Physico-chemical characteristics of South African estuaries in relation to the zoogeography of the region

Selected physico-chemical characteristics of estuaries within three biogeographic regions of South Africa were described and compared using data from an extensive ichthyological survey of the region. The results indicate that estuaries within each zoogeographic region have distinctive physico-chemical characteristics that could be related to regional variations in climate and oceanographic conditions. Estuarine temperatures follow the trend for marine coastal waters, decreasing from the subtropical east coast, along the warm-temperate south coast and up the cool-temperate west coast. Low rainfall and runoff together with high seawater input and evaporative loss results in high salinities and low turbidities in warm-temperate estuaries while high rainfall and runoff results in reduced salinities and high turbidities, particularly in subtropical estuaries.