Coll Monton

Anthropogenic activities have caused significant shifts in species composition and abundances in marine ecosystems which translate into degradation of food-web structure. The Mediterranean Sea has been subjected to intense anthropogenic disturbance for thousands of years with high fishing pressure, habitat modification and pollution. Using data from two well-studied marine food webs in the Mediterranean Sea (North-Central Adriatic Sea, South Catalan Sea) we assembled species lists from two time periods (mid-late 1970s and mid-late 1990s) into “who-eats-whom” feeding networks to determine whether and how changes in species composition and biomass have affected 22 structural food-web properties. Our results indicate strong similarities between Mediterranean food webs and similar levels of degradation, suggesting that degradation has occurred prior to the mid-late 1970s. However, when comparing Mediterranean food-web properties with other published marine food webs (e.g. Caribbean, Benguela, US continental shelf), the Mediterranean showed the most advanced state of ecosystem degradation with lower trophic height, linkage density and connectance, lower omnivory, species involved in looping, trophic chain length and fraction of biomass at higher trophic levels, as well as higher generality and fraction of biomass at lower trophic levels. Robustness of food webs to simulated species removals indicated that the Mediterranean systems were among the most sensitive food webs, with higher numbers of secondary extinctions than either the Caribbean or US Shelf. Importantly, both ecosystem modelling approaches used in our analyses, the niche and ecopath model, delivered comparable results capturing fundamental components and changes of food-web structure.