Three procedures for the extraction of coral lipids were compared and a rapid and effective method for future use is suggested. This method was used to measure the lipid content of the branching coral Porites porites (Pallas) and the massive corals Montastrea annularis (Ellis and Solander) and Siderastrea siderea (Ellis and Solander) during July and August 1991. P. porites and M. annularis were sampled on two fringing reefs, each characterised by different water quality affecting light transmission, and at depths of down to 30 m on a barrier reef on the west coast of the island. M. annularis contained, on average, 29 % of dry weight as lipid, and there were no significant differences in lipid levels between corals sampled on either fringing reef at 3 and 6 m, or between fringing reefs and the barrier reef at 13, 20 or 30 m depth. Five samples were also taken from a single massive colony of S. siderea at 3 m on a fringing reef and at 13, 20 and 30 m depth on the barrier reef. Values for lipid ranged from 26 to 35% of dry tissue weight. P. porites from 3 and 6 m depth on both fringing reefs contained the same amount of lipid (,~ 11% of dry tissue weight). However, at 13 m depth on the barrier reef this coral contained significantly less lipid (8.5 % of dry tissue weight). This difference may be attributable to a higher nutritional intake by P. porites on the fringing reefs. etal. 1980reefs. etal. , Crossland 1987)). Corals contain large amounts of lipid, and values of between 30 and 46% of dry tissue weight have reported (Bergmann et al. 1956, Patton et al. 1977, Stimson 1987).
Corals which live at low light intensities may not have the potential to be autotrophic with respect to carbon, and must therefore obtain some carbon heterotrophically (Davies 1977, Muscatine et al. 1984). Davies (1991) suggested that on overcast days, shallow-water corals ]nay not be autotrophic and would have to metabolise stored lipid. Experiments in which corals were artificially shaded showed that those maintained at lower light levels contained less lipid (Stimson 1987), andHarland et al. (1992) demonstrated that the levels of storage and total lipids of a symbiotic sea anemone were proportional to light intensity and also depended upon whether the anemones were fed or starved.
This study had two objectives. Firstly, to evaluate and compare three different lipid extraction procedures to provide a simple method for use in field laboratories. Secondly, to examine the effect of the reduced levels of light encountered with increasing water depth on the lipid levels of three species of reef coral. Samples were analysed from fringing and barrier reefs in Barbados at depths of between 3 and 30 m. In addition, corals were analysed from the same depths (3 and 6 m) on two fringing reefs, one of which is characterised by high levels of suspended particulates, affecting light transmission.