Ecological role of Mediterranean chondrichthyans: trophic ecology and food-web modelling
Trabajo final presentado por Elena Fernandez Corredor para el Máster en Oceanografía y Gestión del Medio Marino impartido por la Universitat de Barcelona (UB) y la Universistat Politècnica de Catalunya (UPC), realizado bajo la dirección de la Dra. Marta Coll y del Dr. Joan Navarro del Institut de Ciències del Mar (ICM-CSIC).-- 49 pages, 15 figures, 4 tables, supplementary material ; Fisheries, climate change and habitat degradation are triggering the depletion of marine animal populations worldwide. In particular, the ecological impacts of the removal of keystone species such as chondrichthyans can be far reaching through the food web. In this study, we investigated the trophic ecology of the 81 Mediterranean chondrichthyan species occurring in the basin through a literature review. We found data for 50 species, which highlights research priorities for the future to complement missing information. Regarding the trophic ecology of studied species, prey composition was compared between taxonomic groups (Batoidea, Selachimorpha and Holocephali), habitats (pelagic and demersal) and sizes (small, medium and large). We found significant differences between taxonomic groups, with dissimilarities mainly due to crustaceans and cephalopods consumption between Batoidea and Selachimorpha. We then represented the Mediterranean meta-web by means of a qualitative modelling approach, putting emphasis on the chondrichthyan groups, with a resulting food web network topology of 73 nodes and 1335 trophic links. Finally, we used the qualitative food web representation to test seven extinction scenarios of chondrichthyans extinctions. We found out that large species, pelagic species and sharks had a major contribution to trophic dissimilarity of the ecosystem when compared to small and medium-sized species, demersal species and rays, respectively. Systems with the former species had also higher omnivory rates. Therefore, conservation efforts within the Mediterranean Sea chondrichthyan community seem to be especially important for these groups. This study provides a first overview of the chondrichthyans ecological role in the Mediterranean Sea marine food web and highlights the urgent need to improve available knowledge on these species and to adopt an ecosystem-based management approach in order to decelerate the depletion of chondrichthyans populations and prevent them from local extinctions, with important effects to the marine food web ; I was supported by a JAE Intro grant of the CSIC (JAEINT200_EX0215) that was extended with funding from the EU FutureMARES project. This work acknowledges the Severo Ochoa Centre of Excellence accreditation (CEX2019- 000928-S) and is a contribution to the European Union's Horizon 2020 research and innovation program under grant agreement No 869300 (FutureMARES project)