Location, Quantity and Rate of Change in Quantity of Lipids in Tissue of Hawaiian Hermatypic Corals

The location, quantity, and rate of change of quantity of lipids were assessed in polyps of six of the major species of Hawaiian reef corals in order to understand how corals use the large quantities of lipid they possess. Lipid occurs in the mesoglea of the column and base of some polyps, in the endoderm of some polyps, in the coelenteron of planulae, in the endoderm of polyps adjacent to eggs, in eggs, and in "fat bodies" that develop from the stomodaeum and which eventually appear loose in the coelenteron of polyps of Pocillopora spp. Lipid, as a percentage of dry tissue weight, constitutes between 30 and 40% of tissue in Hawaiian corals collected in shallow water. Inter-species comparisons indicate that there are significant differences in the quantity of lipid in the tissues of the five species tested. Lipid content is high in both planulating and spawning species. The quantity of lipid in the Y type of Pocillopora damicornis (Richmond and Jokiel, 1984) varies cyclically, possibly with a period of 1 lunar month, while no cycle is apparent in the lipid content of the less fecund B type. Decreasing lipid concentrations coincide with the monthly occurrence of planulation in the Y type colonies, but planulation reduces lipid reserves by only ∼30% in individual branch tips. Rapid increase or decrease in light level results in a long term increase or decline respectively in lipid levels over a period of 1–2 weeks. Colonies kept at experimentally reduced light levels had both lower lipid levels and lower rates of vertical branch growth. The large quantity of lipid reportedly discharged by corals, the large amounts of fat stored in coral polyps, and the production of fat bodies which may be released by polyps give support to the contention of Crossland et al. (1980a) that zooxanthellae living in shallow water corals supply host polyps with an excess of energy-rich lipid. Evidence presented here suggests that the large amount of lipid found in shallow water corals constitutes an energy reserve.