Tag Archive for: Modeling

Modeling reproductive traits of an invasive bivalve species under contrasting climate scenarios from 1960 to 2100

Mélaine Gourault, Sébastien Petton,Yoann Thomas, Laure Pecquerie, Gonçalo M. Marques, Christophe Cassou, Élodie Fleury,Yves-Marie Paulet et Stéphane Pouvreau

HIGHLIGHTS

  • The DEB model available for the Pacific oyster was applied in a new coastal environment: the bay of Brest (France).
  • This version was successfully calibrated using a new dataset covering 6 years (from 2009 to 2014) of field monitoring.
  • The model successfully predicted in detail the complex reproductive processes of C. gigas, especially its spawning behavior.
  • Hindcasting and forecasting simulations of the reproductive phenology of C. gigas were performed using IPCC scenarios.

ABSTRACT

Identifying the drivers that control the reproductive success of a population is vital to forecasting the consequences of climate change in terms of distribution shift and population dynamics. In the present study, we aimed to improve our understanding of the environmental conditions that allowed the colonization of the Pacific oyster, Crassostrea gigas, in the Bay of Brest since its introduction in the 1960s. We also aimed to evaluate the potential consequences of future climate change on its reproductive success and further expansion.

Three reproductive traits were defined to study the success of the reproduction: the spawning occurrence, synchronicity among individuals and individual fecundity. We simulated these traits by applying an individual-based modeling approach using a Dynamic Energy Budget (DEB) model. First, the model was calibrated for C. gigas in the Bay of Brest using a 6-year monitoring dataset (2009–2014). Second, we reconstructed past temperature conditions since 1960 in order to run the model backwards (hindcasting analysis) and identified the emergence of conditions that favored increasing reproductive success. Third, we explored the regional consequences of two contrasting IPCC climate scenarios (RCP2.6 and RCP8.5) on the reproductive success of this species in the bay for the 2100 horizon (forecasting analysis). In both analyses, since phytoplankton concentration variations were, at that point, unknown in the past and unpredicted in the future, we made an initial assumption that our six years of observed phytoplankton concentrations were informative enough to represent “past and future possibilities” of phytoplankton dynamics in the Bay of Brest. Therefore, temperature is the variable that we modified under each forecasting and hindcasting runs.

The hindcasting simulations showed that the spawning events increased after 1995, which agrees with the observations made on C. gigas colonization. The forecasting simulations showed that under the warmer scenario (RCP8.5), reproductive success would be enhanced through two complementary mechanisms: more regular spawning each year and potentially precocious spawning resulting in a larval phase synchronized with the most favorable summer period. Our results evidenced that the spawning dates and synchronicity between individuals mainly relied on phytoplankton seasonal dynamics, and not on temperature as expected. Future research focused on phytoplankton dynamics under different climate change scenarios would greatly improve our ability to anticipate the reproductive success and population dynamics of this species and other similar invertebrates.

Figure 4: Oyster growth and spawning simulations obtained by the DEB model compared with observed data from 2009 to 2014 (DFM = Dry Flesh Mass). Observed DFM is represented by black dots with standard deviation bars (n = 30). Grey lines represent individual growth trajectories simulated by the model. The dark red bold line represents the mean of the 30 trajectories.

REFERENCE

Gourault, M., Petton, S., Thomas, Y., Pecquerie, L., Marques, G.M., Cassou, C., Fleury, E., Paulet, Y.-M., & Pouvreau, S. 2019. Modeling reproductive traits of an invasive bivalve species under contrasting climate scenarios from 1960 to 2100. Journal of Sea Research 143: 128–139. doi:10.1016/j.seares.2018.05.005.

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Adaptive physiological and behavioural responses of organisms to multiple environmental stresses

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observation, experimentation and modelling

One of the great strengths of the PANORAMA team lies in the study of the physiological and behavioural responses of marine organisms to environmental constraints, whether of biotic or abiotic origin. The team strives to understand the effects of factors related to climate change (warming, acidification, hypoxia, nutritional constraints) and/or emerging pollutants on different species present mainly in coastal areas, in a monofactorial or multistress manner. In particular, it is developing approaches in ecotoxicology aimed at studying, on different models, the impact of micro- and nanoplastics, for which our laboratory is a precursor, or that of toxic microalgae, which also represents one of the laboratory’s strengths, or even that of diffuse pollution. We have exceptional structures and experimental and observation means that allow us to monitor the effect of these disturbances and contaminants, in large volumes and over the entire life cycle of the organisms: gametes, embryos, larvae, juveniles and adults. Thanks to this, we also understand the inter- and trans-generational effects of contaminants, pollutants, toxic microalgae and their toxins. Our experimental approaches are complemented by parallel studies in the natural environment where observational monitoring (e.g. monitoring of toxic microalgae blooms) and in situ experiments (e.g. caging experiments) are carried out. Our laboratory is very present in Brest, in the framework of sustained collaborations with CEDRE and ANSES, but also at the national level, with active participation in the GdR Aquatic Ecotoxicology, and the animation of the GdR PHYCOTOX and the GdR “Polymers and Oceans”. Our approach integrates all levels of biological organisation thanks to the new “omics” approaches in ecotoxicology, in association with cell biology, histology and eco-physiology measurements. We complete this coupling of observation and experimentation with modelling in conjunction with the “Coupling” Transverse Axis and the modellers of the DISCOVERY team.

New insights into trophic ecology

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Understanding how ecosystems function depends on our ability to identify the pathways by which energy and matter move through communities. This description is complicated in the marine environment by (1) the microscopic nature of the sources ingested by many organisms, (2) the spatial and temporal variability of the diet of organisms, (3) the high mobility of many species, which have the ability to find food in many different habitats, and (4) the highly opportunistic nature of many species from a dietary perspective. Understanding trophic relationships within ecosystems thus requires our ability to study these relationships empirically in the natural environment, to describe the forcing variables via experimentation, and to understand the consequences, from the organism to the ecosystem, via modelling approaches. In this context, LEMAR has undergone strong development over the past few years with the recruitment of researchers, teacher-researchers, engineers and technicians, and the development of analytical platforms giving it an unrivalled capacity in France in the field of isotope and lipid analysis applied to the marine environment, as well as in the field of bioenergetic and ecosystem modelling. These approaches are now used in all marine environments, coastal and offshore, polar, temperate and tropical, on numerous biological models and habitats, and will continue to develop over the next few years; they will provide new perspectives for understanding the functioning of marine ecosystems and organisms.

Influence of diatom diversity on the ocean biological carbon pump

Abstract

Diatoms sustain the marine food web and contribute to the export of carbon from the surface ocean to depth. They account for about 40% of marine primary productivity and particulate carbon exported to depth as part of the biological pump. Diatoms have long been known to be abundant in turbulent, nutrient-rich waters, but observations and simulations indicate that they are dominant also in meso- and submesoscale structures such as fronts and filaments, and in the deep chlorophyll maximum. Diatoms vary widely in size, morphology and elemental composition, all of which control the quality, quantity and sinking speed of biogenic matter to depth. In particular, their silica shells provide ballast to marine snow and faecal pellets, and can help transport carbon to both the mesopelagic layer and deep ocean. Herein we show that the extent to which diatoms contribute to the export of carbon varies by diatom type, with carbon transfer modulated by the Si/C ratio of diatom cells, the thickness of the shells and their life strategies; for instance, the tendency to form aggregates or resting spores. Model simulations project a decline in the contribution of diatoms to primary production everywhere outside of the Southern Ocean. We argue that we need to understand changes in diatom diversity, life cycle and plankton interactions in a warmer and more acidic ocean in much more detail to fully assess any changes in their contribution to the biological pump.

 

Graphical abstract

Reference

Tréguer, P., Bowler, C., Moriceau, B., Dutkiewicz, S., Gehlen, M., Aumont, O., Bittner,L., Dugdale, R., Finkel, Z., Ludicone, D., Jahn,O., Guidi, L., Lasbleiz, M., Leblanc, K., Levy, M. & Pondaven, P. (2017). Influence of diatom diversity on the ocean biological carbon pump. Nature Geoscience 11, 27–37 (2017). doi:10.1038/s41561-017-0028-x

Tag Archive for: Modeling

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