Bleached Porites compressa and Montipora capitata corals catabolize δ13C-enriched lipids

Corals rely on stored energy reserves (i.e., lipids, carbohydrates, and protein) to survive bleaching events. To better understand the physiological implications of coral bleaching on lipid catabolism and/or synthesis, we measured the delta C-13 of coral total lipids (delta C-13(TL)) in experimentally bleached (treatment) and non-bleached (control) Porites compressa and Montipora capitata corals immediately after bleaching and after 1.5 and 4 months of recovery on the reef. Overall delta C-13(TL) values in treatment corals were significantly lower than in control corals because of a 1.9 and 3.4aEuro degrees decrease in delta C-13(TL) immediately after bleaching in P. compressa and M. capitata, respectively. The decrease in delta C-13(TL) coincided with decreases in total lipid concentration, indicating that corals catabolized delta C-13-enriched lipids. Since storage lipids are primarily depleted during bleaching, we hypothesize that they are isotopically enriched relative to other lipid classes. This work further helps clarify our understanding of changes to coral metabolism and biogeochemistry when bleached and helps elucidate how lipid classes may influence recovery from bleaching and ultimately coral survival.