role of Synechococcus in vertical flux in the Costa Rica upwelling dome

• Published in: Progress in oceanography 2013-05, Vol.112, p.49-59
• Main Authors: Stukel, Michael R, Décima, Moira, Selph, Karen E, Taniguchi, Darcy A.A, Landry, Michael R
• Format: Article
• Language: English
• Subjects: carbon; cell aggregates; chlorophyll; digestive system; ecosystems; euphotic zone; feces; flow cytometry; grazing; microscopy; phycoerythrin; phytoplankton; pigments; predation; primary productivity; Protozoa; sediments; Synechococcus
• ISSN: 0079-6611; 1873-4472
• DOI: 10.1016/j.pocean.2013.04.003

Despite evidence that picophytoplankton contribute to export from marine pelagic ecosystems to some extent, few field studies have experimentally evaluated the quantitative importance of that flux or specifically assessed the relative strengths of alternate ecological pathways in transporting picophytoplankton carbon to depth. In experimental studies in the Costa Rica Dome (CRD), we used a combination of methods – flow cytometry (FCM), microscopy, pigments, dilution assays, mesozooplanton gut contents and sediment traps – to follow production, grazing and export fates of the dominant picophytoplankter, Synechococcus spp. (Syn), relative to the total phytoplankton community. Syn accounted for an average of 25% (range 9–50%) of total phytoplankton production during four 4-day drifter experiments at CRD sites. During the same experiments, sediment trap deployments at the base of the euphotic zone measured total organic carbon export ranging from 50 to 72mgCm⁻²d⁻¹. Flow cytometry measurements of the trap samples showed that only 0.11% of this carbon was recognizable as ungrazed sinking Syn. Phycoerythrin (PE) measurements on the same samples, which we attributed mostly to transport of intact cells in mesozooplankton fecal pellets, gave export contributions of unassimilated Syn eight-times higher than ungrazed sinking cells, though still