Prawn community structure in the subtropical Mfolozi-Msunduzi estuarine system, KwaZulu-Natal, South Africa

The life cycles of many marine and freshwater prawn species are closely associated with estuarine habitat. Here, the prawn community of the Mfolozi-Msunduzi estuarine system is described and the system's potential as an alternative nursery for prawns during prolonged closure of the adjacent St Lucia estuarine system is examined. Sampling was conducted at five localities in summer and winter in 2007-2012. The Mfolozi-Msunduzi Estuary is a river-dominated system with mouth condition, sediment grain size and turbidity being the most important factors affecting the structure of its prawn community. Twelve prawn species were recorded, including five marine penaeid and five freshwater palaemonid species. The prawn community was numerically dominated by freshwater Macrobrachium equidens and two penaeids, Fenneropenaeus indicus and Metapenaeus monoceros. Significant differences were recorded between summer and winter samples, with freshwater species dominating the catch in summer, while penaeid species were dominant in winter. The marked seasonal change in the prawn community was related to strong river flows during summer creating low-salinity conditions, unsuitable for penaeid postlarval development, throughout most of the system. Compared to St Lucia, the Mfolozi-Msunduzi Estuary can be regarded as a poor alternative nursery area for penaeids during the summer peak postlarval recruitment period.