Distribution and abundance of benthic microalgae in a shallow southwestern Australian estuarine system

Measurements were made of benthic microalgal biomass (chlorophyll mg m-2) and concentration (chlorophyll, µg g-1 dry weight of sediment) from the Peel-Harvey estuarine system, Western Australia. Most chlorophyll was in the top 1 cm of sediment, and less than 10 % of chlorophyll a was non-functional as determined by hexane extraction. Highest biomass occurred at shallow sites and on coarse sandy sediments. Biomass was higher in Harvey (202 mg m-2) than Peel (107 mg m-2) in summer when there was a large population of microalgae in Peel; biomass was similar in winter (Harvey 163 mg m-2, Peel 151 mg m-2). Biomass increased with the onset of riverine nutrient input and decreased when blooms occurred in the water column. Except during Nodularia blooms, the biomass (chlorophyll) of benthic microalgae greatly exceeded (e g 40 times) the biomass of chlorophyll in the water column above. In summer much of the chlorophyll of the water column was due to wind stirring of benthic microalgae. The possible importance of benthic microalgae to the productivity of shallow systems is emphasized