Seasonal variation in the lipidome of two species of Millepora hydrocorals from Vietnam coastal waters (the South China Sea)

In shallow tropical seas, hydrocoral colonies are locally abundant and important reef-framework builders. Hydrocorals are rich in lipids, which play an essential role in their physiology, but no data on seasonal variations in lipids of hydrocorals are available to date. In the present study, the profiles of total lipids, fatty acids (FA), storage and structural lipids classes, and molecular species of structural lipids in symbiotic dinoflagellates and the host of the hydrocorals Millepora dichotoma and M. platyphylla were analyzed each month throughout the year. In both hydrocoral species, the twofold increase in total lipids in the summer coincided with the water temperature rise and was caused primarily by the considerable accumulation of storage lipids with insignificant variations in structural lipids. The FA markers confirmed the year-round hydrocorals’ predation on zooplankton and indicated that M. dichotoma can consume more diatoms than M. platyphylla during October–January. The polar lipidomes of the two Millepora species were similar. The remodeling of alkyl and sphingosine groups in three structural lipid classes rather than unsaturation degree of their FA groups may be considered as a seasonal adaptive response of host biomembranes in Millepora . The symbiotic dinoflagellates of the hydrocorals kept the galactolipid ratio stable throughout the year but significantly increased the levels of sulfoquinovosyldiacylglycerol and betaine lipid in winter. The FA markers of the symbionts correlated negatively with galactolipids, thus, indicating a higher transfer of the symbiotic FA to the host in winter. Throughout the year, symbionts controlled their lipid class composition, but their lipid molecular species composition varied in a random manner. The considerable amounts of digalactosyldiacylglycerols with C 20–22 polyunsaturated FA distinguished M. platyphylla from M. dichotoma and suggested that different hydrocorals contain different symbiont species. Data on seasonal variations of the lipidomes provide new background information for future studies of ecology, physiology, and biochemistry of hydrocorals.