The macrobenthos of the Little Lagoon, Durban Bay.
The Little Lagoon is a shallow sandflat habitat situated in Durban Bay, which has been earmarked for removal, as part of the port expansion. In order to prevent the possible loss of such a significant habitat, it was proposed that this habitat be re-created elsewhere in the Bay. The aims of this project were therefore to provide a detailed assessment of the macrobenthic habitat of the Little Lagoon, and to identify the major determinants of the community structure. The ultimate goal was to provide essential background information to assess the success of the recreation of the Little Lagoon. Apart from seasonal changes in water temperature, no ecologically significant temporal fluctuations in the physical environment of the Little Lagoon were detected. This was directly translated into an extremely stable macrobenthic community, in which negligible seasonal changes to its composition were recorded. The polychaetes Prionospio sexoculata, Glycera sp, the isopod Leptanthura laevigata and cumaceans dominated the community during every sampling season. From a spatial perspective, particle sizes and organic contents of surficial sediments were the major determinants of macrobenthic community structure. Densities of macrofauna were three to five times higher in organically rich sediments, and were dominated by surface and sub-surface deposit feeders such as the tanaid Apseudes digitalis and cirratulid polychaetes. In organically poor sediments, burrowing infauna such as Prionospio sexoculata and Glycera sp. dominated. Significantly though, biological interactions, specifically bioturbation by the sandprawn Callianassa kraussi, was an important determinant of community structure in the Little Lagoon. Two zones of high and low abundance of C. kraussi were recorded in the Little Lagoon. Abundance, species richness and diversity of macrofauna were significantly lower in the zone of high C. kraussi abundance. These parameters were significantly and negatively influenced by the abundance of C. kraussi, indicating that C. kraussi may act as a disturbance organism. Surface dwelling macrofauna were recorded in the zone of low C. kraussi abundance, but not in the zone of high C. kraussi abundance. It appeared that the bioturbative activity of C. kraussi of expelling sediment from burrows to the sediment surface resulted in the exclusion surface dwelling fauna, and played a major role in structuring the Little Lagoon macrobenthic community.