López-Rosado, Ramón

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    Photosynthetic efficiency of phototrophic plankton and bio-optical variability as influenced by mesoscale processes in the eastern Caribbean basin
    (2008-12) López-Rosado, Ramón; López-Díaz, José M.; College of Arts and Sciences - Sciences; Armstrong, Roy A.; Corredor, Jorge E.; Gilbes, Fernando; Morell, Julio; Aponte, Nilda E.; Department of Marine Sciences; Lorenzo, Edgardo
    This study comprises an analysis of photosynthetic potential of phototrophic plankton in eastern Caribbean Sea near-surface waters as influenced by the action of mesoscale processes. The massive freshwater plume from the Orinoco River and mesoscale cyclonic and anti-cyclonic eddies are two common types of features in the Eastern Caribbean Sea. The physiological state of phototrophic plankton was addressed by measuring its photosynthetic efficiency using a fast repetition rate fluorometer (FRRF) throughout the region. The Fv/Fm parameter measures the changes in phototrophic plankton physiology by a rapid, noninvasive assessment of in vivo fluorescence signatures. The FRRF provided fast and accurate quantification of changes in productivity in response to environmental forcing at the ecologically relevant scales of mesoscale processes. Enhanced biological activity has been associated with these features which stimulate the input of limiting nutrients into the euphotic zone. FRRF measurements showed that photosynthetic efficiency varied vertically in areas of upward pycnocline displacement of isohalines and thermal structures suggesting that nutrient upwelling is responsible for the higher photosynthetic efficiency observed at surface. The influence of the Orinoco River plume on the photosynthetic potential demonstrated increased Fv/Fm close to the surface, decreasing with depth, suggesting a relationship with river originated material. Independent measurements of photosynthetically mediated 14C uptake produced a strong linear relationship (r = 0.91) with the FRRF-based primary productivity estimates for data collected throughout the region. These estimates covaried with satellite-based estimates of primary production through the environmental gradients created by the Orinoco River plume. Correlation analysis was used to describe the relationship between phototrophic plankton physiological state (Fv/Fm) and independent measurements of bio-optical variables.The beam attenuation to chlorophyll ratio (cp *) demonstrated inverse correlation with Fv/Fm as a result of the baroclinic instabilities created by eddies. The phytoplankton specific absorption coefficient (aph) showed reduced absorption in the region of 442 nm apparently in response to increased package effect for waters under the influence of the river plume. Variations in the aph slope were associated to a decrease in the quantum yield for carbon fixation in samples from oceanic waters far from the direct influence of the Orinoco River plume.