Grazing and Dynamics of Grazer Populations in a Temperate Fjord

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In Dabob Bay (Washington), a temperate fjord, the annual cycles of phytoplankton standing stock and production rate exhibit spectacular increases (phytoplankton blooms) in spring and autumn, indicating lack of control by grazer populations. Yet virtually all organic matter produced by the phytoplankton during blooms is ultimately consumed by grazers. Moreover, a major fraction of the grazing (about 67% on an annual basis) appears to be due to macrozooplankton suspension-feeders, with microzooplankton being secondary grazers. A conceptual model of grazing in Dabob Bay was developed, hypothesizing the identities of the macro- and microzooplankton grazers and postulating mechanisms for the approximate annual balance between phytoplankton growth and grazing. A field test of the conceptual model was developed and carried out on three extended research cruises to Dabob Bay in 1990-91. This project will complete the analysis of samples and data, and produce a synthesis. By direct measuerements this study will provide quanitative assessment of mechanisms and rates of processes governing the dynamics of phytoplankton production and its fate in a highly productive coastal pelagic ecosystem.