PRIMARY PRODUCTIVITY OF THE BOT RIVER ESTUARY, SOUTH AFRICA

SUMMARY

The primary production of the Bot River estuary, a large closed estuary on the south-western coast of South Africa has been estimated at 11 059 t dry mass y⁻¹. The main contributions to this value come from the submerged aquatic macrophytes (7 987 t dry mass y⁻¹ or 72% of total calculated production), reeds (1 503 t dry mass y⁻¹ or 14%), benthic diatoms (787 t dry mass y⁻¹ or 7%) and phytoplankton (782 t dry mass y-¹ or 7%). These four categories are believed to contribute over 90% of the primary production during periods of stability when the estuary is closed and full. Much of this production is not directly utilized by herbivores and forms the basis of a bacterial system producing very fine, organically rich material deposited on the estuary bed. Primary production is affected by mouth opening in a number of different ways including changes in volume of water, available surface area for attachment of macrophytes, and loss of macrophytes which are stranded or washed out to sea.