Temporal variation in lipid, protein and carbohydrate content in the Red Sea soft coral Heteroxenia fuscescens

Heteroxenia fuscescens is a common zooxanthellate soft coral on the shallow reefs of the Gulf of Eilat, northern Red Sea. Its main nutritional sources are the uptake of dissolved organic material (DOM) and carbon fixation by its symbiotic algae (zooxanthellae). Recent studies have indicated that although colonies of H. fuscescens release planulae all year round, their fecundity was subject to seasonal changes. In this study the monthly per cent of ash, lipid, protein and carbohydrate in the coral tissue over a three year period was determined. It was found that the tissues of colonies of H. fuscescens contained a monthly per cent mean of 8.8 +/- 4 ash (without sclerites), 11 +/- 3.5 lipid, 19.2 +/- 6.4 protein, and 0.6 +/- 0.01 carbohydrate (N=36). This study is the first to present such values based on long term investigation of the biochemical profile of a coral, thus enabling an examination of temporal variability in biochemical composition among seasons and successive years. The results indicated seasonal fluctuations in lipid and protein content, while variation in the biochemical composition among years was expressed only in the protein content. The mean energetic content of H. fuscescens was relatively high at 23.3 +/- 1.2 kJ g(-1) dry weight (DW). A significant difference in the energetic content of H. fuscescens was found among seasons. It is suggested that the increase in nutrient levels following the annual mixing event at the Gulf of Eilat and the raised light levels led to high energetic content during summer, which may reflect the increase in the number of embryos and developing planulae in H. fuscescens colonies. Furthermore, it is suggested that in the Gulf of Eilat seasonal fluctuations in the abiotic features of the water may have an impact on the biochemical composition and energetic content of the studied species.