COMMUNITY STRUCTURE, DISTRIBUTION, AND STANDING STOCK OF BENTHOS, EPIBENTHOS, AND PLANKTON IN THE COLUMBIA RIVER ESTUARY

Secondary producers were sampled in the Columbia River estuary during the 1980-81 Columbia River Data Development Program (CREDDP) studies. Benthic infaunal macroinvertebrates were sampled in all estuarine zones and habitats with a grab sampler during a single estuary-wide survey. Epibenthic macro- and meiofauna were sampled monthly with epibenthic pump and sled, beach seine, and trawl in tidal flat, slope, and channel bottom habitats throughout the estuary. Zooplankton and larval fish were sampled monthly with oblique zooplankton net tows in the main channel. The distribution of secondary consumers coincided with division of the estuary into three salinity zones and six habitat types, where the principal physical and biological processes that influenced the distribution and assemblage structure of secondary consumers were: (1) river discharge; (2) river discharge and tidal flow interaction which created circulation and salinity patterns and turbidity maximum characteristics; and (3) benthic processes, such as sediment type and transport and geomorphology. Standing stocks of benthic infauna were highest in protected tidal flat habitats and were comparatively depressed in the Estuarine Mixing Zone of the estuary. Standing stocks of epibenthic and zooplankton organisms, in contrast, were concentrated within the Estuarine Mixing Zone.