Measurement of photosynthetic parameters in benthic organisms in situ using a SCUBA-based fast repetition rate fluorometer

Benthic photoautotrophic organisms significantly contribute to the producti vity of shallow tropical coastal ecosystems. However, measurements of photo synthetic light use and dissipation in benthic organisms are complicated by taxonomic diversity, spatial heterogeneity, natural variability in local n utrient, irradiance, and temperature regimes, as well as destructive sampli ng protocols. To help overcome these problems, we developed a SCUBA-based f ast repetition rate (FRR) fluorometer for measurements of variable chloroph yll fluorescence in corals, sea grasses, macroalgae, and algal turfs. Photo synthetic light use and electron transport can be readily calculated from v ariable fluorescence kinetics. Using the SCUBA-based FRR fluorometer, chang es in photosynthetic processes can be measured nondestructively in situ wit h high spatial and temporal resolution. Here we describe the instrument des ign and characteristics and present representative field results.