Coral community structure and risk assessment of high-latitude reefs at Sodwana Bay, South Africa

Abstract

The importance of studying coral communities at different spatial scales is acknowledged in a growing volume of scientific literature, and principles of landscape ecology were thus used to elucidate the patterns in coral community structure on the highlatitude reefs in South Africa. These reefs are at the southernmost distribution of this fauna in Africa, are surprisingly species rich, and represent a biodiversity peak in this fauna south of the equator, regardless of the marginal nature of the environment. Coral community patterns were identified on and between the reefs at Sodwana Bay, justifying the grouping of reef areas in distinct zones. A number of landscape components were identified, ranging from the entire reef complex (10 km scale), individual reefs (1 km scales) and reef zones, to components that were separated using multivariate statistical analysis of transect data. These components transcended spatial similarities, e.g. the fore-reef on Five-mile Reef was not similar to the fore-reef on Seven-mile Reef, but was rather grouped with the reef flat on Two-mile Reef. This information was ''translated'' into an index of management intervention, based on risk assessment, and was generated using parameters that measure susceptibility to crown-of-thorns feeding, bleaching, diver-related damage and swellinduced breakage. We also assessed was the time elapsed since the last major disturbance and the proximity to the only boat launch site, a proxy measure of continuous disturbance. The risk assessment suggested that conservation management is most needed in the stable and ''climax'' coral communities that are usually characterised by a near-equal mix of hard and soft corals at maximal coral species diversity.

Sublittoral seaweed communities on natural and artificial substrata in a high-latitude coral community in South Africa

“…Estimates of hard coral cover (as a percentage of total benthic cover) on Sodwana reefs vary considerably. Riegl et al (1995) and Riegl and Riegl (1996) reported values around 22.5% for Two-Mile Reef, Schleyer et al (2008) reported averages around 10-12% at Nine-Mile Reef and Celliers and Schleyer (2008) reported values of 29% for Two-Mile Reef. Our value of 48.4% is consequently very high, but similar to that of 48.8% reported for Four-Mile Reef by Celliers and Schleyer (2008).…”

“…Riegl et al (1995) and Riegl and Riegl (1996) reported values around 22.5% for Two-Mile Reef, Schleyer et al (2008) reported averages around 10-12% at Nine-Mile Reef and Celliers and Schleyer (2008) reported values of 29% for Two-Mile Reef. Our value of 48.4% is consequently very high, but similar to that of 48.8% reported for Four-Mile Reef by Celliers and Schleyer (2008). Although this might indicate that Two-Mile Reef was in good condition at the time we sampled, we suggest that such comparisons should be treated with caution, as differences between methods (point-intercept vs photographic quadrats), total area sampled and sampling site would all affect such data.…”

“…Two-Mile Reef is a highly rugose patch-reef system, with reef ridges, reef slopes and gullies (Ramsay and Mason 1990;Jordan and Samways 2001). The reef, lying 1 km offshore, is approximately 1.8 km long and 900 m wide and is always submerged (Ramsay and Mason 1990;Celliers and Schleyer 2008). The water depth on the reef varies between 6 and 10 m on its shallowest pinnacles, to 14-19 m on extensive deep subtidal reef flats and 24-27 m at the edge of the fore-reef (Celliers and Schleyer 2002).…”

“…In addition, the species composition of algal assemblages differed according to the severity of bleaching damage to the corals: species composition on severely bleached corals was in a more developed successional stage than that on less-bleached corals. The inshore, high-latitude coral communities of southern Africa suffered negligible impacts during past mass bleaching events, but the most recent bleaching in 2005 in southern Africa, when a warm-water anomaly affected much of the southern Indian Ocean, resulted in more extensive damage to coral on South African reefs (McClanahan et al 2007;Celliers and Schleyer 2008). Although some information on subtidal macroalgal turf communities in Sodwana Bay is available , there is no information on the distribution ofmacroalgal assemblages on the different types of hard substrata, including dead corals.…”

High Resolution Orthomosaics of African Coral Reefs: A Tool for Wide-Scale Benthic Monitoring

“…Outcrops are present (Figure 1b,c) and originate from fossilization of Late Pleistocene beaches and dunes [49] that form very flat structures [50]. The area is characterized by high levels of endemic species [51][52][53] with the coral cover being dominated by soft corals that are tolerant to strong wave energy and sediment resuspension [54][55][56][57]. …”