Zooplankton composition and copepod lipid content over Fall 2014 in the Salish Sea

Abstract

Zooplankton are secondary producers that play a major role in carbon sequestration, the microbial loop, and energy transfer across trophic levels. Zooplankton are abundant in the Salish Sea, a productive inland sea with a complex estuarine circulation that is subject to seasonal physical processes. We studied the zooplankton composition in the Salish Sea and measured the relation of biotic factors to water properties. We estimated zooplankton abundance and diversity in the San Juan Channel and compared to broader Salish Sea and five physical factors (temperature, salinity, dissolved oxygen, fluorescence, and dissolved inorganic carbon). The most abundant zooplankton in the Salish Sea was calanoid copepod. However, copepod nauplii were more abundant at North station during the beginning of the sampling period. The fall transition marked a steady zooplankton density decrease. Salinity and dissolved oxygen had a strong correlation with total zooplankton abundance, copepod abundance, and % of copepods with lipid content. Zooplankton abundance and composition in late October reflected how downwelling conditions and river flow, among other oceanographic variables, greatly affect spatial zooplankton distribution. The spatial variation of zooplankton, influenced by tides and the fall transition, was pronounced in the estuary and may be due to different water properties at the sampled stations.