Year-round variations in reserve lipid molecular species of the Indo-Pacific corals Sinularia flexibilis and Millepora platyphylla.

Lipid molecular species profiles of marine invertebrates still remain very poorly understood. We have studied year-round variations in the levels of chlorophylls and reserve lipid molecular species such as triacylglycerols (TG), and monoalkyldiacylglycerol (MADAG) in octocoral Sinularia flexibilis and the hydrocoral Millepora platyphylla. Our results show that M. platyphylla and S. flexibilis display differences in the pattern of year-round variations in reserve lipids. Only in M. platyphylla, total reserve lipids correlated with seawater temperature, which may be associated with hydrocoral's predation on plankton. A decrease in total lipids leads to an increase in chlorophyll levels, which indicates transition to autotrophic nutrition mode. Differences between corals also may be associated with species of hosted symbiotic dinoflagellates that can be a source of fatty acids (FAs) for the biosynthesis of TG and MADAG by the coral host. This may be an explanation for the annual variations in TG molecular species with 22:6 PUFA in M. platyphylla, and TG molecular species with saturated, mono-, and dienoic FAs in S. flexibilis. Based on S. flexibilis as an example, we have shown that MADAGs are suggested to have several molecular pools, of which one may be related to the molecular profile of structural phospholipids with the same FAs. Year-round studies of lipidome can help understand the range and possible causes of seasonal biochemical variations in corals and may be useful for future analysis of trophic and symbiont–host interactions in cnidarians. [ABSTRACT FROM AUTHOR]