An evaluation of coral reef fish communities in South African marine protected areas.
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Date
2010
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Abstract
Differences in coral reef fish assemblages were investigated on six South African and one southern
Mozambican reef under varying management regimes. All of the South African reefs fall within
marine protected areas (MPA) but are zoned for differing types and intensities of human activity.
Reefs where no human activities are allowed were termed Sanctuaries, while those on which
restricted fishing and SCUBA diving are permitted were termed Protected. The reef in southern
Mozambique is subjected to unrestricted fishing and SCUBA diving and was consequently termed
Open.
This study consists of two parts. The first dealt with a community assessment which investigated
and provided baseline data on the trophic structure, density, and species diversity of fish
assemblages on each of the seven study reefs. The objective was to compare the aforementioned
metrics between reefs and thereafter compare them between the different protection zones. The
second part of this study focused on assessing the impacts of human activities using 25 fish
indicator species. These species were selected a priori based on their ecological importance and
sensitivity to human activity (fishing and diving). The selection process was then guided by the
results of the community assessment. The objective was to use these species as indicators of
recreational diving and fishing pressure in the different protection zones. Density, biomass and size
frequency analyses comprised the primary metrics in this assessment.
Randomly stratified underwater visual censuses (UVC) were used to collect the fish data and these
were conducted on reefs inhabited by a coral community considered to be the core community on
South Africa’s reefs in terms of biodiversity and coral cover. The fish community assessment
consisted of timed counts in which all non-cryptic fish species were quantified. Indicator species
counts employed the point count technique with a radius of 10 m. An average of 11 community
counts and an average of 62 point counts were conducted per reef. Various environmental variables
and habitat characteritics were recorded during the UVCs.
Multivariate analysis of the fish assemblages indicated that the fish community structure differed
significantly according to reef protection status. Sanctuary reefs were significantly different from
the Open reef in Southern Mozambique. Mean fish abundance was highest on Sanctuary reefs and
lowest on the Open reef. In terms of overall species diversity, a total of 284 species belonging to 50
families were recorded, this being comparable to other reefs in the WIO region. Six families
contributed more than 50% towards the fish community composition: Labridae, Acanthuridae,
Chaetodontidae, Lutjanidae, Pomacentridae and Serranidae. All predator categories were well
represented on Sanctuary reefs, while top-level predators were scarce on the High-Diving and the
Open reef. Generalised linear model (GLM) regression analysis indicated that human activities
were significant variables in accounting for the variance in fish community structure.
The total fish abundance and biomass of the selected indicator species were significantly higher in
Sanctuary zones and lowest in the Open zone. In addition, Sanctuary zones were characterised by
high numbers of large predators, while non-Sanctuary zones were characterised by higher
abundances of prey species. Target species were also larger and more abundant in Sanctuary zones.
The data revealed that recreational fishing and high diving intensity may be influencing the fish
community structure on southern African coral reefs, which was confirmed by GLM regression
analysis. Long-term monitoring of these fish communities is recommended to confirm the trends
observed in this data set.
Description
Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2010.
Keywords
Coral reef fishes--South Africa., Reefs--South Africa., Theses--Marine biology.