Study on the year-round fluctuation of total lipid content and lipid classes composition in soft coral \(\textit{Sinularia flexibilis}\) from Nha Trang, Khanh Hoa coastal

The samples of soft coral Sinularia flexibilis were collected from January to December in one year from Nha Trang, Khanh Hoa coastal. Initial assessment the month-by-month fluctuation of total lipid content and lipid classes composition in this species was conducted. Total lipid content reached the highest value during March to May, lower in the period of June-September and bottomed in October and November. There was a significant decrease in this content between May and June; September and October; the content increase from February to March but not stable during October to February. The lipid classes composition of Sinularia flexibilis includes polar lipids (PL), sterols (ST); triacylglycerol (TAG), monoalkyldiacyl-glycerol (MADAG), wax (W) and free fatty acids (FFA). The concentration of PL in summer (April-August) was lower than that in winter (September-February), this content increased significantly during November-December meanwhile it was observed to decrease in April-May, December-January. The content of ST increased from October to March and declined from April to September. The remain classes including W, MADAG, TAG tend to increase in the summer period and decline in the other months. The fluctuation of lipid classes composition throughout the year is closely related to the presence of zooxanthellae microalgae in corals at different times of the year and is directly influenced by environmental conditions, especially sea water temperature. In addition, the effect of maturation and reproduction of this coral with the increase or release of reproductive materials also observed.