PAM chlorophyll fluorometry: a new in situ technique for stress assessmentin scleractinian corals, used to examine the effects of cyanide from cyanide fishing

Sodium cyanide is being used on reefs in the Asia-Pacific region to capture live fish for the aquarium industry, and to supply a rapidly growing, rest aurant-based demand, The effects of cyanide on reef biota have not been ful ly explored. To investigate its effect on hard corals, we exposed small bra nch lips of Stylophora pistillata and Acropora aspera to cyanide concentrat ions estimated to occur during cyanide fishing. Pulse amplitude modulation (PAM) chlorophyll fluorescence techniques were used to examine photoinhibit ion and photosynthetic electron transport in the symbiotic algae (zooxanthe llae) in the tissues of the corals, These measurements were made in situ an d in real time using a recently developed submersible PAM fluorometer. In S . pistillata. exposure to cyanide resulted in an almost complete cessation in photosynthetic electron transport rate. Both species displayed marked de creases in the ratio of variable fluorescence (F-v) to maximal fluorescence (F-m) (dark-adapted F-v/F-m), following exposure to cyanide, signifying a decrease in photochemical efficiency. Dark-adapted F-v/F-m recovered to nor mal levels in similar to 6 d, although intense tissue discolouration, a phe nomenon well-recognised as coral 'bleaching' was observed during this perio d, Bleaching was caused by loss of zooxanthellae from the coral tissues, a well-recognised sub-lethal stress response of corals. Using the technique o f chlorophyll fluorescence quenching analysis, corals exposed to cyanide di d not show light activation of Calvin cycle enzymes and developed high leve ls of non-photochemical quenching (q(N)), signifying the photoprotective di ssipation of excess light as heat, These features are symptomatic of the kn own properties of cyanide as an inhibitor of enzymes of the Calvin cycle. T he results of this in situ study show that an impairment of zooxanthellar p hotosynthesis is; the site of cyanide-mediated toxicity, and is the cue tha t causes corals to release their symbiotic zooxanthellac following cyanide exposure. This study demonstrates the efficacy of PBM fluorometry as a new tool for in situ stress assessment in zooxanthellate scleractinian corals. (C) 1999 Elsevier Science Ltd. All rights reserved.