Mesophotic Coral Ecosystems

Table 1. Data summary for scleractinian coral cover (per cent) at Eilat IUI reef, mean Shannon-Wiener index of diversity (H’), mean number of species per quadrat (#), and total number of species of all corals observed along the survey transects at 2 m, 40 m and 60 m. The survey includes three transects of 10 quadrats at each depth, with a total of 30 m 2 per depth (Eyal 2012).

Depth (m) Cover (%) Data summary for scleractinian corals at Eilat reef Diversity ( H´)

Mean per quadrat (#)

Mean per quadrat (SD)

Total no. of species

2

23.95

1.00

3.714

1.329

10

40

34.23

2.33

8.375

2.918

25

60

33.04

1.83

6.121

1.728

20

The towns of Aqaba and Eilat, located on the northernmost coast of the Gulf, are both large population centers with significant infrastructure development. The 14 km long shallow reef in Eilat was once a flourishing natural ecosystem, but in the last 40 years has been increasingly impacted by human activities (Loya 1975, 1976a, 2004, 2007, Walker and Ormond 2003). Extensive parts of the reef have been destroyed as a result of multiple factors, including inexperienced divers (Walker and Ormond 2003), sewage spillages, oil spills (Loya and Rinkevich 1980) and natural disturbances, such as extreme low tides (Loya 1972, 1976a) and severe southern storms (Eyal et al. 2011, NMP 2013). The shallow-water corals do not generally experience bleaching — although it has been hypothesized that they have been genetically selected to tolerate periods of elevated water temperature (Fine et al. 2013), new coral diseases have been reported (Rosenberg and

Ben-Haim 2002). In contrast, some of the mesophotic corals have been observed to suffer from partial bleaching during the summer, followed by recovery in the autumn (Nir et al. 2014). Bleaching is most pronounced on the lower edge of the reef slope between 40 and 63 m. It has been suggested that temperature alone is not responsible for the bleaching. Instead it may be due to a complex seasonal acclimatization regime that results in an oscillation in the mesophotic coral- algae relationship frommutualistic in the summer to parasitic in the winter (Nir et al. 2014). Currently, Eilat’s reefs are continuouslymonitored by the Israel National Monitoring Program at the Gulf of Eilat. Gradual improvement in reef healthhas been recorded in some shallow- water locations, but there is still little information on MCEs (NMP 2013).

MESOPHOTIC CORAL ECOSYSTEMS – A LIFEBOAT FOR CORAL REEFS? 30