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Decima, M, Landry MR, Stukel MR, Lopez-Lopez L, Krause JW.  2016.  Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web. Journal of Plankton Research. 38:317-330.   10.1093/plankt/fbv091   AbstractWebsite

We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (<2-mu m cells) with especially high concentrations of Synechococcus spp., we found high mesozooplankton biomass (similar to 5 g dry weight m(-2)) and grazing impact (12-50% integrated water column chlorophyll a), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web.

Decima, M, Landry MR, Rykaczewski RR.  2011.  Broad scale patterns in mesozooplankton biomass and grazing in the eastern equatorial Pacific. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 58:387-399.   10.1016/j.dsr2.2010.08.006   AbstractWebsite

We investigated biomass distributions and grazing rates of mesozooplankton in the eastern equatorial Pacific between 110 degrees-140 degrees W and 4 degrees S-4 degrees N during cruises in December 2004 (EB04) and September 2005 (EB05). Median (+/- SE) euphotic zone estimates of zooplankton biomass, collected with a 200-mu m mesh net, varied from 2.27 +/- 0.24 g dry weight m(-2) during EB04 to 3.13 +/- 0.22 g dry weight m(-2) for EB05 (however, when stations from overlapping regions were compared, no significant differences were found between years). Trends in gut fluorescence estimates of mesozooplankton grazing followed biomass, with significantly higher median rate estimates during EB05 (3.39 +/- 0.32 mg pigment m(-2) d(-1)) than during EB04 (2.31 +/- 0.34 mg pigment m(-2) d(-1)). Spatial gradients in mesozooplankton biomass and grazing on meridional transects sampled at 110 degrees W in 2004 and 140 degrees W in 2005 could be interpreted as either in situ growth/grazing responses or downstream advective flows relative to spatial patterns in phytoplankton. The present zooplankton biomass estimates for the equatorial Pacific are 80-90% higher than those from similar measurements made by the US Joint Global Ocean Flux Studies EqPac Program in 1992. Our grazing rates similarly exceed EqPac estimates by a factor of 2 or 3, in absolute terms and as percent of phytoplankton biomass consumed daily (11% - EB04; 14% - EB05). Although the equatorial region has not been regularly sampled between EqPac and the present study, both the magnitude and the direction of the observed changes are consistent with the documented decadal increase in mesozooplankton biomass in the adjacent North Pacific Subtropical Gyre based on monthly sampling at Stn. ALOHA, as well as an increase in the strength of the trade winds. These results may be indicative of a general shift up in productivity or community size structure and role of mesozooplankton in the open-ocean tropical/subtropical Pacific, and they provide important time points for validating the performance of ecosystem models of the region. (C) 2010 Elsevier Ltd. All rights reserved.

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.

Landry, MR, Lorenzen CJ, Peterson WK.  1994.  Mesozooplankton grazing in the Southern California Bight .II. Grazing impact and particulate flux. Marine Ecology-Progress Series. 115:73-85.   10.3354/meps115073   AbstractWebsite

Mesozooplankton grazing on phytoplankton, as inferred from gut pigment contents and gut evacuation rates, was studied in relation to primary production and particulate export flux on 6 cruises in the Santa Monica Basin, California, USA. Gut evacuation rates did not vary significantly among different taxa or size classes examined and were consistent with extrapolations of published temperature relationships. Shipboard incubations with cultured phytoplankton and net-collected zooplankton indicated a seasonal difference in the extent to which gut passage converts chlorophyll to non-fluorescent by-products. In autumn experiments, only about 5% of ingested chlorophyll could not be recovered as phaeopigment. In winter-spring experiments, approximately 70% of ingested chlorophyll (chl) was destroyed. In contrast, other indices of pigment destruction, the ingestion rates of a dominant copepod species and the ratio of water-column phaeopigment:silica fluxes, did not reveal a significant gut passage effect during winter-spring cruises. Mesozooplankton community grazing impact varied from 1.7 to 7.3 mg chi m(-2) d(-1), with higher grazing during the winter-spring period (mean = 5.8 mg chi m(-2) d(-1)) as compared to the autumn (mean = 2.3 mg chi m(-2) d(-1)). On average, mesozooplankton grazing accounted for a loss of 11.7% of chlorophyll standing stock d(-1) with a 6 cruise range of 6 to 18% d(-1). Mesozooplankton grazing on phytoplankton accounted for 29 to 44% (mean = 39%) of measured primary production for the winter-spring cruises, but only 16 to 24% (mean = 19%) of production in the autumn. From measured phaeopigment fluxes into sediment traps below the euphotic zone, only 27.5% (range 23 to 32%) of this grazing on phytoplankton could be accounted for as export flux. Thus, in terms of contribution to particulate flux or remineralization, most mesozooplankton grazing in the Santa Monica Basin was functionally equivalent to that of microzooplankton. Direct grazing on phytoplankton contributed 15 to 38% of carbon flux into sediment traps during winter-spring and 8 to 13% during autumn. Nonetheless, if feeding on nonpigmented prey is considered from the available information on carbon:phaeopigment ratios of fresh fecal pellets, over 70% of the carbon flux to traps could have a mesozooplankton grazing origin.