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

Benthic photoautotrophic organisms significantly contribute to the productivity of shallow tropical coastal ecosystems. However, measurements of photosynthetic light use and dissipation in benthic organisms are complicated by taxonomic diversity, spatial heterogeneity, natural variability in local nutrient, irradiance, and temperature regimes, as well as destructive sampling protocols. To help overcome these problems, we developed a SCUBA-based fast repetition rate (FRR) fluorometer for measurements of variable chlorophyll fluorescence in corals, sea grasses, macroalgae, and algal turfs. Photosynthetic light use and electron transport can be readily calculated from variable fluorescence kinetics. Using the SCUBA-based FRR fluorometer, changes in photosynthetic processes can be measured nondestructively in situ with high spatial and temporal resolution. Here we describe the instrument design and characteristics and present representative field results.