Ecosystem modelling in the eastern mediterranean seathe cumulative impact of alien species, fishing and climate change on the israeli marine ecosystem

Resumen

Firstly, I reviewed modelling approaches that were used to assess the impact of invasive alien species (IAS) in aquatic ecosystems. According to the review, multispecies/ecosystem mechanistic models dominated the applications, with dynamic and non-spatial models being the most prevalent. Most of the models included an additional human stressor, mainly fisheries, climate change and/or nutrient loading. I summarised the main features of these applications and analysed their capabilities and limitations. Based on my conclusions, I reflected on future directions of development and applications of suitable modelling tools. The review showed that the Ecopath with Ecosim (EwE) modelling approach was frequently used to assess the impacts of already established IAS and highlighted its capabilities to forecast existing, emerging and potential new IAS. As a second step, I developed two static Ecopath ecosystem models using the EwE approach and representing the food web of the Israeli Mediterranean coast in 1990s and 2010s. I characterized the structure and functioning of the ecosystem and assessed past and current impacts of IAS and fishing. I then used the time-dynamic Ecosim module of EwE to fit the 1990s model to available time series of observations between both periods and to explore the historical dynamics of the ecosystem considering the effects of IAS, fishing dynamics and sea warming. Finally, the time-dynamic ecosystem model was used to analyse alternative future simulations of ecosystem change. Particularly, and after interacting with key stakeholders, I assessed the future effects of a new set of fishing regulations currently being implemented in Israel, future changes in sea temperature following IPCC (Intergovernmental Panel on Climate Change) scenario projections and the potential increases in IAS biomass. I investigated the impacts of the stressors separately, and then I combined them to evaluate their cumulative effects. Results from the static Ecopath models highlighted that the Israeli marine ecosystem, despite productivity differences, shared some structural and functional traits with other Mediterranean ecosystems such as the dominance of the pelagic domain in term of flows, the important role of detritus through low trophic levels and the importance of the benthic-pelagic coupling. In both time periods investigated, the same keystone groups were identified with the exception of European hake in 2010s, which showed a decline in its keystone role. This may indicate that hake lost its ecological role due to population declines. Most of the functional groups identified as keystone species were previously identified as keystones in other Mediterranean ecosystems, such as dolphins, large pelagic fishes, sharks and squids. The temporal dynamic Ecosim model indicated that trophic interactions, ocean warming and fishing were important drivers of the ecosystem dynamics. In general, temporal biomass trends revealed that native demersal predators and native medium trophic level fishes largely declined over time, while an increase over time of alien species was observed. Results from ecological indicators suggested a degradation pattern of the ecosystem over time. Future scenarios using the temporal dynamic Ecosim model showed overall potential benefits of fishing effort reductions in the future, and detrimental impacts of increasing sea temperature and increasing biomass of alien species. Cumulative scenarios highlighted that the beneficial effects of fisheries reduction could be dampened by the impact of increasing sea temperature and alien species when acting together. These results support the need for reducing local and regional stressors, such as fishing and biological invasions, to retain marine ecosystems within a “safe operating space” and ensure ecosystem resilience in an ongoing warming and impacted sea.