Oysters with a plastic flavor in your plates for your celebrations!by Léa Bascoul, Vincent Dumontet and Sophia Lestringuez
Published by the November 8, 2021 on 5:52 PM
For over half a century, global plastic production has increased exponentially. Plastics represent 50% to 80% of marine litter. Microplastics (MP) are derived from the degradation of larger plastic articles or directly produced as microparticles (< 5 mm). Oceans have a “funnel” effect concerning MP drained from rivers and streams, they concentrate pollution from fresh waters in the oceans. In pearl farming structures and equipment, the use of plastics is a source of pollution to the detriment of the lagoon ecosystem. Due to their ubiquitous and small dimensions, MP are likely to be ingested by many organisms and in particular by the oyster, Pinctada margaritifera (Figure 1), which is a species of ecological and commercial interest. So, the objective of the study is to assess the impact of these microplastics on the physiology of this oyster species from the pearl lagoon of Ahe atoll, in the waters of French Polynesia (Figure 2).
Figure 1: Pinctada margaritifera
Figure 2: Ahe atoll localisationIn order to assess the effects of these molecules, IFREMER from French Polynesia, recreated microcosms [1] where oysters are exposed to polystyrene microbeads. Indeed, polystyrene is one of the most widely used plastic polymers and the most found in marine ecosystems.
After two weeks of depuration, oysters, were divided into three treatments. For each, 24 oysters were exposed to polystyrene solutions for two months. These solutions were a mixture of polystyrene microbeads of different diameters (6 and 10 μm) at equal weight. A control was carried out without exposure to polystyrene. Each tank, kept homogeneous, was exposed for 12 hours a day to light and the physico-chemical parameters were kept constant. The microplastic solution was injected continuously into the tanks associated with a mixed diet of two microalgae (Tisochrysis lutea and Chaetoceros gracilis).
Figure 3: Experimental exposure device of oysters to microplasticsDuring the experiment (Figure 3), various parameters, like oxygen consumption, were measured to assess the different energy expenditure of the oyster. Expenses related to food (ingestion rate and assimilation efficiency), to growth (the scope for growth defined from the energy budget and the shell growth rate) as well as those allocated to reproduction (characterization gonad [2] size and analysis of gametogenesis [3]) are quantified in each experimental group and compared to the control. The measurements were carried out on eight oysters per treatment after one month and then at the end of the experiment.
This experiment made it possible to demonstrate that at low MP concentrations, pearl oysters suffer adverse consequences for the sustainability of their populations. In fact, the metabolic responses of a stressed organism can lead to an increase in an individual's energy costs, forcing the organism to sacrifice some of its energy normally allocated to functions, such as growth or reproduction.
In this classical and standardized experiment, the oysters exhibited a significant dose-dependent reduction in the “scope for growth” without however modifying the shell deposit rate. On the other hand, although the ingestion rates of the microalgae were not affected by the microplastics, for an equal volume of filtered water the assimilation of the microalgae is disturbed by the presence of the microplastics and the energy supplied by food is lower. This is either linked to interference in assimilation processes in the digestive tract or to indirect competition between algae and microplastics.
The fact that metabolic (respiration) rates are not impacted suggests that the only possibility for the oyster to cope with a decrease in available energy is to modify its gametogenesis and / or its reproductive effort. However, reproduction in P. margaritifera is continuous and requires a lot of energy. The results of the study show that reproductive effort is not affected but that gametogenesis is strongly impacted. Thus “small holes” in the gonadal tubules [4] are observed in oysters exposed to microplastics. They could therefore be the start of the phagocytosis [5] of germ cells initiated to recover energy (Figure 4).
Figure 4: Impact on P. margaritifera metabolismIn a few words, the pearl oyster exposed to MP for a period of two months maintains its metabolism and its vital functions to the detriment of its reproduction, and therefore the sustainability of its future population.
This study could also serve as a model for the MSFD [6] Technical Group Marine Litter to assess the effects of microplastic litter in biota (D10C3), because the effects observed on Pinctada margaritifera in the lagoon of French Polynesia must be the same as on other filter feeding bivalves in Europe. The European Technical Group Marine Litter could thus propose a regulation of waste at the European level and not only at the level of the lagoon of French Polynesia.
The experiment results should support decision-making on plastic waste management measures in Polynesian lagoons, especially in atolls that have decades of pearl culture history without waste regulation or clean-up. This work would provide the necessary information to local authorities to regulate pearl equipment and establish a waste management policy such as the collection and recycling of this equipment.
The aim of the study was to measure the impact of microplastics on the metabolism of Pinctada margaritifera. The team of researchers therefore sought to artificially recreate different levels of pollution in the laboratory. This methodology is suitable because it aims to recreate the pollution conditions possibly encountered in natural environments. To measure these different levels of pollution, the experiment is carried out at different concentrations. As for the various parameters measured to assess energy losses, they make it possible to identify, in a non-invasive manner, the functions (growth and reproduction) "sacrificed" to cope with the loss of energy. They also allow us to see if this loss of energy had an effect on the metabolism of oysters. The parameters monitored therefore seem consistent for this study and could be used for similar studies on other bivalve filter-feeding organisms. Experiments using this protocol could be considered in fresh waters with other types of bivalves such as the mussel pearl (Margaritifera margaritifera). Also, this study can be evaluated with a direct approach on oysters from pearl farms and over several generations.
In several years, oyster populations on a global scale could be impacted by pollution from microplastics … so, if there are no more oysters, what will we eat with our white wine?
[1] smaller version of ecosystem
[2] an animal organ in which gametes (a haploid germ cell, such as a spermatozoon or ovum) are produced
[3] gamete formation process
[4] organs of gametes excretion
[5] cellular defense process, destructive function of phagocytes
[6] Marine Strategy Framework Directive
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Help! How do I manage my commercial oyster nursery?by Coline Arqué, Marylou Pourret and Robin Thibault
Published by 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?
Crassostrea gigas (Thunberg, 1793)- 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.
Mytilus edulis (Linnaeus, 1758)
Ruditapes philippinarum (Adams et Reeve, 1850)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.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.High throughput screening methods to assess pollutants effects: A relevant technique?by Alexandre Bijaye and Melody Fernandez
Published by the March 12, 2019 on 6:43 PM
The purpose of the paper written by Miller et al. in 2016 is to assess the effectiveness of HTS (High Throughput Screening) techniques to predict the effects of metal nanoparticles on a population of Isochrysis Galbana, a common species of phytoplankton.
High Throughout Screening is one of the newest techniques used in toxicology and which is planned to be implemented in biological and chemical sciences in the near future. Their technology is based on the analyzes of chemical compounds to be conducted in a short time. The affinity of biological structures which is related to the toxicity to be defined.
In this article, we’ll focus on nanoparticles: Engineered nanoparticles (ENPs) are actually an emerging form of metal contamination. These particles are widely used in biochemistry, engineering,… Four elements are studied in this paper: Ag, ZnO, CeO2 and CuO. The studied concentrations of each compound chosen were known to affect phytoplankton populations.
Silver nanoparticules (T. Theivasanthi/Wikimedia)The results showing a decline of the photosynthetic activity (PSII) are compared to the HTS tests results. DEBtox models are energycally and toxycodynamically balanced modelling techniques (DEBtox and TD) and are here used to evaluate the impact of ENPs.
First, the decline in photosynthetic activity is a good predictor. Phytoplankton are vulnerable to pollution, particularly because of their aptitude to accumulate contaminants. As a result, such a bioaccumulation can impact food webs integrity.
Isochrysis Galbana populations were cultured at 20°C in sterile seawater (at 34 per thousand of salinity). In these conditions, HTS techniques measured cellular lesions responding to a toxic agent, permitting here to measure the potential impacts of ENPs on organisms.
Four HTS tests were undertaken (based on the mitochondrial membrane potential, ROS occurence, (3) cellular efflux pump action and cell membranes permeability). These tests are based on fluorescence and cell health. The impact of metallic nanoparticles was also measured. However, the results obtained were not consistent enough to highlight responses to ENP exposure:
Non-HTS tests were performed by the measurement of the impact on photosynthetic efficiency. The metal concentrations were measured using the graphite furnace atomic absorption.
Fluorescence kinetics of chlorophyll was also measured with an amplitude modulated pulsed fluorometer. Then the maximum fluorescence yield was computed using WinControl Software. This the maximum fluorescence variation is assumed to be a measurement of the potential quantum yield of the PSII.
A clear decrease in the performance of the PSII was observed for all the ENP’s:
- A greater decrease was observed for ZnO
- Also, a notable decrease was measured for CuO, at low concentrations
- Finally, the presence CeO and Ag decreased the performances as well even though the decrease was the smoothest.
According to the authors, these results linked with the different dissolution rates that are specific to each compound. In this direction, Zn has a high dissolution rate, CuO and Ag dissolve very slowly and CeO has an undetectable dissolution rate.
As a conclusion by the authors, HTS methods can not be used to measure the impacts of metal particles because of their poor predictive power. So far, traditional ecotoxicological methods must be used.
With such results in mind, we also agree on this statement: the four tests led by the authors all brought different conclusions. As HTS methods rely on the affinity of biological structures which is often related to toxicity to be defined, the presence of cellular compensatory mechanisms could have masked cellular responses to ENPs expositions.
In conclusion, although HTS methods offer promising opportunities in the biological sciences (such as ecotoxicology), there are need for further investigation in this area before these techniques can be commonly adopted and used.
Cited study: Miller, Robert J., et al. (2016) Photosynthetic efficiency predicts toxic effects of metal nanomaterials in phytoplankton, Aquatic toxicology 183, 85-93.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Identifying the optimal depth for mussel suspended culture in shallow and turbid environments.by Yann Godard and Louna Riem
Published by 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.
This post is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.Global change and climate-driven invasion of the Pacific oyster along European coasts: a bioenergetics modelling approachby Mélanie Gouaux and Lise Guégniard
Published by 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 2.0Mechanistic 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.
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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 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 3.0The 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.
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