Benthic faunal distribution and abundance in the Mfolozi-Msunduzi estuarine system, KwaZulu-Natal, South Africa

The Mfolozi-Msunduzi estuarine system historically shared a common mouth with the St Lucia estuarine system. In 1952, a separate mouth was created, 1.5 km south of St Lucia mouth, to prevent silt carried by the Mfolozi River from entering Lake St Lucia. Despite its proximity to the comparatively well-studied St Lucia Estuary, there is very little information on the Mfolozi- Msunduzi estuarine system in general and no information on its benthos. In the present study, 17 taxa were recorded from biannual quantitative sampling in 2007 and 2008. Results indicated that the system was dominated by the polychaetes Ceratonereis sp., Dendronereis arborifera and Capitella capitata, the crab Paratylodiplax blephariskios and the tanaid Apseudes digitalis. The main factors influencing the distribution of the benthos were oxygen concentration, temperature, the open or closed state of the mouth, and salinity, with particle size and organic content of the substratum also being important in determining community structure. Although the dominant taxa were previously recorded as abundant in St Lucia, numbers present in the Mfolozi-Msunduzi system were generally lower than those recorded in St Lucia, suggesting that periodic flooding and the unstable nature of the sediments in the Mfolozi-Msunduzi prevented its benthos from attaining the densities recorded in the adjacent St Lucia Estuary. While the Mfolozi-Msunduzi system is classified as a river mouth, its benthos was more similar in composition to that of the Mhlathuze and Mlalazi estuaries, which are classified as an estuarine bay and a permanently open estuary, respectively. It is suggested that reclassification of the Mfolozi-Msunduzi system as a permanently open estuary would be more appropriate in terms of its benthos.