Using traits to build and explain an ecosystem model: Ecopath with Ecosim modelling of the North Aegean Sea (Eastern Mediterranean)

摘要

The mass-balance-trophic-model Ecopath and its extension Ecopath with Ecosim is very popular for modelling marine ecosystems. In this work, a model of the marine ecosystem of the North Aegean Sea (eastern Mediterranean) was created, incorporating the use of biological traits in both building and explaining the model. For the former, data regarding a total of 19 biological traits concerning the biology, distribution, ecology and behavior were used for the definition of fish functional groups. Regarding model interpretation, the results were not only analyzed in the functional groups level but also regarding the composition of the resulting biological traits. In total, 41 functional groups were created for this model. Landings data and discards estimations of the year 1993 were used for the Ecopath component. Six different fisheries management scenaria, one retaining a business-asusual (maintenance of the status quo) approach and the others investigating changes in fishing effort for the period 2018-2033 were simulated with Ecosim. The simulation results indicated a reduction of pelagic species as well as of biological characteristics associated with them. Concurrently, an increase in the biomass of deep-living species and of relevant biological traits was observed. In general, no strong differences were documented among the various simulation scenarios with the exception of the species targeted by the individual fisheries whose fishing effort changed in each scenario and the associated traits. Significant findings pertain to the decrease of thermophilic traits like high optimal temperature and summer spawning in all fisheries management scenaria simulated. These could mitigate the opposite trend expected to be favored by climate change and the decrease of characteristics associated with the r-life strategy, possibly resulting in less resilient future fish communities. In addition, the negative trends of the biological traits that are anyway rare (e.g. low trophic level and small lifespan) may impact ecosystem functioning. The modelling approach used on this work could be adopted to model other marine communities (possibly also using traits for other ecosystem components) to provide interesting insights regarding anthropogenic effects on marine ecosystem functioning.