Coral dominance at the reef–sediment interface in marginal coral communities at Sodwana Bay, South Africa

Abstract

Sedimentation is an important factor that influences the composition of coral communities. The high-latitude, marginal coral community in the central reef complex at Sodwana Bay, South Africa, is subjected to sedimentation at the reef–sediment interface. A lens of bioclastic sediment surrounds the sandstone reefs in the area and acts as a scouring and smothering agent. This affects the composition of the subcommunity on the reef margin at the reef–sediment interface. The interface was studied on two reefs in the complex and their subcommunities did not differ. Alcyoniidae and Scleractinia (34.4% and 34.4% cover, respectively) are the dominant taxa in the reef–sediment subcommunity, which includes genera such as Sinularia, Lobophytum, Sarcophyton, Montipora, Favia and Astreopora (in decreasing order of abundance). Sediment-tolerant species are prevalent, the Alcyoniidae being the most prominent and tolerant by virtue of their morphology. Corals in this environment are generally flat and fairly rigid colonies of Lobophytum and Sinularia spp. (14% and 10% cover, respectively), some with lobes to channel the movement of surge-driven sediment, or are erect, soft and pliable forms such as Sarcophyton spp. (10% cover) that easily shed sediment. Their dominance in this constantly disturbed environment may also be attributable to the low mortality, slow growth and overall persistence of the Alcyoniidae described in the literature.