Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web.
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 ofSynechococcusspp., we found high mesozooplankton biomass (∼5 g dry weight m-2) and grazing impact (12-50% integrated water column chlorophylla), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyllaand 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 SiO2production (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.
Scripps Institution of Oceanography, 9500 Gilman Dr., LA Jolla, CA 92093-0227, USA; Present Address: National Institute of Water and Atmospheric Research (NIWA), 301 Evans Bay Parade, Hataitai 6021, Wellington, New Zealand.
Moira
M
Décima
Scripps Institution of Oceanography , 9500 Gilman Dr., LA Jolla, CA 92093-0227 , USA.
Michael R
MR
Landry
Department of Earth, Ocean, and Atmospheri Science , Florida State University , Tallahasee, FL 32306 , USA.
Michael R
MR
Stukel
Ieo Centro Oceanografico De Santander , Promontorio San Martin S/N, 39004 Santander-Cantabria , Spain.
Lucia
L
Lopez-Lopez
Dauphin Island Sea Lab , 101 Bienville Blvd, Dauphin Island, AL 36528 , USA.
Jeffrey W
JW
Krause
OMZ; efficiency; food chain; secondary production; trophic transfer