Biomass and composition of protistan grazers and heterotrophic bacteria in the Costa Rica Dome during summer 2010.
We investigated biomass and composition of heterotrophic microbes in the Costa Rica Dome during June-July 2010 as part of a broader study of plankton trophic dynamics. Because picophytoplankton (<2 μm) are known to dominate in this unique upwelling region, we hypothesized tight biomass relationships between size-determined predator-prey pairs (i.e. picoplankton-nano-grazers, nanoplankton-micro-grazers) within the microbial community. Integrated biomass of heterotrophic bacteria ranged from 180 to 487 mg C m-2and was significantly correlated with total autotrophic carbon. Heterotrophic protist (H-protist) biomass ranged more narrowly from 488 to 545 mg C m-2, and was comprised of 60% dinoflagellates, 30% other flagellates and 11% ciliates. Nano-sized (<20 μm) protists accounted for the majority (57%) of grazer biomass and were positively correlated with picoplankton, partially supporting our hypothesis, but nanoplankton and micro-grazers (>20 μm) were not significantly correlated. The relative constancy of H-protist biomass among locations despite clear changes in integrated autotrophic biomass, Chla, and primary production suggests that mesozooplankton may exert a tight top-down control on micro-grazers. Biomass-specific consumption rates of phytoplankton by protistan grazers suggest an instantaneous growth rate of 0.52 day-1for H-protists, similar to the growth rate of phytoplankton and consistent with a trophically balanced ecosystem dominated by pico-nanoplankton interactions.
Scripps Institution of Oceanography , University of California at San Diego , 9500 Gilman Dr., La Jolla, CA , USA.
Alexandra
A
Freibott
Scripps Institution of Oceanography , University of California at San Diego , 9500 Gilman Dr., La Jolla, CA , USA.
Andrew G
AG
Taylor
Department of Oceanography , University of Hawaii at Manoa , Honolulu, HI , USA.
Karen E
KE
Selph
The Hong Kong University of Science and Technology , Hong Kong Sar , China.
Hongbin
H
Liu
Institute of Oceanography, Chinese Academy of Science , Qingdao , China.
Wuchang
W
Zhang
Scripps Institution of Oceanography , University of California at San Diego , 9500 Gilman Dr., La Jolla, CA , USA.
Michael R
MR
Landry
community composition; heterotrophic protists; microzooplankton; nanozooplankton