Feeding ecology of a Mediterranean endemic mesopredator living in highly exploited ecosystems

Abstract

Knowledge of marine predator trophic ecology is essential for defining their ecological role and trophic position in ecosystems. Based on their trophic habits, sharks and batoids occupy higher and medium trophic levels in the food webs, although differences in the trophic preferences exist between species. They are important organisms in marine ecosystems by maintaining the species below them in the food chain and serving as an indicator for ocean health. In comparison to sharks, batoids usually receive less research attention, with very little diet information available. This is true of the speckled ray (Raja polystigma), one of the three endemic batoids in Mediterranean waters. Here, by combining analyses of stomach contents and stable isotopes, we examined the trophic ecology (dietary composition and trophic position) of this ray in the north-western Mediterranean Sea. We also compared its trophic niche with the trophic position of other sympatric elasmobranchs present in same marine ecosystem. The results revealed that R. polystigma mainly consumes shrimps and to a lesser extent crabs, fin-fish, cephalopods, polychaetes and, surprisingly, small demersal sharks. We also found that R. polystigma shows similar trophic position to other crustacean-consumer elasmobranchs such rays and small demersal sharks. The results of this study provide new insights into the ecological role of this endemic ray species in the Mediterranean Sea.

Keywords: Elasmobranchs; Endemic species; Mediterranean Sea; Stable isotopes; Stomach content; Trophic ecology.