An overview of the ecological roles of Mediterranean chondrichthyans through extinction scenarios

Abstract

Fisheries, climate change, and habitat degradation are triggering the depletion of marine animal populations worldwide. The ecological impacts of the extinction of keystone species such as chondrichthyans can be far-reaching along the entire food web. Here, we first reviewed the trophic ecology of the 81 chondrichthyan species of the Mediterranean Sea through a literature search. We then compared prey composition among chondrichthyan species considering their taxonomic group, body size, and habitat. Finally, we represented the Mediterranean meta-web, emphasizing the chondrichthyan groups, using a qualitative network approach, and tested the vulnerability of the food web to selective removals of threatened chondrichthyan species by applying different extinction scenarios. We found trophic data for 53 species, which highlights the need to complement current knowledge gaps for many species. Diet dissimilarities between chondrichthyan taxa were detected, mainly due to the consumption of crustaceans and cephalopods. We found that large chondrichthyan species had a major contribution to the trophic dissimilarity and the omnivory of the food web when compared to small and medium-sized species. Conservation efforts within the Mediterranean chondrichthyan community may be particularly important for this group, as high levels of omnivory could moderate the occurrence of trophic cascades, while high trophic similarity can lead to less diverse ecosystems. This study provides a first overview of the ecological role of chondrichthyans in the Mediterranean and highlights the urgent research needed to increase the knowledge about these key species in the Mediterranean marine food web.