Food sources of suspension-feeding bivalves, Isognomon sp. in the Setiu Weland, Terengganu as assessed by fatty acid biomarker

Abstract

The bivalvia Isognomon sp. and Suspended Particulate Material (SPM) were collected in the Lagoon of Setiu Wetland, Terengganu in August, October and December 2007. The fatty acid composition in the tissue of Isognomon sp. were compared with those in its' feces and in SPM in order to assess the oysters' food sources. The mean concentration of total lipid in tissue shows the differences among months. The differences in the amount of total lipid in the tissue of Isognomon sp. in each month could be caused by physiological condition and food supply of this oyster species. Six lipid components comprise of phospholipids, sterols, free fatty acids, triglycerols, fatty acids and waxes were obtained in all samples. The fatty acids in groups of polyunsaturated fatty acids (PUF A), saturated fatty acid (SAFA), monounsaturated fatty acid (MUF A) and branching fatty acids (BrF A) were recorded in all component in all sampling month. The fatty acids that contributed most were in the class of PUF A. A total of 42 fatty acids were recorded in the tissue of Isognomon sp. Microlagae markers were higher in the tissue, SPM and feces of the Isognomon sp. in all sampling month except for December. Analysis on gut content of the Isognomon sp. also shows the high contribution of microalgae in the stomach of the animals. In December, the mangrove detritus markers show the significantly higher contribution in feces and SPM component. The higher contribution of mangrove detritus markers might be caused by high mangrove litter production due to the heavy rainfall in December. To conclude, the result shows that microalgae form the main component of these bivalves diet. The contribution of other markers such as mangrove detritus, bacteria, copepod and green macroalgae markers shows that Isognomon sp. also consumes other sources such as mangrove detritus, bacteria, copepod and green macroalgae as their food sources in all sampling month.