Fine-scale vertical resolution of chlorophyll and photosynthetic parameters in shallow-water benthos

Abstract

The vertical distributions of chlorophyll concentration and photosynthetic parameters of sediment-associated microalgae were measured with a resolution of 1 mm. Sediment and the overlying water were sampled at 3 sandy, shallow-water sites near Corpus Christi Bay, Texas, USA. All sediment samples had a floc in the surficial rmllimeter that contained as much as or more chlorophyll than the 0.2 to 0.6 m of water overlying them. The photosynthetic responses of the sediment-associated microalgae were comparable with those of the suspended phytoplankton. Below the surficial floc, constancy of chlorophyll concentration and photosynthetic-irradiance (PI) responses indicated the existence of a physically mixed layer in the underlying 8 to 15 mm. Photosynthetically competent algae were found below the mixed layer and well below the depth to which light penetrates the sediment (ca 1 mm).