Coral Reefs 2001) 20: 244 Reef sites Acropora hyacinthus and Acropora austera dominance on a high-energy reef top at Kosi Bay, South Africa Accepted: 21 June 2001 / Published online: 24 August 2001 Ó Springer-Verlag 2001 The southernmost coral communities on the coast of East Africa are located within a northern, central and southern reef complex in northern KwaZulu-Natal, South Africa. The exposed coastline and prevailing long-shore, north-easterly and southerly to south-westerly winds in the region give rise to swells that occasionally exceed 6 m in height data from South African Data Centre for Oceanography). The South African coral communities thus consist of marginal, high- latitude species adapted to high-energy swells and surges. Soft corals of the family Alcyoniidae are most frequently dominant on the subtidal reef tops Riegl et al. 1995; Schleyer 1999) and scleractinian corals, particularly the ge- nus Acropora, were previously thought to be more abundant only on the deeper >20 m) reefs Riegl et al. 1995). The latter authors argued that these corals would encounter excessive turbulence in the high surge on shallower reefs due to their shape, resulting in structural failure. However, 25 video transects of representative areas on Kosi Reef in the northern reef complex yielded 6 transects with Acropora cover exceeding 30% in shallow areas 10±15 m). The spe- cies contributing most towards this predominance of Acro- pora on the reef top were A. austera and A. hyacinthus. Their distribution on Kosi Reef is congruent with their habitat preference described by Veron and Wallace 1984). The latter authors concluded that A. austera and A. hya- cinthus occupied a wide range of habitats, but were most abundant in shallower areas exposed to some wave action. Colonies of A. austera on the shallow, turbulent reef top at Kosi Bay were low, sprawling and arborescent, with ex- ceptionally thick branches and short branchlets Fig. 1a; scale bar 10 cm). The Acropora hyacinthus colonies were thick and heavily calci®ed, with their branches fused into a solid plate at the centre Fig. 1b; scale bar 10 cm). The heavy calci®cation and dominance of these Acropora spp. on the high-energy reef-top environment created a diversity of niche space populated by a wide range of ®shes personal observation). This abundance of the species in question is anomalous in South Africa as they are not found to any great extent on any of the other reefs in the central and northern reef complexes at depths shallower than 20 m. They are found to a certain degree on shallow reefs in southern Mozambique unpublished data). However, the local abundance of A. austera and A. hyacinthus at the Fig. 1 limits of their distribution on Kosi Reef is fairly unique and probably attributable to their opportunistic success under incidental, amenable conditions. The latter must at least partially comprise a measure of reduction of the turbulence that limits coral development on the southern reef tops to soft corals. A block of bare, shallower 6 m) reef immediately to the north Schleyer and Celliers 2000) must aord the Acropora-dominated areas on Kosi Reef some protection from wind-driven swells from that direction. A slight attenuation of the force of southern storms by virtue of a greater distance from their origin constitutes another likelihood. Acknowledgements We gratefully acknowledge logistical and ®nancial support for this work by South African Network for Coastal and Oceanic Research, National Research Foundation, Marine Living Resources Fund, South African Association for Marine Biological Re- search, Mazda Wildlife Fund, BP Southern Africa and KwaZulu-Natal Wildlife. References Riegl B, Schleyer MH, Cook PJ, Branch GM 1995) Structure of Africa's southernmost coral communities. Bull Mar Sci 56:676±691 Schleyer MH 1999) A synthesis of KwaZulu-Natal coral research. Spec Publ 5. Oceanographic Research Institute, Durban Schleyer MH, Celliers L 2000) The major reef complex at Kosi Bay in northern Maputaland, KwaZulu-Natal, South Africa: bathymetry, reef map, biodiversity and recommended zonation for use. South African Association for Marine Biological Research, Rep 192, Durban, pp 1±28 Veron JEN, Wallace CC 1984) Scleractinia of eastern Australia, part V, Family Acroporidae. Australian Institute of Marine Science Monograph Series vol 6. Australian Institute of Marine Science, Australian National University Press, Canberra, pp 1±485 L. Celliers &) á M.H. Schleyer Oceanographic Research Institute, P.O. Box 10712, Marine Parade, 4056 Durban, South Africa E-mail: seaworld@dbn.lia.net; Fax: +27-31-3372132