Ecology of southern African estuaries Part XI. Mngazana: a mangrove estuary in Transkei

Abstract

Mngazana is a rich estuary dominated by mangroves and containing a diversity of both invertebrates and fish. Its richness is mainly due to favourable physical conditions. The invertebrate fauna includes temperate, tropical, and subtropical species, predominating in the lower reaches, middle reaches and head respectively. The fish have affinities with the tropics in summer, while in winter many warm-temperate species increase in numbers. In comparison with the fauna of soft substrates, that of rocks has a higher percentage of stenohaline and estuarine forms, and a more restricted distribution. The rocky habitat in estuaries favours greater specialization with respect to salinity tolerance. A high percentage of the biomass of invertebrates in soft substrates consists of detritivores, and the biomass is related to the organic content of the substrate. Mangrove mud has the hlghest organic content and supports the highest biomass, but few species can tolerate the conditions there. Mangroves are probably the major primary producers in the system.