Lipid class composition of bleached and recovering Porites compressa Dana, 1846 and Montipora capitata Dana, 1846 corals from Hawaii

Corals rely on stored reserves, especially lipids, to survive bleaching events. Lipid class composition reveals the lipid source, and provides evidence of metabolic changes (i.e., photoautotrophic or heterotrophic) during bleaching and recovery. Porites compressa Dana, 1846 and Montipora capitata Dana, 1846 corals were experimentally bleached in outdoor tanks with seawater temperature elevated to 30 °C (treatment corals). Additional control fragments were maintained in separate tanks at ambient temperatures (27 °C). After one month, all fragments were returned to the reef for 0, 1.5, 4, or 8 months. Lipid class composition was analyzed by Iatroscan (thin layer chromatography-flame ionization detection). In treatment P. compressa, triacylglycerol (TG) decreased at 0 and 1.5 months, phospholipid (PL) also decreased at 1.5 months, and both remained lower relative to controls along with wax esters (WE) after 8 months. Neither treatment nor control P. compressa had any detectable monoacylglycerol (MG) or diacylglycerol (DG). Overall, P. compressa first consumed available storage, then structural lipids, and all lipid classes remained low at the end of the study. In treatment M. capitata, TG and PL decreased, while MG increased relative to controls at 0 months. At 4 months, free fatty acid (FFA), sterol (ST), and PL in treatment M. capitata were two to ten times higher than controls. Treatment and control lipid class composition were not different from each other at 8 months. In contrast to P. compressa, M. capitata consumed some lipid classes and augmented others, probably due to sequential metabolism of storage lipids and increased heterotrophy. Overall, lipid class assimilation was more rapid in treatment M. capitata corals that switch between heterotrophy and photoautotrophy, than in treatment P. compressa corals that rely mostly on photoautotrophy.