Fish biomass changes across mid-Pleistocene glacial-interglacial transitions in the eastern Mediterranean

Théo Sommeville

Studying the ecology and distribution of species in an ecosystem is essential to better understand their responses to environmental stresses, such as climate warming, and guide policy. The eastern Mediterranean marine ecosystem (EMME) has many endemic species that are particularly vulnerable to sea surface warming, especially in coastal areas. Yet, isolating the effect of climate warming on EMME can be complicated as this area is subject to many stressors such as anthropogenic impacts (tourism, noise pollution) and biological invasions. In this study, we identified and measured 2035 otoliths in order to calculate fish size and biomass in three different Pleistocene periods corresponding to glacials and interglacials.

The decrease in size of individuals and the increase in biomass during the MIS19 interglacial period was mainly driven by the Myctophidae family, which is the most abundant family in our samples. We hypothesized that these changes in size and biomass during the interglacial period were mainly due to a change in diet from the Myctophids that would have altered the balance of the marine food web.

Our work thus constitutes an important contribution to the future functioning of EMME and to the reaction of associated species still present in the area to the climate warming predicted by the Intergovernmental Panel on Climate Change (IPCC).