Lipids and fatty acids of cold-water soft corals and hydrocorals: a comparison with tropical species and implications for coral nutrition

Fatty acid (FA) markers are widely used for tracking trophic relationships in cold-water benthic ecosystems, but data on the lipid composition of soft corals and hydrocorals, which are important components of these ecosystems, are very limited. Lipid class and FA profiles of four soft coral families (eleven species) and one hydrocoral family (four species) from the northeastern part of the Sea of Okhotsk were studied for the first time and compared with their tropical counterparts. Among cold-water cnidarians, soft corals contained much more monoalkyldiacylglycerols but less triacylglycerols than hydrocorals. The lipid class profile of all azooxanthellate soft corals did not differ, whereas FA profiles of these corals from cold-water and tropical regions differed. The key FAs were arachidonic (20:4n-6) and eicosapentaenoic (20:5n-3) acids, followed by 24:5n-6 and 24:6n-3. Within the cold-water corals, a sharp difference in polyunsaturated FA (PUFA) profiles between Primnoidae species and other families (Nephtheidae, Paragorgiidae, and Acanthogorgiidae) was found. The high level of n-3 PUFAs (20:5n-3 and 24:6n-3) in Primnoidae and the high level of n-6 PUFAs (20:4n-6 and 24:5n-6) in other cold-water coral families indicated the substantial difference in a feeding behavior between these corals inhabiting the same biotope. Based on the FA markers, a dietary predomination of herbivorous zooplankton is assumed for Primnoidae. An opportunistic feeding on various food sources is supposed for other cold-water coral families studied. The lipid and FA profiles were found to be characteristic for tropical zooxanthellate reef-building and soft corals, azooxanthellate soft corals from tropical and cold-water regions, and Primnoidae among cold-water coral families.