BIOMASS AND PRODUCTION OF BENTHIC MICROALGAL COMMUNITIES IN ESTUARINE HABITATS

Accurate. measures of intertidal benthic microalgal standing stock (biomass) and productivity are needed to quantify their potential contribution to food webs. Oxygen microelectrode techniques, used in this study, provide realistic measures of intertidal benthic microalgal production. By dividing a salt-marsh estuary into habitat types, based on sediment and sunlight characteristics, we have developed a simple way of describing benthic microalgal communities. The purpose of this study was to measure and compare benthic microalgal biomass and production in five different estuarine habitats over an 18-mo period to document the relative contributions of benthic microalgal productivity in the different habitat types. Samples were collected bimonthly from April 1990 to October 1991. Over the 18-mo period, tall Spartina zone habitats had the highest (101.5 mg chlorophyll a (Chl a) m-2 +/- 6.9 SE) and shallow subtidal habitats the lowest (60.4 +/- 8.9 SE) microalgal biomass. There was a unimodal peak in biomass during the late winter-early spring period. The concentrations of photopigments (Chl a and total pheopigments) in the 0-5 mm of sediments were highly correlated (r2 = 0.73 and 0.88, respectively) with photopigment concentrations in the 5-10 mm depth interval. Biomass specific production (mumol 0, mg Chl a-1 h-1) was highest in intertidal mudflat habitats (206.3 +/- 11.2 SE) and lowest in shallow subtidal habitats (104.3 +/- 11.1 SE). Regressions of maximum production (production at saturating irradiances) vs. biomass (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communities (r2 values ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic method for understanding the biomass and production dynamics of estuarine benthic microalgal communities.