A Contribution to the ecology of the Umlalazi Estuary

Abstract

The UmIalazi river in Zululand is undergoing large scale changes due to deposition of mud from cultivated areas and a simultaneous rapid colonisation by mangroves chiefly Avicennia officinalis. The result is that open mud banks are being consolidated, shallows are changing into mangrove swamps and eventually into dry land. Much useful information can, be obtained from the study of aerial photographs and in the case of the Zululand coastal rivers we are fortunate in having two series of photographic surveys by the Trigonometrical survey. The photographs of the Umlalazi were made in 1937 and in 1960 and are reproduced in Fig. 1. The spread of mangroves and mud banks is obvious. In view of these changes it was felt that an ecological survey should be undertaken in order to record the present physical conditions and animal life in the estuary. As the mangrove invasion progresses the estuary will become narrower, shallows will disappear and tidal currents will become stronger. This should result in an increase in the fauna associated with mangrove swamps and a decrease in the shallow water fauna.

Zoologica Africana 2 (1): 1-24