatory protocol (OPVT).

      In the video below, we can see the mix of soil by the earthworm’ displacements. Earthworms played a significant role in bioturbation.

      How did they do it?

                    These five UK scientists built complex model, call an energy-budget driven ABM. It consists of an interlocking of two model types: a huge one, an ABM (Agent Based Model), which contain many simple energy budget models. The first one allows to model how the population will progress, in other words the population’s dynamic. The second type allows to model life cycle processes for each earthworm from specified local conditions. Maybe the following picture can help you to understand.

      What did they found?

                    The main results are a decrease of growth and reproduction for the use of two pesticides.


      Modelling dose-response curves of two pesticides on the growth and the reproduction of Eisenia fetida. Adapted from the article.

                   Pesticides tested in this study are copper oxychloride and chlorpyrifos. The first one is widely used as fungicide and repellent, is not biodegradable and is “toxic to mammals and most biodiversity” (IUPAC, 2018). The second one is a current insecticide, “moderately persistent in soil systems, […] is highly toxic to mammals, […] birds, fish[es], aquatic invertebrates and honey bees” and “is classified as a reproduction toxicant, an acetyl cholinesterase inhibitor and a neurotoxicant” (IUPAC, 2018). So, the use of these pesticides can have large consequences not only on earthworms’ populations and so modelling consequences on others species is great.

                    Another study, presented by the Institut National de la Recherche Agronomique (INRA, 2014), shows also a decrease of earthworm populations when the quantity of used pesticides increases and vice versa (Pelosi C. et al., 2013).

      They have input local conditions of experimental data from literature. Their outputs fit great with the literature’s results, for non-toxic environments and for toxic ones, both individual life cycle processes and population dynamics.

      What is good and what is not?

                    Their model seems extremely complete because they incorporate varying food availability, use three steps of life with different parameters, for the adult stage they consider each step of processes under different feeding conditions and they consider interactions between individuals.

      In the ABM, they use a model landscape of 0.01 m2 patches of soil. It’s 10 cm2. I find this very small for a model which would simulate what it’s happening in the field. Moreover, further work is required to apply this approach to others species, maybe more ecologically relevant, and to implement the “heterogeneous distribution of chemicals in the soil and their degradation with time”. But this model can be useful to help to extrapolate data from laboratory to field or from species to species.

      Cited study: A.S.A. Johnston, M.E. Hodson, P. Thorbek and al. (2014) An energy budget agent-based model of earthworm populations and its application to study the effects of pesticides. Ecological Modelling 280, 5-17.

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    • A new approach of modeling dissolved organic matter release by phytoplankton. Is it an improvement?by Bastien Mourguiart and Thomas Panarotto

      Published by Charlotte Recapet the April 12, 2019 on 6:53 PM

      Phytoplankton is playing key roles in marine ecosystems. These microscopic plants are known, in particular, to be a part of the “Biological Pump”. Using photosynthesis as metabolism, it fixes carbon of the atmosphere to produce energy. This process reduces atmospheric concentration of CO2 and limits the greenhouse effect. It also produces oxygen indispensable to the life of many organisms.

      Phytoplankton forms the basis of the marine food chain. Autotrophic organisms, they convert sunlight energy into chemical energy (food). This food constituted by molecules with carbon (organic matter) can pass directly along the food chain when zooplankton eats the phytoplankton and in turn are consumed by larger animals such as fishes, whales, squids, shellfishes and birds. Organic matter (OM) can also be released by phytoplankton in a dissolved form named dissolved organic matter (DOM). Organic matter can then be absorbed by bacteria and enter the main food chain when bacteria are eaten by zooplankton.


      Marine food web

      Heterotrophic prokaryotes (all animals) use carbon contained in DOM as a major source of energy.  So, products excreted by phytoplankton are really important in the functioning of marine ecosystems and understand how DOM is released in the environment is essential.

      Livanou et al. present in their article “A DEB-based approach of modeling dissolved organic matter release by phytoplankton” a new model to calculate DOM release by phytoplankton. They apply Dynamic Energy Budget (DEB) theory on phytoplankton cells for that. In this study, the metabolism theory leads to describe DOM fluxes, based on assumptions about energy uptake, storage, and utilization of N and C. The authors are mainly interested in how DOM is excreted by phytoplankton under different nitrate concentrations.

      They calibrate and test the goodness of fit of the model using past laboratory data. In this previous experiment, others scientists (Flynn et al. 2008), measured DOM released by one species of phytoplankton with two phase of nutrient concentration: one with enough nitrate for all the individuals and one with nitrate in limitation. The results of DEB-Model fit well to experimental data according to Livanou et al. even it does not explain all the information: in the figure below, lines (the model) do not fit exactly the points (experimental data).


      Figure 2 in Livanou et al.

      To conclude, they explain quickly that their model permit to describe how DOM is released. In no N-limitation condition, passive mode is used and DOM excreted is more accessible for bacteria. For N-limitation condition, DOM released cannot be used by bacteria and it tends to accumulate.

      This study is maybe a step forward in comprehension of phytoplankton physiological mechanisms. However, in our opinion, it is not really useful to improve our understanding of energetic flows in the oceans. Moreover, the model was calibrated for only one of the thousand species of phytoplankton existing in nature. It should be calibrated for others species to catch up more processes which can change between species. The model can be more accurate catching up all the processes in this particular species too: the fitting test shows some differences from the experimental data (Figure 2). There is also limiting by the fact that only one nutrient is used as limiting nutrient: in reality, there can be more (Moore et al. 2013). To summarize, it needs very lot of work on this model to employ it in real ecosystems and be an improvement.

      Cited study: Livanou E. et al. (2019). A DEB-based approach of modeling dissolved organic matter release by phytoplankton. Journal of Sea Research 143, 140-151.

      Other references:

      Flynn, K. J., Clark, D. R., and Xue, Y., (2008). Modeling the release of dissolved organic matter by phytoplankton, J. Phycol., 44, 1171–1187, https://doi.org/10.1111/j.1529- 8817.2008.00562.x

      Moore, C. M. et al. (2013). Processes and patterns of oceanic nutrient limitation. Nature geoscience, 6(9), 701.

      Image source: Maggy Wassilieff, 'Plankton - Animal plankton', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/en/diagram/5137/marine-food-chain (accessed 8 February 2019)

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    • Identifying the optimal depth for mussel suspended culture in shallow and turbid environments.by Yann Godard and Louna Riem

      Published by Charlotte Recapet the February 1, 2019 on 4:52 PM

      Bivalve aquaculture is commonly carried out in shallow water where there is an important influence of winds, tide and currents. These factors can lead to the remobilization of particulate matter which is an important source of food for bivalves. However, the concentration of the particulate matter in water can be minimized by the filtration capacity of high density cultured bivalves. In order to improve the productivity of cultured bivalves, it is important to take into account these different parameters. Indeed, it will help to know where is the best place for bivalve’s growth.


      Skive Fjord mussel farms - https://northsearegion.eu/watercog/pilot-projects/skive-fjord-dk/

      A study conducted in a Fjord in Denmark suggests that the TPM (Total Paticulate Matter) in the environment of culture is very important for the growth of mussel. The autors have built two models to understand the mechanism:

      • The first model try to give a pattern of the vertical distribution of resuspended materiel by including, among others, the particles concentration at 1m above the seafloor
      • The second model allows seeing the growth mussel at different height in the water column and calculates growth rates. This is made under different scenario of food availability.

      Both of these models allow determining the optimal localization of mussel in the water column for the better production.

      Firstly, the authors have determined the characterization of seston in the long-term and in the short-term. They observe that there was important correlation between wind and TPM but with a lag of 9 hours. Thus, they say that the remobilization of particles is not depending of the wind in the farm but of the remobilization in another place in the fjord for the short-term seston characterization. These particles are then transported by water current until the Fjord. Moreover, a correlation is also observed between the chlorophyll concentration and the TPM but not between the water velocity and TPM.

      For the long-term, they were able to highlight that the repartition of seston, and particulary phytoplankton in the water column was not homogeneous. There is a difference in concentration at the bottom and at the top with more phytoplankton at the surface (because of the lightening).

      Secondly, the authors wanted to characterize the growth of mussels under different conditions of availability of food with the hypothesis that the concentration of phytoplankton is homogeneous in the water column. The results say that in reality, there is more phytoplankton in the surface, then, the growth in the top is not very well implemented in the model. They conclude that it is important to consider the position of bivalves in the water column for an optimal growth.

      The dynamic energetic budget model shows that it is important to have a lot of phytoplankton and less detritus in order to get a better growth whatever the position of the culture. Moreover, this model allows showing that the variation of growth between the top and the bottom is only 2.6% which is negligible. They conclude this part by suggesting that “The reduced impact of height above the seafloor on mussel growth is related to the small contribution of resuspended material compared to the high background concentration of detrital matter”.

      This study takes place in a Fjord where the conditions are highly variable (changes in the tide, current, wind…). This is not implemented in the model. Therefore, it could be interesting to add some hydrodynamics parameters in the model in order to adjust it. Moreover, to improve the model, it would be wise to include some biological mussel parameter like the energetic costs of pre-ingestive sorting and pseudofaeces production. This model could be experimented in different places and different moment to validate it.

      Cited study: Filgueira, R., Grant, J., and Petersen, J. K. (2018). Identifying the optimal depth for mussel suspended culture in shallow and turbid environments. Journal of Sea Research 132, 15-23.

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    • Global change and climate-driven invasion of the Pacific oyster along European coasts: a bioenergetics modelling approachby Mélanie Gouaux and Lise Guégniard

      Published by Charlotte Recapet the January 8, 2019 on 3:20 PM

      Environmental changes such as seawater warming, and coastal eutrophication have an impact on breeding, larval survival and recruitment of marine benthic species. Global change induces changes in the natural distributions of native species and facilitates the spread of non-native species. Nowadays, the spread of non-native species in marine ecosystems around the world is one of the most serious environmental concerns. In receiving ecosystems, consequences of biological invasions are readily identifiable when invasive species are ecosystem engineers such as polychaetes or bivalves.

      Scientists of the French Research Institute for the Exploitation of the Sea and of the university of Nantes investigated how global change relates to the invasion of European coasts by a non-native marine invertebrate, the Pacific oyster Crassostrea gigas.

      This species was introduced on the European coasts of the Atlantic at the end of the 19th century for shellfish culture purposes and is the main oyster species farmed in Europe today. In recent decades, the Pacific oyster has acquired invasive species status with the expansion of its biogeographic distribution along the northwestern European coast beyond its initial zone of introduction into sites breeding. Bourgneuf Bay on the French Atlantic coast was considered as the northern boundary of C. gigas expansion at the time of its introduction to Europe in the 1970s. From this latitudinal reference, variations in the spatial distribution of the C. gigas  reproductive niche were analysed along the northwestern European coast from Gibraltar to Norway.


      A bed of Pacific oyster Crassostrea gigas in the Netherlands - Bas Kers - CC BY-NC-SA 2.0

      Mechanistic models are valuable tools for this purpose, and modelling approaches are useful for gaining a quantitative understanding of the effects of environmental changes on marine communities, and predicting their responses to projected climatic trends.

      The use of the IBM and DEB models has shown results at different scales, at the individual scale, at the Bourgneuf Bay scale and at the European scale.

      At the individual level, the results showed interannual variability of the dry flesh mass (DFM). A loss of DFM is explained by a spawning event. There has been a significant increase in DFM and the number of oocytes in recent years. To explain these results, they studied the relationship between the environmental conditions in late spring and the characteristics of the oyster. Then they achieved positive relationships between DFM and phytoplankton. Likewise, between the number of accumulated oocytes and phytoplankton. Here, phytoplankton seems to be the cause of this increase of DFM and the number of oocytes in recent years for this species of oyster. Here, phytoplankton seems to be the cause of this increase of DFM and the number of oocytes in recent years for this species of oyster. Moreover, according to the individual model, the higher the temperature of the sea surface, the earlier the clutches (June-July). While a cooler sea surface temperature will result in late laying (August-September).

      Then, they applied the same models to the bay of Bourgneuf. The results showed an increase in the temperature of the sea surface in the bay, but also the effects of the temperature of the water on the laying. Indeed, as at the individual scale, the high-water temperatures lead to prose spits and vice versa.

      Results at the European level showed a change in the geographic limit of spawning habitat, regardless of phytoplankton concentration. In 1986, the limit was located at the level of the Loire estuary with a south-north spawning gradient, earlier in the south of Europe. In 2003, this limit moved completely to the north of Europe. This change can be explained by the global warming of the waters.

      Other studies have highlighted other results. Indeed, using a Degree / day model, Ifermer has demonstrated the importance of the nutrient pool for egg laying. Indeed, in recent years, laying is actually late because of the low nutritional value of phytoplankton. The warming of the waters would therefore cause the loss of the oyster's nutrient pool and thus a delay in laying eggs.

      Cited study: Yoann, T., et al. (2016). Global change and climate-driven invasion of the Pacific oyster (Crassostrea gigas) along European coasts: a bioenergetics modelling approach. Journal of Biogeography 43(3), 568-579.

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    • Time and concentration dependency in the potentially affected fraction of species: The case of hydrogen peroxide treatment of ballast waterby Marie-Adèle Dutertre and Maud Hautier

      Published by Charlotte Recapet the December 10, 2018 on 4:32 PM

      Globalization and international trade made natural gates easier to cross for species. As a consequence, few species were able to travel long distance and settled in new habitats where they become invasive species.

      More than 80% of industrialized goods in the world are transported by the oceans in container ships. In many cases, container ships is discharged in the destination port and go back empty. Whereas, the structure of this kind of ship does not allow them to travel empty and with stability. This is for a problem of stability  that ballast exists. Since the 19th century, ballast with rocks was substitute with water. Before ships leave the port , water is loading in tank and at the destination port tanks are discharged.


      http://www.seos-project.eu/modules/marinepollution/marinepollution-c04-p05.fr.html

      Ballast water transport contribute to invasive species spreading. In order to fight against exotics species, waters ballast are treated with Hydrogen Peroxide (H2O2). But there is  a question : how to be sure that ballast water is effective and is not toxic for the marine environment ? In order to evaluate the environmental impact of the treatment, a study has been conducted. Three taxa has been chosen, among them, two crustacean, two algae and one rotifera : C. volutator, A. salina, E. costatum, D. teriolecta,  B. plicatilis. The authors of the study consider three dimensions : Hydrogen Peroxyde concentration, the effect of the Peroxide Hydrogen on organism and Hydrogen Peroxide exposure time. In the experiment, they made the tree dimensions varied and they considered as the final aim, the mortality, the immobility and the inactivation of the organism. The results are used in a mechanistic model which is based on the description of  Dynamic Energy Budget theory. The DEB theory consists of a simple set of rules that specifies how organisms acquire energy and building blocks from their environment to fuel their life cycle. It is used to rely the observed effects and the hydrogen peroxide concentration in the experiments. The DEB-tox model allows to determine ECx — Effect Concentration — : the concentration which induces a response of x% between the baseline and maximum after a specified exposure time ; and the HCx — Hazardous Concentration — : the concentration which is dangerous for x% of the population. Thanks to this values, it is possible to determine the PAF — Potentially Affected Population— with means the part of an ecosystem potentially affected by a drug concentration. The results show an interspecific response variability with means different interspecific H2O2 sensibility. Sensibility is a combination between time exposure and the concentration. The conclusion of the study is that the hydrogen peroxide is effective for treating ballast water.

      Concentrations, effects and time exposure were studied there. The choice of the five species is a wise choice as a result of the representativeness of a wide selection of sensibility which allows to extrapolate this results to other species and then estimate the effect of hydrogen peroxide treatment on other species present in water ballast. Whereas the aim of the study was to assess environmental risks of hydrogen peroxide treatment, and the obtained results here cannot be used to conclude regarding as the environmental risks.

      To assess more precisely the risk, it is important to consider the hydrogen peroxide degradation and its potential impact on marine ecosystem. The H2O2 is oxygenated water which would rapidly be decomposed : 2H2O2 => 2H2O + O2. In this case, the hydrogen peroxide would not impact the environment.

      Furthermore, sub-lethal effects are sufficient to reduce the viability of the organisms and for that, lower concentration of H2O2 and lower time exposure are sufficient. The purpose is to neutralize exotic species with lower environmental and economic costs. Moreover, in order to reduce again the hydrogen peroxide used quantity, other studies show the efficiency of using UV, Ozone, and ultrasound for neutralizing species. The hydrogen peroxide treatment can also be used with alkaline water which allows to obtain the same result with lower concentration and time exposure.

      An other option is to establish regulated areas for discharging and to filter and to purify ballast water before discharging in the environment.

      Cited study: Smit, M. G., Ebbens, E., Jak, R.G., and Huijbregtst, M.A. (2008). Time and concentration dependency in the potentially affected fraction of species: The case of hydrogen peroxide treatment of ballast water. Environmental Toxicology and Chemistry 27(3), 746-753.

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    • Use of dynamic energy budget and individual based models to simulate the dynamics of cultivated oyster populationsby Maxime Rochet and Jean-Baptiste Valerdi

      Published by Charlotte Recapet the October 8, 2018 on 12:45 PM

      This paper deals with a test of Dynamic Energy Budget (DEB) apply for predictions of the oyster Crassostrea gigas production in Thau Lagoon. The DEB model is based on physiological and environmental parameters, he predict the growth at indivual level. In the case of oyster production the prediction must be applicate at the cohort levels, its why they choose to integrate the DEB model into a population dynamics concept. Population model choose its the IBM (Indivifual Based Model) method, the equations are used for the predict the harvested production and the stocks in place (total number of individuals).  The advantage of this integration its to assess the effect of ecosystem changes on oyster production.


      Oyster farming in the Thau Lagoon - Olivier Pessin - CC BY-SA 3.0

      The models recently used (DEB) have been compared with a more common prediction tool. The partial differential equation (PDE) are empirical equations used for the growth prediction between different class and simulate by individual total mass. This equation are more straightforward than the DEB-IBM models but they use only a single variable to represent individual growth. The DEB model integrate two variable of calibration, the other parameters of the differents equations were estimated from independent datasets using comprehensive studies of oyster growth and ecophysiology under controled conditions. The calibrated parameters are the chlorophyll a concentration proxy of the phytoplacton biomass (principal food of oysters) and the température linked to assimilation and maintenance rates. This technique modelise by this way the indivdual capatcity of food assimilation and the allocation of energy between energical reserve, structural tissues ans reproductive structure and maintenance. To be more likelihood a growth variability showing variability between individuals have been implanted. Some variability have been implanted into the prediction of PDE method and the DEB-IBM model. This variability was integrate by diffusion to reproduce the variability between individual growth in the PDE and by Xk (half saturation coefficient) variability in the DEB-IBM case.

      The results of the differents simulations have proved a good capacity for the DEB-IBM model to predict the stocks and the harvest productions. The data estimated are close to the observed. He have to advantages to be generic, easy to etablish by the low number of measurables parameters. With the results showed in the study (see figure below) his capacity to take account of the environmment variables have been proved too . The limits are detectable in his sensivity to the variability and the large number of parameters estimated can induce in error.


      From Bacher & Gangnery 2006.

      The comparison of the two models have show the effect of the variability in the predictions values. The values predicted by the DEB-IBM model look closer to the observation than the PDE predictions. For exemple the harvestes productions have been estimated earlier by the PDE method than the DEB-IBM, so the modelisation of DEB parameters can influe strongly the dynamic population and the production previsions.

      Cited study: Bacher, C., & Gangnery A. (2006). Use of dynamic energy budget and individual based models to simulate the dynamics of cultivated oyster populations. Journal of Sea Research 56(2), 140-155.

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    • Are vulture restaurants needed to sustain the densest breeding population of the African white-backed vulture?by Mikel Cherbero and Tom Laffleur

      Published by Charlotte Recapet the August 3, 2018 on 10:00 AM

      As obligate scavengers, vultures are entirely dependent on carrion. These last decades, carrion abundance has decreased in many areas. The two main causes of this trend are clearly identified. Natural habitat destruction reduces wild animal carrion abundance, which is the natural resource of scavengers. At the same time, the modification of agricultural practices, essentially the generalization of carcass rendering, has reduced the availability of cattle carrion. These factors have led to a negative trend on scavenger populations. This is especially the case in Africa, where most of avian scavenger species are now endangered. African savanna ecosystems were originally rich in avian scavengers, but most of the species are actually endangered.


      White-backed vultures feeding on zebra carrion - Bernard Dupont - CC BY-SA 2.0

      In this study, authors model the carrion ecology of an ecosystem in Swaziland which is home to the densest breeding population of the African white-backed vulture (Gyps africanus), a critically endangered species. They also study other threatened scavenger species of Swaziland: white-headed vulture (Trigonoceps occipitalis), Nubian vulture (Torgos tracheliotos), marabou stork (Leptoptilos crumenifer), tawny eagle (Aquila rapax) and bateleur (Terathopius ecaudatus). The purpose of this work is to better understand the feeding activity of the white backed vulture and to modelize population trends for these six species (using life-history traits and modelization of carrion availability), and based on these results authors discuss if the establishment of vulture restaurants would be beneficious.

      They first calculated the foraging radius (r) of the white-backed vulture, based on the Foraging radius concept theory. The foraging radius represents the radial distance from the nest in which the energy inputs are greater than the costs of feeding and needs of the vulture and its litter. This theory is adapted to this species, because vulture always comes back to the nest after feeding. They compiled available bibliography and collected data on metabolism and life-history parameters of the species. Using this data, they applied a model created with the same purpose by Ruxton & Houston in 2002 for the Ruppell’s vulture (Gyps rueppellii), which is phylogenetically and ecologically close to the white backed vulture.

      The results shows that the foraging radius is 260 km in the main part of the year. This radius is large, vultures can feed in neighboring countries (South Africa, Mozambique), it implies an international cooperation in the management of these endangered populations. A positive aspect is that individuals can spread over large area, so the studied population can form or sustain other populations. On the other hand this radius is much greater than the natural reserve surface, thus vultures can be exposed to several risks, like poisoning, when they are feeding. When vulture have to feed a chick, energy needs are logically greater so the foraging radius is reduced to 40 km. Carrion availability is more problematic during this period, which should therefore be targeted if vulture restaurants are setted up.

      Using novel Population Dynamics P-Systems, they show that carrion provided by wild ungulates biomass is currently enough to sustain this vulture species. According to the model, white-backed vulture population will continue increasing in Swaziland, and will pass from approximately 300 pairs to more than 500 in twenty years. The other studied avian scavenger populations will follow the same trend, but are far less abundant than white-backed vulture. The model shows also that three main species are composing vultures’ food: the Impala (Aepyceros melampus), the blue wildebeest (Connochaetes taurinus) and the plains zebra (Equus burchelli) represent 55 % of total carrion.

      However, in light of the forecasted population increases, food will become a limiting factor. This is particularly true for the period from November to April, for which the model show a carrion deficit. During this period African vultures are not breeding so they can go far away to feed themselves. But the model also shows a carrion deficit during the breeding season after five to thirteen years of simulation. This lack of food resources can be considered as a natural limiting factor. According to the model, the area has probably reach its maximum carrying capacity after twenty years.

      To conclude, authors suggest that setting up supplementary feeding stations in Swaziland should be seriously considered, especially during the breeding season. Good managed restaurants would have several advantages : secure the viability of the population and thus increase its capacity to act as a source population, avoid poisoning risks and create the opportunity to capture and tag vultures. This last point would allow to improve knowledge about the avian scavenger species, necessary for a more effective conservatory management.

      Cited study: Kane A., Jackson A.L., Monadjem A., Colomer M. A., Margalida A., 2015. Carrion ecology modelling for vulture conservation : are vulture restaurants needed to sustain the densest breeding population of the African white-backed vulture? Animal Conservation (18) 279-286.

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    • Temperature-dependent body size effects determine population responses to climate warmingby Alison Arraud and Laura Duran

      Published by Charlotte Recapet the July 5, 2018 on 1:55 PM

      Up to now, neither the size nor the stage of the individual were considered to studying the population responses to climate warming. On 2014, a scientific group proposed another way to understand the temperature effects on fish populations. They improved the interaction effects of temperature-dependence with the size and the stage of fish on their energetic thresholds responses. Energetic thresholds themselves act on the dynamic of stade-structured population (e.g. parr, smolt, adult).


      Flathead mullet (Mugil cephalus) - Roberto Pillon - CC BY 3.0 Unported

      Finally, this study found that increasing temperature could redistribute biomass across life stages and modify the regulation of the population by reworking the intra-specific competition. Other studies have shown that high temperature during ontogenesis can accelerate the development and growth of individuals or, give individuals of smaller sizes early maturation.

      This study points out the importance of taking into account the interactions between temperature and size-specific (maturing, reproduction, etc.) that will lead to a set of behavioral responses that have consequences on the structuring of a population. This is all the more important in the context of global warming.

      Cited study: Lindmark, M., et al. (2018). Temperature-dependent body size effects determine population responses to climate warming. Ecology Letters 21(2), 181-189.

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    • Can bioenergetic models help the re-introduction of the native Rio Grande cutthroat trout in a Southwestern headwater stream?by Emmanuel Bourgoin and Aurélien Callens.

      Published by Charlotte Recapet the May 16, 2018 on 1:47 PM

      Re-introduction of native species is far from being simple: many parameters must be accounted for! To illustrate that, we are going to take a closer look at a study made by Kalb and Huntsman (2017) on a stream in southcentral New Mexico which was deemed suitable for re-introduction of the native Rio Grande cutthroat trout (Oncorhynchus clarkii virginalis). Before re-introducing this species, researchers wanted to know if the habitat was able to sustain it. Thus, they evaluated habitat using resource selection functions with a mechanistic drift-foraging model to explain rainbow trout distributions. They studied rainbow trouts because they are present on the stream and are close relative to the Rio grande cutthroat trout, consequently all the results of this study can be extended to this native species.

       
      Rainbow trout - Timothy Knepp/U.S. Fish and Wildlife Service - Public domain

      Each month, the available habitat and foraging locations were evaluated along the stream. Foraging locations were defined as the location where they could observe a foraging fish. For each foraging site, the length of the fish was estimated and physical characteristics such as discharge, focal velocity (current velocity at the head of the fish), depth, cover distance and temperature were measured on the exact fish location. These parameters were also measured on the available sites. Macroinvertebrate drift was estimated on all the locations (available and foraging). All these parameters were used in bioenergetic models which allow the researchers to estimate all the intakes of the fish (net energy intake, energy assimilated…) and all the costs associated with foraging (capturing a prey, swimming…).

      First, they observed that macroinvertebrate drift was strongly season- and temperature-dependant with high values in summer and fall and low values in winter and spring. Moreover, as we must expect it, water temperature, depth and discharge were found to be seasonal parameters too. Secondly, models identified the depth as the most limiting factor for habitat selection: trout of all ages preferred habitat location with a greater depth.  The most interesting thing about the models is that they can show the characteristics of the chosen habitat according to the age of the trout and the season. In fact, they showed that during the winter the smaller size-classes were more likely to choose a position closer to cover. Additionally, they highlighted that spring was the season with the greater energy intake for all the size-classes expect the 4+. Finally, drift-foraging models identified that 81% of observed trout selected positions could meet maintenance levels throughout the year and 40% of selected habitats could sustain maximum growth. Despite these last observations, the larger size-classes were energetically more limited throughout the year.

      This study showed that trout population prefers deep pool habitats with slow moving water and that this stream was able to sustain a great population of rainbow trout and could consequently sustain a great native population of Rio grande cutthroat trout. However, authors warn us about the risk of hybridization and interspecific competition and suggest removing the non-native fishes first.

      To answer the question in the title: yes, bioenergetic models can help to re-introduce a native species in a given environment. Nonetheless, this example is really specific: author had the chance to find and study a close relative to the native trout in the stream! The main thing to remember is that bioenergetic models give a lot of useful information on how a species uses an habitat and must be taken into account (if applicable) in the management of species.

      Cited study : Kalb, B. W., Huntsman, B. M., Caldwell, C. A., & Bozek, M. A. (2018). A mechanistic assessment of seasonal microhabitat selection by drift-feeding rainbow trout Oncorhynchus mykiss in a Southwestern headwater stream. Environmental Biology of Fishes, 101(2), 257-273.

       

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