Trophic relationships and UV-absorbing compounds in a Mediterranean medio-littoral rocky shore community

Abstract : Organisms inhabiting shallow coastal ecosystems are potentially exposed to damaging levels of solar UV radiation. UV-sunscreen compounds such as mycosporine like amino-acids (MAAs) are a widespread biochemical strategy among many marine organisms to counteract UV stress. These molecules are produced through a metabolic pathway restricted to cyanobacteria, various algal groups and fungi. This study was designed to search for UV sunscreen compounds in benthic invertebrates of the Catalan medio-littoral rocky shore of the north-western Mediterranean Sea. The relationship between food sources and consumers was investigated using the stable isotope approach in order to elucidate the potential pathways of MAA transfer. The food web associated with the littoral Catalan rocky shore is characterized by a high level of functional complexity. The variability of δ13C and δ15N among and between trophic guilds provides evidence of the diversity of coexisting trophic levels and trophic pathways in a single habitat type. MAAs were present in all sampled metazoan species. We observed a higher MAA diversity in animals than in food sources. This may be explained by the incorporation of MAAs from several trophic resources, by the conversion of the MAAs acquired from the food or by translocation from a symbiont. The amount of MAAs in sea urchins was fairly low compared to other trophic groups. This cannot be explained by depletion of MAAs in their diets, and hence other UV-protective strategies may be more important. Complementary experimental studies should be performed to determine the ability of primary and secondary consumers to assimilate MAAs and convert these compounds