FINE-SCALE VERTICAL RESOLUTION OF CHLOROPHYLL AND PHOTOSYNTHETIC PARAMETERS IN SHALLOW-WATER BENTHOS

The vertical distributions of chlorophyll concentration and photosynth etic 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 millimeter that contained as much as or more chlorophyll than the 0.2 to 0.6 m of water overlyi ng them. The photosynthetic responses of the sediment-associated micro algae were comparable with those of the suspended phytoplankton. Below the surficial floc, constancy of chlorophyll concentration and photos ynthetic-irradiance (PI) responses indicated the existence of a physic ally mixed layer in the underlying 8 to 15 mm. Photosynthetically comp etent algae were found below the mixed layer and well below the depth to which Light penetrates the sediment (ca 1 mm). Primary production w as more or less equally distributed between the surficial millimeter o f benthos and the overlying water. The surficial flee and some of the underlying sediment may be readily resuspended so that 'benthic' micro algae can contribute significantly to both water column and benthic pr imary production.