Response of corals to changes in solar radiation and temperature

Abstract

The measurement of chlorophyll a fluorescence using active techniques is fast becoming the preferred, non-destructive, in situ method to assess PSII function in benthic marine photoautotrophs under a variety of environmental conditions. Chlorophyll a fluorescence has been an important tool of photobiologists starting with the discovery of fluorescence induction and leading to fluorescence measurements using the herbicide DCMU that then became an important tool for photobiologists. Recently, instruments have been developed that measure chlorophyll fluorescence yields of PSII using multiple photochemical turnover (pulse amplitude modulated [PAM]), and single photochemical turnover protocols (pump and probe or fast repetition rate [FRR]) in the laboratory and in the field. These instruments also allow detailed quenching analyses to be performed on photoautotrophs under a variety of environmental conditions to understand the dynamics between photochemical and non-photochemical quenching. Applications for these instruments include studies on diel changes in quantum yields of PSII, the effects of ultraviolet radiation (290-400 nm) on PSII, and temperature effects on PSII leading to bleaching in corals. The endosymbiotic dinoflagellates of corals (=zooxanthellae) may be especially sensitive to these perturbations in hospite because of sink limitations (e.g., either nitrogen or inorganic carbon) and a hyperoxic environment which can lead to oxidative stress and PSII dysfunction.