Fatty acid composition as an indicator of possible sources of nutrition for soft corals of the genusSinularia(Alcyoniidae)

Abstract

Fatty acids (FAs) composition of eight zooxanthellate soft corals,Sinularia leptoclados, S. flexibilis, S.aff.deformis, S. lochmodes, S. cf.muralis, S. densa, S. notandaandS. cruciatacollected in Van Phong Bay (Vietnam) were studied to identify possible origin of unsaturated FAs. The main FAs were 14:0, 16:0, 7-Me-16:1n-10, 16:1n-7, 16:2n-7, 18:0, 18:1n-9, 18:4n-3, 20:4n-6, 20:5n-3, 22:6n-3, 24:5n-6 and 24:6n-3. On the average, saturated, monounsaturated, and polyunsaturated FAs (PUFAs) contributed 35.6, 6.2 and 54.0% of total coral FAs, respectively. PUFAs of n-6 series predominated in all animals (n-6/n-3 > 1.6). The content of 20:4n-6 varied from 10.2 to 23.8%. The main n-3 PUFA was 18:4n-3 (on the average, 5.4%); the contribution of 20:5n-3 and 22:6n-3, typical PUFAs of marine organisms, was not more than 2.4 and 3.9%, respectively. InSinularia, PUFAs were produced by endosymbiotic dinoflagellates (zooxanthellae) and the coral host tissue, or obtained with food. Zooxanthellae can be considered as the source of C16PUFAs and 18:4n-3. The coral host synthesized 18:2n-7, 24:5n-6 and 24:6n-3 acids. The low content of 18:1n-7, saturated odd-chain FAs and saturated methyl-branched FAs indicated a negligible contribution of bacteria to total lipids ofSinularia. A comparison of the levels of diatom and dinoflagellate FA markers in coral and plankton lipids showed eukaryotic microalgae to play a secondary role in feeding ofSinularia. The high level of 20:4n-6 may be considered as an indicator of heterotrophic feeding ofSinularia.