Main factors favoring Mnemiopsis leidyi individuals growth and population outbreaks: A modelling approach

International audienceA population model of the marine invasive ctenophore species Mneniopsis leidyi (ML) including physiological and demographic processes has been included in the flexible-stoichiometry biogeochemical marine ecosystem model (Eco3M-MED). This model is used in order to define through several numerical simulations possible environmental windows favorable to ML adaptation and outbreaks in invaded habitats, such as the coastal areas of the Mediterranean Sea. One of the strengths of the ML model is that it delivers the functional response either expressed in terms of consumed individual prey or in prey biomass, however the prey are expressed, as individual abundance or biomass concentration. Numerical experiments were performed to test the functional response in various quantitative and qualitative diet conditions. Longer term experiments including starvation regimes were run to characterize the response of the ML population in terms of growth rate and dynamics.Our results firstly show that the required food conditions for ML outbursts, which involve combinations of food quality and quantity, should mainly be found in the most productive Mediterranean coastal areas, and more rarely in the open sea, and that variations in food concentrations may induce rapid outbursts or collapse of ML populations. Results also indicate that food concentrations directly impact reproduction, and that for a given fixed available prey biomass, ML abundance is maximum for the prey of richest nutritional value. As our model considers two levels of ecological integration, individual and population, it has been shown that the response to starvation or to recovery from starvation after food replenishment occurs at different time scales depending on the integration level.Then, different scenarios of global change have been simulated in order to analyze the inter-annual variability in ML population dynamics. Our model could reproduce typical 3 months ML blooms, which is also observed in nature, and it suggests that this is the result of a combination of species properties and environmental forcings. Our simulations also reveal that an increase in temperature promotes the occurrence of jellyfish outbreaks. Finally, the strongest forcing influence on ML dynamics is the reduction of fish competitors for food due to an increase in fishing pressure. This forcing significantly impacts not only the frequency of the outbreaks, but also ML accumulated population growth over a ten-year period. Finally, our simulations call for long-term (over at least a ten-year period) observations with a temporal resolution of one month or less