Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web

Abstract

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-µm cells) with especially high concentrations of spp, we found high mesozooplankton biomass (∼5 g dry weight m) and grazing impact (12-50% integrated water column chlorophyll ), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll 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 SiO 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.

Nitrogen and Isotope Flows Through the Costa Rica Dome Upwelling Ecosystem: The Crucial Mesozooplankton Role in Export Flux

“…The relatively higher importance of fish fecal pellets in sinking derives from high remineralization rates of mesozooplankton fecal pellets in the euphotic zone (loss terms including microbial degradation, dissolution to DOM, and consumption by mesozooplankton). Substantial remineralization of mesozooplankton fecal pellets within the euphotic zone is also supported by in situ data, which show that phaeopigment flux into sediment traps accounts for only a small fraction of the phaeopigments produced by mesozooplankton grazing (Décima et al, ; Stukel, Décima, et al, ).…”

“…Biomass of nonpigmented protists was quantified by a combination of epifluorescence microscopy for nanoflagellates and dinoflagellates and light microscopy for ciliates (Freibott et al, ). Mesozooplankton were sampled with paired day‐night oblique net tows through the euphotic zone with a 1‐m ring net with flow meter and time‐depth recorder (Décima et al, ). The resulting samples were size fractionated (0.2–0.5, 0.5–1, 1–2, 2–5 and >5 mm) and split for biomass or gut fluorescence (herbivorous grazing) assessments.…”

“…(e) Picophytoplankton biomass/total phytoplankton biomass (Selph et al, ; Taylor et al, , ). (f) Mesozooplankton biomass (Dam et al, ; Décima et al, , ; Roman et al, ; Roman & Gauzens, ). Replicate bars are results from different Lagrangian experiments (CRD) and different cruises (EB and EqPac).…”

“…While new production and the f ratio (ratio of new production to total primary production) were high (in fact, higher than in the equatorial Pacific), sinking particle export was quite low, with export ratios ( e ratio = export/primary productivity) less than 0.05 (Figures b–d, Stukel et al, ). Also, despite the dominant role of SYN in the region, mesozooplankton biomass was substantially higher than in the equatorial Pacific (Dam et al, ; Décima et al, , ; Roman et al, ). The food web structure and ecosystem pathways necessary to support this surprisingly low export and high mesozooplankton biomass are currently unknown and provide the motivation for the present constrained model analysis.…”

Evaluating the Potential Impacts of the Diurnal Vertical Migration by Marine Organisms on Marine Biogeochemistry

“…Most of the available observations concern mesozooplankton and/or micronekton, such that in the database, only very few data points refer to the whole community. References from which the database is derived are as follows: Rodier and Le Borgne (); Yamaguchi et al (); Smeti et al (); Haury et al (); Cook et al (); Head et al (); Allison and Wishner (); Madhupratap et al (); Décima et al (); Yebra et al (); Putzeys et al (); Roman et al (); Le Borgne et al (); Martin and Christiansen (); Décima et al (); Hays, Harris, et al (); Hernández‐León et al (); Steinberg, Cope, et al (); Dam et al (); Champalbert et al (); Champalbert et al (); Kitamura et al (); Landry et al (); Hidaka et al (); Madin et al (); Timonin (); Pal et al (); Marlowe and Miller (); Smith et al (); Perissinotto and McQuaid (); Inoue et al (); Hopkins (); Ward et al (). The database includes 96 data points.…”