Diversity and distribution of subtidal soft-bottom macrofauna of the Isimangaliso Wetland Park, South Africa.

Abstract

There have been no previous studies describing the subtidal soft-bottom macrofaunal assemblages of the iSimangaliso Wetland Park or how they are influenced by the ecological and environmental processes associated with coral reef proximity. With South Africa having high wave energy the transportation of nutrients and organisms between the soft-bottom areas and reef habitats is probable. This transfer of resources may create ecological linkages which organisms depend on. The aim of this study was to document the species diversity, distribution and abundance of in- and epi-macrofauna in iSimangaliso Wetland Park and to relate these to depth, sediment grain size, location, reef proximity and protective status. Macrofauna were collected using an air-lift design suction sampler. The macrofauna were identified to the lowest possible taxonomic level, biomass estimates were calculated and sediment grain size was determined. A total of 5166 animals were collected and 121 macrofauna species were identified. Macrofaunal assemblages inhabiting the soft-bottom sedimentary habitat surrounding the reefs changed in species abundance and diversity with increasing distance from the reef. Lower abundances and diversity were found closest to the reefs strongly indicating that the macrofaunal assemblages were negatively affected by the reef proximity. Although reef proximity was indicated as influential, environmental gradients were found to be more important in defining community structure. Higher percentages of coarse sediments found closest to the reef edge coincided with lower abundances, biomass and species richness of macrofauna. Trends of higher abundances at the middle distance indicated hydrodynamic disturbance may be affecting near shore assemblages. Sediment grain size and hydrodynamic disturbance both appeared to be the main determinants of assemblage structure around reefs. Trophic interactions by reef associated predators were indicated by lower macrofaunal abundances recorded at close proximity to the reefs.There was no evidence for the presence of a latitudinal diversity gradient as localised environmental conditions were found to be more influential in determining soft-bottom macrofaunal community structure and distribution in the iSimangaliso Wetland Park. The presence of ecological linkages between soft-bottom macrofaunal communities and coral reefs gives insight into the important roles soft-bottom macrofauna play in the functioning of the iSimangaliso Wetland Park marine reserve. The documentation of the species diversity and distribution of macrofauna in the soft-bottom habitats will provide valuable baseline information for the future management strategies.