Fluorescence signatures of persistent photosystem damage in the staghorn coral Acropora cf. pulchra (Anthozoa: Scleractinia) during bleaching and recovery

Abstract

ABSTRACT Staghorn corals represent dominant reef-builders in lagoons and back reefs in Guam. These habitats experience peak seawater temperatures close to 36°C during the hottest months of the year which causes increasingly frequent bleaching episodes that have led to major staghorn coral declines. To study the photo-physiological response of staghorn corals to bleaching conditions, pulse amplitude modulated (PAM) fluorometry was used to record signatures of chlorophyll fluorescence in Acropora cf. pulchra. Fragments of A. cf. pulchra were subjected to a week-long heat treatment some 2–3°C above average ambient seawater temperatures of 30°C; a four-week long recovery period at ambient temperatures followed treatment. While heat-treated coral fragments exposed to full sun responded with immediate and lasting declines in photosynthetic efficiency, shading of coral fragments largely mitigated the effects of elevated seawater temperatures. Of particular concern to reef management efforts is the finding that the strongest effects of heat stress were observed during the recovery period following the initial heat stress. Indeed, it took three times as long as the initial stress event lasted for photosynthesis to return to baseline levels. This lengthy recovery period appears to be driven by photodamage, likely requiring time-consuming protein synthesis-dependent repair of damaged photosystems and replacement of damaged zooxanthellae. These results highlight the importance of developing and implementing coral bleaching intervention efforts well beyond the end of bleaching conditions to facilitate recovery of affected reefs.