Estuarine benthic microalgal communities, composed of a mixed assemblage of benthic diatoms, cyanobacteria, and chlorophytes, inhabit the intertidal and subtidal sediments of coastal systems. Benthic microalgae are a primary carbon source for estuarine food webs, are an important component in nutrient cycles, and function as sediment stabilizers. The purpose of this research was to construct an ecophysiologically-based production model for North Inlet Estuary, SC, USA. The approach was to characterize the habitat-specific properties of benthic microalgae, construct and validate the model, and subject the model to sensitivity analysis to determine the relative importance of model components.

The estuary was divided into a mosaic of 5 habitat types based on sediment type, sunlight exposure, and tidal elevation. Using stratified-random sampling methods, biomass (Chl a) and production measurements were obtained from each habitat type at bimonthly intervals during 1990-91. Photosynthetic rates were determined using oxygen microelectrodes and Chl a was quantified by HPLC and spectrophotometric methods. Short-term (hourly) variability in production was attributed to vertical migration by benthic diatoms in the upper 5 mm of sediments. A curvilinear regression model revealed that much of the short-term production variability could be attributed to changes in tidal and sun angles. Habitat-specific photophysiological characteristics were assessed using PI curves obtained from benthic microalgal communities in different in situ light environments. Based on PI and photopigment characteristics, benthic microalgae appeared to readily photoacclimate to the ambient light environment. The production model, which incorporated the habitat-specific photophysiological and behavioral responses to in situ conditions, provided estimates of annual in situ benthic microalgal production in each of the 5 habitat types. The main factors in the model were in situ irradiance, photophysiological response, vertical migration periodicity, and microalgal biomass. Comparisons of field-based areal (m^-2) production with model predicted areal production revealed a significant positive correlation (rư = 0.63) with a slope of 1.0, suggesting that the model provided both accurate and reliable estimates of benthic microalgal production. Annual estimates of habitat-specific production were multiplied by the area of each habitat type to determine total microalgal production for the entire estuary. Short Spartina zone habitats provided 58% of the total annual production, followed by intertidal mudflats (21%), tall Spartina zones (3%), shallow subtidal (11%), and intertidal sandflat (7%) habitats. The average annual benthic microalgal production for North Inlet estuary in 1990-91 was estimated to be 4079 tonnes C y^-1. When compared with other estuarine phototrophs, benthic microalgae provide more than one third of the primary production in this estuary.

The spatial distribution of meiofaunal herbivores was compared to the distribution of microalgae using spatial autocorrelation techniques to analyze spatial patterns. Meiofauna and microalgae have nearly identical spatial patterns and similar patch sizes, suggesting a common spatial linkage between meiofaunal grazers and microalgal resources.