BIOMASS AND PRODUCTION OF BENTHIC MICROALGAL COMMUNITIES IN ESTUARINEHABITATS

Accurate. measures of intertidal benthic microalgal standing stock (bi omass) and productivity are needed to quantify their potential contrib ution to food webs. Oxygen microelectrode techniques, used in this stu dy, provide realistic measures of intertidal benthic microalgal produc tion. By dividing a salt-marsh estuary into habitat types, based on se diment 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 i n five different estuarine habitats over an 18-mo period to document t he relative contributions of benthic microalgal productivity in the di fferent habitat types. Samples were collected bimonthly from April 199 0 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 sh allow subtidal habitats the lowest (60.4 +/- 8.9 SE) microalgal biomas s. There was a unimodal peak in biomass during the late winter-early s pring period. The concentrations of photopigments (Chl a and total phe opigments) in the 0-5 mm of sediments were highly correlated (r2 = 0.7 3 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. bioma ss (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communit ies (r2 values ranged from 0.43 to 0.73). The habitat approach and oxy gen microelectrode techniques provide a useful, realistic method for u nderstanding the biomass and production dynamics of estuarine benthic microalgal communities.