Trophic ecology of two cold-water coral species from the Mediterranean Sea revealed by lipid biomarkers and compound-specific isotope analyses

Scleractinian cold-water corals (CWC) act as key ecosystem engineers in deep-sea reef environments worldwide. However, our current understanding of their trophic ecology is still limited, particularly in understudied temperate oceanic regions such as the Mediterranean Sea. Hence, this study investigated the trophic ecology of the CWC Desmophyllum dianthus and Madrepora oculata by employing lipid biomarker techniques and compound-specific isotope analyses on coral tissues, suspended particulate organic matter (sPOM), and surface sediment sampled in a Mediterranean CWC habitat. CWC exhibited high contents of poly- and monounsaturated fatty acids (FA) (a parts per thousand yen49 and 32 % of FA, respectively) and cholesterol (a parts per thousand yen67 % of sterols), while sPOM and sediment samples were enriched in saturated FA (a parts per thousand yen44 % of FA) and sitosterol (a parts per thousand yen35 % of sterols). CWC contained some rare very long-chained polyunsaturated FA (> C22) and ergosterol absent in sPOM and sediment samples. Our results indicate that Mediterranean CWC mainly consume living food items, rather than detrital sPOM or resuspended sediment, and provide evidence for preferred feeding on omnivorous and carnivorous zooplankton. Overall, these findings provide new insights to the trophic ecology of two common CWC from the Mediterranean Sea.