Biogeographic patterns on shallow subtidal reefs in the western Indian Ocean |
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Authors: | S N Porter G M Branch K J Sink |
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Institution: | 1. Marine Research Institute, Zoology Department, University of Cape Town, Rondebosch, 7701, South Africa 3. Anchor Environmental Consultants, 8 Steenberg House, Silverwood Close, Tokai, 7945, South Africa 2. South African National Biodiversity Institute, Private Bag X7, Claremont, 7735, South Africa
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Abstract: | To resolve biogeographic limits and patterns on the east coast of Africa, the presence/absence and quantitative biomass data were collected from 55 shallow subtidal reefs along 4,800 km of coastline (5.2°–31.1°S). Multivariate analysis of distributions, trophic structure and biomass revealed two distinct marine provinces, the Tropical Indo-West Pacific and Subtropical Natal, with a transitional overlap (of ca. 120 km) located between Leven Point and Kosi Mouth on north-east South Africa. This region of overlap was one of three bioregions revealed by post hoc analyses. Biomass was unexpectedly highest in the tropics. ‘Auto-heterotrophs’ (species with autotrophic symbionts such as corals and clams), deposit feeders and grazers contributed significantly more biomass to the Tropical Indo-West Pacific Bioregion, whereas filter feeders dominated the Subtropical Natal Bioregion. ‘Auto-heterotrophs’ declined with latitude while filter feeders increased; soft corals made a defining contribution in the overlap bioregion. Possible underlying causes of these patterns include productivity, nutrient levels, riverine input, light penetration and temperature. |
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