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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.

Huntley, ME, Lopez MDG, Zhou M, Landry MR.  2006.  Seasonal dynamics and ecosystem impact of mesozooplankton at station ALOHA based on optical plankton counter measurements. Journal of Geophysical Research-Oceans. 111   10.1029/2005jc002892   AbstractWebsite

[1] Abundances of mesozooplankton-sized particles were measured at 45-m depth at station ALOHA (22.75 degrees N, 158 degrees W) during 18 cruises from February 1995 through December 1996 with an optical plankton counter (OPC). Mesozooplankton were also sampled with oblique net tows to 155 m depth. Vertical OPC profiles showed uniform total abundance in the upper mixed layer, usually > 45 m. OPC and net data agreed with respect to total abundance, size composition, abundance of individual size classes, and seasonal cycle of abundance. We found no evidence for significant contributions to OPC particle counts by diatom aggregates, Trichodesmium spp., or detritus. Variations in OPC estimates of abundance are well explained by diel behavior and seasonal cycles of species that dominate mesozooplankton abundance, of which 80% are copepods. The summer maximum in mesozooplankton abundance is due primarily to the increase of the six smallest OPC size classes (< 1.15 mm equivalent spherical diameter), dominated by 14 nonmigrating copepod species that account for more than 95% of average copepod abundance. Seasonal cycles of zooplankton egestion estimated from OPC measurements were highly correlated, and comparable in magnitude, with observed sinking flux measurements of both C and N. Sinking flux at the base of the euphotic zone was 0.67 and 0.77 mol C m(-2) yr(-1) and 81 and 87 mmol N m(-2) yr(-1), for 1995 and 1995, respectively. The potential contribution of mesozooplankton egestion in the mixed layer, based on OPC measurements, accounts for 95% and 90% of C and 86% and 81% of N, respectively.

Scheinberg, RD, Landry MR, Calbet A.  2005.  Grazing impacts of two common appendicularians on the natural prey assemblage of a subtropical coastal ecosystem. Marine Ecology-Progress Series. 294:201-212.   10.3354/meps294201   AbstractWebsite

The clearance rates of co-occurring appendicularian species, Oikopleura longicauda and O. fusiformis, in Kaneohe Bay, Hawaii, were investigated to evaluate and compare their roles in a tropical food web. Individual appendicularians were captured in situ and allowed to feed on the natural plankton assemblage for 60 to 180 min. Feeding rate estimates were based on flow-cytometry analyses of cell-density changes for heterotrophic bacteria (Hbact), Synechococcus spp. (Syn) and < 13.0 mu m autotrophic eukaryotes (Aeuks), Despite morphological differences, O. longicauda and O. fusiformis cleared the largest prey size-fraction at statistically indistinguish able rates. For the 3 prey categories (Hbact, Syn and Aeuks), mean clearance rates (+/- 95% CI) were 12 +/- 7, 27 +/- 6 and 34 +/- 18 ml individual (ind.)(-1) h(-1) and 25 +/- 12, 26 +/- 15 and 38 +/- 20 ml ind.(-1) h(-1) for O. longicauda and O. fusiformis, respectively, The mean clearance rates of these 2 species on total sub-micron cells in Kaneohe Bay were not significantly different; however, O. fusiformis cleared Hbact at a marginally higher rate (p = 0.07). Only O. longicauda exhibited significantly different retention efficiencies as a function of prey size, clearing the smallest prey (Hbact) at approximately 36 % the rate of the largest (Aeuks) (p < 0.01). Despite reduced efficiencies on the smallest prey categories, at high abundances in Kaneohe Bay (often 2 ind. l(-1)), O. longicauda is capable of removing > 60%, of the picoplankton standing stock from the water column daily. While generally much less abundant, during occasional peaks of 1 ind. l(-1), O. fusiformis can remove an almost equivalent amount (> 50%). Nevertheless, the consistently higher abundances of O. longicauda make this species a more significant link between picoplankton production and higher-level consumers (chaetognaths and fishes) in this coastal tropical embayment.

Bollens, GCR, Landry MR.  2000.  Biological response to iron fertilization in the eastern equatorial Pacific (IronEx II). II. Mesozooplankton abundance, biomass, depth distribution and grazing. Marine Ecology-Progress Series. 201:43-56.   10.3354/meps201043   AbstractWebsite

Mesozooplankton (202 to 2000 mu m) biomass, abundance, taxonomic composition, depth distributions and gut pigment contents were measured inside and outside of an iron-enriched patch during the IronEx II study in the eastern equatorial Pacific. Mean carbon biomass remained nearly constant in the ambient community, but increased 2- to 3-fold during early stages of the phytoplankton bloom. The increases were due primarily to small calanoid and cyclopoid copepods and copepod nauplii in the mixed layer and appeared to be the result of 2 processes. First, significantly higher abundances of nauplii in the patch indicated that adult copepods responded reproductively, at least initially, to the increased food. Second, changes in copepod vertical migratory behaviors in response to reduced light penetration and increased food abundance in the patch apparently resulted in an upward displacement of copepods from the lower euphotic zone into the mixed-layer. Mesozooplankton gut pigment content also increased significantly inside the patch, largely in proportion to the increased concentration of phytoplankton chlorophyll a, and estimates of carbon consumed suggest that mesozooplankton standing stock was growing at maximal, or near maximal, temperature-dependent rates (1.0 d(-1)) at the peak of the patch bloom. Nonetheless, zooplankton abundance and biomass declined, rather than increased, during this period. The premature decline of mesozooplankton in the patch suggests that they might have been cropped by their predators in a tightly coupled trophic network or that their reproductive output may have failed to produce viable young when the food resources were dominated by diatoms.