Factors affecting respiration and photosynthesis by the benthic community of a subtical siliceous sediment

In a shallow, subtidal, siliceous sediment, benthic microalgal biomass (g chlorophyll a cm^-3) is influenced by light and physical sediment dynamics. The microalgal community is relatively dense, despite adverse conditions (7.0 g chlorophyll a cm^-3), and is able to respond rapidly to favorable conditions. Productivity of this community is significantly correlated (P0.05) with benthic light. In addition, productivity is influenced by temperature and bottom water NH₄ ⁺ and PO₄ ^-3 concentrations, especially as the concentrations fall to levels approaching the K _s (halfsaturation constant) of the microalgal community. Metabolic activity in this environment is dependent upon a continuous supply of organic carbon. Temperature is significantly correlated with respiration rate, but other factors (e.g. biomass and organic matter supply) are important also. Community respiration responds to overlying phytoplankton productivity in the same manner as deep-water benthic environments. Bacterial enumeration using CFU (colony-forming units) does not measure accurately the number of in situ metabolically active bacteria.This research was supported by Energy Research and Development Administration Contract AT (11-1) 3279, US AEC Contract AT (11-1) GEN 10, P.A. 20 and NOAA Sea Grant No. 04-3-158-22.