Energy reserves and metabolism as indicators of coral recovery from bleaching

TLDR

Bleached corals depend on energy reserves and heterotrophy to survive and recover when zooxanthellae or chlorophyll a levels are reduced. The study aimed to investigate how energy reserves and metabolism change during long‑term recovery of Porites compressa and Montipora capitata after experimental bleaching. Researchers experimentally bleached corals for one month, then monitored recovery on the reef at 0, 1.5, 4, and 8 months, comparing treated corals to ambient‑temperature controls. At baseline, bleached corals had lower chlorophyll, energy reserves, and photosynthesis than controls; during recovery, Montipora capitata replenished energy reserves within 1.5 months independent of photosynthetic recovery, while Porites compressa required 8 months to restore reserves and biomass, indicating that M.

Abstract

With reduced zooxanthellae, chlorophyll a (Chl a ), or both, concentrations, bleached corals rely on some combination of energy reserves (i.e., lipid, carbohydrate, protein) and heterotrophy to survive and recover. To understand the dynamics of energy reserves and metabolism during long‐term recovery, Porites compressa and Montipora capitata corals were experimentally bleached in outdoor tanks for 1 month (treatment corals). Additional corals were maintained in separate tanks at ambient temperatures (control corals). Recovery occurred on the reef for 0, 1.5, 4, or 8 months. At 0 months all treatment corals were white in color, with lower Chl a , lipid, carbohydrate, protein, tissue biomass, and photosynthesis than control corals. During recovery, P. compressa replenished energy reserves and tissue biomass at 8 mo, long after photosynthesis and Chl a had recovered at 1.5 and 4 months, respectively. M. capitata replenished energy reserves at 1.5 months, despite decreased Chl a and photosynthesis levels. P. compressa depends on photosynthetically fixed carbon for recovery from bleaching, whereas M. capitata does not. Overall, M. capitata had a faster recovery rate than P. compressa for all measured variables except Chl a concentration. With intensifying bleaching, coral diversity on future reefs may favor species with faster recovery rates.