Catching the big picture of the Mediterranean Sea biodiversity with an end-to-end model of climate and fishing impacts

Abstract

The Mediterranean Sea is among the main hotspots of marine biodiversity in the world. Under combined pressures of fishing activities and climate change it has also become a hotspot of global change, with increased concern about the worsening status of marine exploited species. More integrated modelling approaches are needed to anticipate global change impacts in the Mediterranean Sea, in order to help decision makers prioritizing management actions and strategies, mitigating impacts and adapting to changes. Our challenge was to develop a holistic model of the marine biodiversity in the Mediterranean Sea with an explicit representation of the spatial multispecies dynamics of exploited resources under the combined influence of climate variability and fishing pressure. An individual-based ecosystem model OSMOSE (Object-oriented Simulator of Marine ecOSystEms), including 100 marine species (fish, cephalopods and crustaceans) and representing about 95 % of the total declared catches, has been implemented for the first time at a high spatial resolution (400 km2) and at a large spatial scale (whole Mediterranean basin). The coupling of OSMOSE to the NEMOMED 12 physical model, and to the Eco3M-S biogeochemical and low trophic level model has been achieved to build the OSMOSE-MED end-to-end model. We fitted OSMOSE-MED to observed and estimated data of biomass and commercial catches using a likelihood approach and an evolutionary optimization algorithm. The outputs of OSMOSE-MED were then verified against observed biomass and catches, and confronted to independent datasets (MEDITS data, diet compositions and trophic levels). Although some improvements are suggested for future developments, the model results at different hierarchical levels, from individuals up to the ecosystem scale, were consistent with current knowledge and observations on the structure, the functioning and the dynamics of the ecosystems in the Mediterranean Sea. All the modelling steps, from the comprehensive representation of key ecological processes and feedbacks, the careful parameterization of the model, the confrontation to observed data, and the positive outcome from the validation process, allowed to strengthen the degree of realism of OSMOSE-MED and its relevance as an impact model to explore the futures of marine biodiversity under scenarios of global change, and as a tool to support the implementation of ecosystem-based fisheries management in the Mediterranean Sea.

An End-to-End Model Reveals Losers and Winners in a Warming Mediterranean Sea

“…(3) A regional biogeochemistry model, Eco3M-S (Auger et al, 2011) that simulates at high-resolution the biogeochemistry cycles and the lower trophic level species (i.e., plankton) of the Mediterranean Sea. (4) A multispecies dynamic model (OSMOSE 1 ; Moullec et al, 2019), that represents at high-resolution the spatial dynamics of interacting high trophic level species in the Mediterranean Sea.…”

“…Finally, OSMOSE is driven one-way by the biogeochemistry outputs of Eco3M-S (i.e., by phyto-and zoo-plankton biomass). This end-to-end model is fully described in Moullec et al (2019), only a brief presentation of the structure and parameterization is given in the present study. Details on the OSMOSE model can be found at https://documentation.osmose-model.org/index.html.…”

“…OSMOSE covers the whole Mediterranean basin with a regular grid of 20 km × 20 km counting 6229 cells. It represents the Mediterranean food web from plankton production to main apex predators on the 2006-2013 period (Moullec et al, 2019). Ninetyseven high trophic level species (82 fish species, 5 cephalopod species, and 10 crustacean species, mainly shrimps) were modeled, accounting for around 95% of total declared catches in the region during the 2006-2013 period.…”

“…Ninetyseven high trophic level species (82 fish species, 5 cephalopod species, and 10 crustacean species, mainly shrimps) were modeled, accounting for around 95% of total declared catches in the region during the 2006-2013 period. Modeled species were selected according to their ecological and economic importance and Data Availability (Moullec et al, 2019). For this study, three amphihaline fish species (i.e., Alosa alosa, Alosa fallax, and Anguilla anguilla) were removed from the previous version of the model because their complex life cycle characterized by movements between fresh-water and salt-water has not been modeled as being influenced by climate change.…”

“…In this context, we used an integrated modeling chain including a high-resolution regional climate model, a regional biogeochemistry model and a food web model (Moullec et al, 2019) to project the potential effects of climate change on biomass and catches for a wide array of species in the Mediterranean Sea, by the middle and end of the 21st century under the high-emission RCP8.5 socio-economic scenario and "business as usual" fisheries management (i.e., current fishing mortality). With this modeling chain, primary and secondary production changes and spatial distribution shift of species induced by climate change were considered.…”