Contributions of the Plankton Community to Ecosystem Respiration, Tomales Bay, California

This paper presents direct measurements of plankton community respiration for Tomales Bay, California, U.S.A., and compares these measurements with water column variables. These data were used to develop a regression model that predicts planktonic respiration and nutrient remineralization. Respiration was measured as change in dissolved O2in sealed, dark, 300 ml bottles. There was a consistent and linear decrease in O2concentrations over 35–48 h incubations. Chlorophyllaconcentration ranged from 1 to 10 μg chl a l−1. Bacterial counts were 2–11×106cells ml−1and leucine incorporation rates ranged from 200 to 1300 pmol l−1h−1over the period May 1992–July 1993. Respiration rates were 0•16–1•91 μmol O2l−1h−1, with an annualized average of 0•67 μmol O2l−1h−1. A multiple linear regression of O2consumption rate against the independent variables (chlorophyll concentration, temperature and particulate N concentration) explained 79% of the variation in the respiration rates. Modelled plankton community respiration rates for the period January 1988 to July 1993 ranged from <0•4 to >2•0 μmol O2l−1h−1. Over the same period, the average predicted areal respiration for inner Tomales Bay was 64•5 mmol O2m−2day−1. Mean predicted rates of N and P remineralization over the period of January 1988 to July 1993 were 9•8 and 0•6 mmol m−2day−1, respectively. Even in an embayment as shallow as Tomales Bay (meanz=3•1 m), planktonic respiration and remineralization are greater than benthic respiration and remineralization.