THE RELATIVE CONTRIBUTION OF BENTHIC MICROALGAE TO TOTAL MICROALGAL PRODUCTION IN A SHALLOW SUBTIDAL ESTUARINE ENVIRONMENT

This study examined the contribution of benthic microalgae to total mi croalgal production in the Weeks Bay National Estuarine Research Reser ve, a shallow subtidal estuarine ecosystem in Baldwin County, Alabama, USA. Environmental characteristics, nutrient concentrations, and bent hic and planktonic biomass and productivity rates were measured every 2-4 weeks between February 1991 and August 1992. Chlorophyll-a concent rations in the surficial sediments ranged from 0.2 to 30.7 mg m(-2), w ith a mean of 9.5 +/- 1.5 mg m(-2) for the study period. Over an annua l cycle, benthic microalgae contributed 25.2% of total microalgal biom ass. Daily production rates for the benthic microalgae ranged from 0.0 1 to 0.75 gC m(-2) d(-1), with a mean of 0.22 +/- 0.05 gC m(-2) d(-1). Annual production of the benthic microalgae was 90.1 gC m(-2), or 20. 6% of total microalgal production in Weeks Bay. Stepwise multiple regr ession revealed that nitrate, planktonic chi-a, benthic production, an d seston accounted for 33% of the variability in benthic microalgal bi omass, while light, seston, nitrate and benthic chi-a accounted for 36 % of the variability in benthic microalgal production. This study sugg ests that, in this environment, the relative importance of benthic mic roalgal production is not regulated by any single factor, but rather i s highly variable as a result of physical mixing and resuspension proc esses.