Grazing processes and secondary production in the Arabian Sea: A simple food web synthesis with measurement constraints

Landry, MR.  2009.  Grazing processes and secondary production in the Arabian Sea: A simple food web synthesis with measurement constraints. Indian ocean biogeochemical processes and ecological variability. ( Wiggert JD, Hood RR, Naqvi SWA, Brink KH, Smith SL, Eds.).:133-146.: American Geophysical Union, Washington, DC (USA)


ASFA 1: Biological Sciences & Living Resources, Biogeochemical cycle, ecosystems, food webs, grazing, ISW, Arabian Sea, marine, Q1 01481:Productivity, secondary production, Trophic structure, zooplankton


The Joint Global Ocean Flux Study in the Arabian Sea during the mid 1990s provides a rare opportunity to elucidate carbon flows in the lower food web of an open ocean ecosystem. Analysis of that data to date has, however, produced widely divergent perspectives on major flux pathways and roles of zooplankton: from zooplankton as controlling grazers tightly coupled to microbial processes to zooplankton as casual consumers who let a large fraction of production, mostly generated by picophytoplankton, flow directly to detritus and export. Synthesis of experimental grazing rates and production inferences for mesozooplankton and microzooplankton fit well in a conceptually simple food web, constrained by measured carbon flows through phytoplankton and bacteria. Microzooplankton dominate grazing processes, consuming over 70% of particulate primary production (PP), on average, and providing steady and significant supplemental nutrition to mesozooplankton. Direct grazing estimates of mesozooplankton, on the order of 25% of PP, are sufficient to balance the remaining particulate production, with additional transfer through a one- to two-step food chain of microzooplankton accounting for a total ingestion of 6 40% of PP required for mesozooplankton secondary production. Dissolved organic carbon fluxes to bacteria are provided mostly within the constraints of gross and net primary production. Contradictory results from inverse models are likely due to an assumption that exaggerates by approximately twofold the production contribution of picophytoplankton and to the failure to use measured rates of gross primary production as a system constraint. Grazing generally balances net particulate primary production in the Arabian Sea, but true grazer control of phytoplankton dynamics remains an open issue for further study.