Fish as indicators of diving and fishing pressure on high-latitude coral reefs

Abstract

Despite the proclamation of South Africa's coral reef marine protected areas (MPAs) more than 20 years ago, the effects of human activities on the fish communities have not been investigated. This study used a multi-species Fish-index to compare ecological indicators such as biomass, abundance, trophic structure and reproductive potential between multiple-use and no-take sanctuary zones. Seven study reefs were surveyed; six in South Africa and a non-MPA reef in southern Mozambique. Randomly stratified underwater visual censuses (UVC) using the point count technique were used to survey fish communities. Environmental variables and habitat characteristics were also recorded. Nonmetric multidimensional scaling ordinations were similar for abundance and biomass trends and revealed a high degree of overlap between all zones, except for the no-take Sanctuaries. The latter formed discrete clusters and were significantly different (Analysis of Similarity) to the other zones. Total abundance and biomass were highest in the Sanctuary zones and lowest in the Open zone. Differences in trophic composition between zones were largely due to predatory species. This was supported by similarity percentages analysis (SIMPER) which identified six discriminating species. Length-frequency analysis of these species revealed consistent trends with higher numbers of large individuals in the Sanctuary zones and reduced numbers of small individuals in zones open to human activity. These results along with those of the Generalised Linear Models (GLM) demonstrate that human activities are affecting the southern African coral reef fish communities. Marginal differences between the multiple-use MPA zones on the South African reefs and the non-MPA reef in southern Mozambique suggest that MPA management objectives require re-evaluation.