Seasonal coupling between ciliate and phytoplankton standing stocks in the South Slough of Coos Bay,Oregon

The standing stocks of ciliates and phytoplankton together with physical variables (temperature and density) were measured biweekly from March 6, 1999, to March 22, 2000, in the marine-dominated region of the South Slough, the southern arm of the Coos Bay estuary (Oregon, United States). The abundance and biomass of naked ciliates correlated significantly with phytoplankton <5 μm (ultraphytoplankton) biomass throughout the sampling periods and with total phytoplankton biomass between October and march; possibly due to a compositional shift in the >5 μm phytoplankton fraction from diatoms in the spring-summer period to flagellates during this fall-winter period. Temperature could explain 49% of the variation of ultraphytoplankton and naked ciliate biomass across seasons and may be important in determining the rate of the ciliate numerical response to increases in ultraphytoplankton and its assimilation into ciliate biomass. High standing stocks of ciliates, their strong coupling with ultraphytoplankton across seasons, and the relatively higher contribution of ciliate carbon to the ciliate and >5 μm phytoplankton carbon pool in the October–March period suggest that ciliates are a significant component to the South Slough food web and may be particularly important during seasons of reduced phytoplankton biomass.