DISSOLVED AND PARTICULATE MATTER IN THE SURFACE WATERS OF FALSE BAY AND ITS INFLUENCE ON A ROCKY SHORE ECOSYSTEM

SUMMARY

An analysis was made of dissolved and particulate matter in the surface waters of False Bay. Under conditions of strong, sustained south-easterly winds there was evidence of offshore upwelling of cooler, nitrate-rich water, which resulted in large phytoplankton standing stocks; chlorophyll α levels in excess of 10 μg.ℓ⁻¹ were recorded within 0,5 km of the shore. In the absence of these winds, nitrate concentrations and phytoplankton stocks were low in the offshore waters. Regardless of the wind, the particulate matter in shore was dominated by much unidentifiable detritus. It is concluded that the large biomass of filter feeders on the intertidal and subtidal reef at Dalebrook depends primarily on energy derived from detritus produced in the inshore waters and associated bacterial decomposers. The influence of upwelling, resulting in phytoplankton being driven in shore, is of minor importance to this benthic community.