The Ecology of the Plants and Animals in the Intertidal Regions of the Zwartkops Estuary Near Port Elizabeth, South Africa

Abstract

Estuary of Zwartkops river which enters Algoa Bay on the n.-e. outskirts of Port Elizabeth is permanently open to sea; it has associated with it, particularly in the lower reaches, extensive salt marshes. Distribution of flora and fauna in intertidal area has been studied throughout the length of the estuary; particular attention having been given to salt marshes near the mouth. Distribution of animals along the estuary is controlled by (1) almost complete absence of a salinity gradient, (2) deposition of a thin layer of fine silt on all surfaces and (3) a change in configuration of banks which in upper and middle reaches become very high and force the channel into narrow confines. First description of plant zonation on a South African salt marsh is given. Five zones are recognized (1) a Zosteretum (2) a Spartinetum stricta (3) an Arthrocnemetum perenne (4) a Limonietum and (5) an Arthrocnemetum of shrubby spp. These are used as markers in description of faunal zonation which is more complex and less precise. Certain animal communities, notably those dominated by Calianassa, by Upogebia, by Alpheus and by Cleistostoma, are described in detail. Attention is given to compiling a food web and to a study of commensalism. Zonation of both animals and plants is compared with Stephenson classification of rocky shores.