Abstract
Intertidal corals have been under-studied yet they provide scope for understanding adaptation and acclimatisation of corals to marginal conditions. Corals in intertidal rock pools along the east coast of South Africa withstand large temperature fluctuations, and marginal conditions for survival and growth. Four sites along the KwaZulu-Natal (KZN) coastline were sampled to determine latitudinal differences in coral communities, from 27°S to 31°S. Water temperature of rock pools at each site was monitored to see if temperature determined coral diversity in intertidal pools. Sixteen coral species were present in rock pools overall. Each of three sites in northern and central KZN hosted 12 coral taxa whereas only six taxa occurred at the most southern site. Anomastrea irregularis was the most abundant species at all sites, followed by Pocillopora verrucosa and P. damicornis. Unexpectedly, rock pool temperatures did not show a trend with latitude and thus cannot explain this decline in coral diversity. Temperatures in isolated rock pools showed large summer day time fluctuations of more than 10 °C at spring tide. However, temperatures drop substantially at high tide, lowering the mean rock pool temperature and possibly allowing these coral communities to persist in the marginal conditions of rock pools in South Africa.
Highlights
Intertidal corals have been under-studied yet they provide scope for understanding adaptation and acclimatisation of corals to marginal conditions
Eight scleractinian coral families occurred in the intertidal zone along the KZN coast with a total of 16 species (Table 2)
Temperature data were collected from 1 rock pool per site
Summary
Study site This study was conducted on the east coast of South Africa, in the KwaZulu-Natal (KZN) province (Fig. 1). Wave cut rocky platforms are horizontally-orientated rock surfaces, created by the erosion by waves along a relatively high energy coastline, while exposed rocky headlands are more verticallyoriented rock surfaces, an extension from the land [22] Despite these differences, the rock pools at each of our study sites occurred at near-horizontal surfaces between the high- and low-tide marks. Rock pools of similar size and depth were chosen, but it was impossible to avoid some variation among sites, in the case of Munster where pools were smaller than at the other sites (Table 1) This is suitable to determine a general temperature pattern in isolated rock pools at different latitudinal positions, which is not documented along the east coast of South Africa. A Wilcoxon signed-rank test was used to compare summer temperature data between Munster and Isipingo, the only two sites where summer temperature is available
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