Fast repetition rate (FRR) fluorometry: variability of chlorophyll a fluorescence yields in colonies of the corals, Montastraea faveolata (w.) and Diploria labyrinthiformes (h.) recovering from bleaching

Recently, an underwater version of a fast repetition rate fluorometer (FRRF ) was developed for the non-destructive study of fluorescence yields in ben thic photoautotrophs. We used an FRRF to study bleached colonies of the cor als, Montastraea faveolata and Diploria labyrinthiformes at sites surroundi ng Lee Stocking Island, Exuma, Bahamas, to assess their recovery from bleac hing (similar to 1 year after the initial bleaching event) induced by eleva ted temperatures. The steady state quantum yields of chlorophyll a fluoresc ence (Delta F'/F-m') from photosystem II (PSII) within coral colonies were separated into three categories representing visibly distinct degrees of bl eaching ranging from no bleaching to completely bleached areas. Differences in Delta F'/F-m' were significantly different from bleached to unbleached regions within colonies. Dark, unbleached regions within colonies exhibited significantly higher Delta F'/F'(m) values (0.438+/-0.019; mean+/-S.D.) wh en compared to lighter regions, and occupied a majority of the colonies' su rface area (46-73%). Bleached regions exhibited significantly lower Delta F '/F-m' (0.337+/-0.014;) and covered only 7-25% of the colonies' surface are a. The observations from this study suggest that zooxanthellae in bleached regions of a colony exhibit reduced photosynthetic activity as long as one year after a bleaching event and that in situ fluorescence techniques such as FRRF art: an effective means of studying coral responses and recovery fr om natural or anthropogenic stress in a non-destructive manner. (C) 2000 El sevier Science B.V. All rights reserved.