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Landry, MR, Ohman MD, Goericke R, Stukel MR, Tsyrklevich K.  2009.  Lagrangian studies of phytoplankton growth and grazing relationships in a coastal upwelling ecosystem off Southern California. Progress in Oceanography. 83:208-216.   10.1016/j.pocean.2009.07.026   AbstractWebsite

Experimental studies of phytoplankton growth and grazing processes were conducted in the coastal upwelling system off Point Conception, California to test the hypothesis that phytoplankton growth and grazing losses determine, to first order, the local dynamics of phytoplankton in the upwelling circulation. Eight experiments of 3-5 days each were conducted over the course of two cruises in May-June 2006 and April 2007 following the trajectories of satellite-tracked drifters. Rates of phytoplankton growth and microzooplankton grazing were determined by daily in situ dilution incubations at 8 depths spanning the euphotic zone. Mesozooplankton grazing was assessed by gut fluorescence analysis of animals collected from net tows through the euphotic zone. We compared directly the net rates of change observed for the ambient phytoplankton community to the net growth rates predicted from experimental determinations of each process rate. The resulting relationship accounted for 91% of the variability observed, providing strong support for the growth-grazing hypothesis. In addition, grazing by mesozooplankton was unexpectedly high and variable, driving a substantial positive to negative shift in phytoplankton net rate of change between years despite comparable environmental conditions and similar high growth rates and suggesting strong top-down control potential. The demonstrated agreement between net ambient and experimental community changes is an important point of validation for using field data to parameterize models. Data sets of this type may provide an important source of new information and rate constraints for developing better coupled biological-physical models of upwelling system dynamics. (C) 2009 Elsevier Ltd. All rights reserved.

Chekalyuk, AM, Landry MR, Goericke R, Taylor AG, Hafez MA.  2012.  Laser fluorescence analysis of phytoplankton across a frontal zone in the California Current ecosystem. Journal of Plankton Research. 34:761-777.   10.1093/plankt/fbs034   AbstractWebsite

Spatial variability of chlorophyll, phycobiliproteins, chromophoric dissolved organic matter and variable fluorescence (F-v/F-m) was analyzed across a deep-water density front in the Southern California Current Ecosystem using an Advanced Laser Fluorometer (ALF) calibrated to assess chlorophyll concentration (C-chl), total autotrophic carbon (AC) and Synechococcus carbon biomass (SYN). Three distinct autotrophic assemblages were identified. Fluorescence was found to be three to four times higher in cooler mesotrophic waters north of the front than in warm oligotrophic waters to the south. Northern waters were distinguished by a shallow pigment maximum dominated by a blue-water type of Synechococcus and by the presence of green-water Synechococcus and cryptophytes; only blue-water Synechococcus were detected at lower concentration south of the front. The highest C-chl and AC values, accompanied by elevated F-v/F-m and chlorophyll fluorescence per unit of C-chl, and minimal Synechococcus abundance, were found directly at the front in a 2040 m deep layer dominated by diatoms. The covariation of F-v/F-m with nitrate concentration in this layer, along with the structural changes in the phytoplankton community, suggest that it had been generated by in situ processes rather than advection. Strong structural responses to the local hydrography were also revealed by high-frequency underway ALF surface sampling, which detected an abrupt transition from low to high SYN on the northern side of a sharp salinity gradient at the front. Synechococcus-specific phycoerythrin fluorescence (F-PE12) and SYN were highly correlated in surface waters (R-2 0.95), while F-PE12:SYN gradually increased with depth. Strong relationships were found for chlorophyll fluorescence versus C-chl (R-2 0.95) and AC (R-2 0.79).

Miller, CB, Denman KL, Gargett AE, Mackas DL, Wheeler PA, Booth BC, Frost BW, Landry MR, Lewin J, Lorenzen CJ, Perry MJ, Dagg MJ, Welschmeyer N.  1985.  Lower trophic level production dynamics in the oceanic Subarctic Pacific. Japan-United States of America Seminar on the Biology of Micronekton of the Subarctic Pacific. 26( Nemoto T, Pearcy WG, Miller CB, Eds.).:1-26., Honolulu, HI (USA) Abstract

Upper waters of the subarctic Pacific are the principal example of a balanced pelagic ecosystem in which phytoplankton growth is continuously matched by grazing so that blooms do not occur. New data suggest that microzooplankton (less than 100 mu m) provide much of the grazing required. Large, filter-feeding calanid copepods with life histories peculiar to this region can no longer be considered the only agents sustaining balance. A phytoplankton-pigment budget approach to grazing implied that "microzooplankton" contributed more grazing than "macrozooplankton".