*4.2. Coral Species Diversity*

This study has significantly improved knowledge of the coral species present in the study area. Previously, no comprehensive coral inventory had been produced for these reefs [11,20,21,27,28], which now appear to perhaps be some of the most biodiverse in Sri Lanka.

Ridley (1883) made the first note recording 49 coral species in Ceylon (Sri Lanka), his specimens being deposited in the British Museum [12]. Subsequent studies on coral species and their distribution were mostly undertaken in the more southern parts of Sri Lanka at sites including Galle, Hikkaduwa, the Kalpitiya Peninsula, Unawantuna, Weligama, Polhena, Tangalle, the Great and Little Basses, and Trincomalee [9–11,19–21,28]. In comparison, the coral reefs of northern Sri Lanka have been under-studied, except for those in the Gulf of Mannar (in north-west Sri Lanka). There was, however, some preliminary information on aspects of the coral fauna of the Jaffna area [24,27]. Initial rapid surveys by Rajasuriya [27] noted at least 43 species of hard corals belonging to 20 genera. He commented that the coral reefs on the north coast and around Pungudutivu Island were more diverse than those at other study sites in the area. In contrast, the present study recorded a total of 113 hard coral species belonging to 40 genera from just eight reef areas, with the highest number of species being recorded at Point Pedro reef front (50 spp.), followed by Thondaimanaru (44 spp.) (Table 2).

Several species recorded in the present study have also been found at other coral reef sites in Sri Lanka [9], while many were listed in the corals of India [74–77]. Thus, in terms of coral species diversity, the reefs appear more comparable to other Indian territorial reefs (Figure 7). According to Raghuraman et al., 2012 [76], the various reef areas of India support a total of 478 species, representing 19 families and 89 genera. Considering the coral species recorded, the closest faunistic relationship of the Jaffna Peninsula reefs is to the reefs of the Andaman and Nicobar Islands [12,16]. However, fewer species (133) were reported here than in the Andaman Islands, where around 400 species of corals have been recorded. Coral species diversity was also similar to the Gulf of Mannar, further to the west, which has about 100 species [75]. Of the 36 coral species reported here as new records for Sri Lanka, most appear to be widely but patchily distributed across the central Indian Ocean and the Arabian Sea (Table 3) [75], with the largest proportions of these also recorded from the Andaman and Nicobar Islands (23 spp.), the Arabian Sea (21 spp.), and the Central Indian Ocean (30 spp.) [61,74–76].

**Figure 7.** Comparison of the numbers of scleractinian corals recorded in different parts of India and Sri Lanka in relation to the Jaffna Peninsula and its islands. Pink colouring indicates the location of reef areas; the pink circle in the centre indicates the location of the present study areas at the northern end of Sri Lanka) [24,62,75,77].

Since the ability of corals to survive and recover after a bleaching event varies between species, greater species richness may endow a habitat with greater community tolerance and a greater ability to adapt to sea surface temperature changes [78–81]. At the same time, species abundance and overall coral cover will also be influenced by natural environmental factors such as wave action, salinity, exposure to light, and sediment loading [82]. In the present study, thermally tolerant encrusting and massive coral growth forms such as *Porites, Favites, Goniastrea,* and *Dipsastraea* were found to have survived to a greater extent than branching species of the genera *Acropora, Pocillopora,* and *Stylophora*, which are more susceptible to thermal events in many Indo-Pacific regions [78,79]. Nevertheless, large colonies of tabulate and branching *Acropora* and tiered plates of *Echinopora* and *Montipora* dominated the islands, while massive coral colonies dominated the northern coast. Similar patterns of coral distribution have been described in earlier studies [24], with large domes of stress-tolerant *Dipsastraea, Favites, Goniastrea, Platygyra* and *Porites* [79,80,83] occupying shallow reef flats down to 6 m depth. Notably, there were only a few small colonies of *Pocillopora* and *Stylophora* observed during the present study; this may result from their susceptibility to past bleaching events.

Of the species recorded in the present study, three are listed as "vulnerable" by the International Union for the Conservation of Nature (IUCN): *Acropora aspera, Acropora specifera,* and *Acropora hemprichii.* These were found at the Punkudutivu, Kayts, and Karainagar island sites, respectively. In addition, "threatened" species of *Montipora flabellata, Turbinaria frondens, Turbinaria stellulata*, and a rare species of *Astreopora ocellata* were also recorded during this study.
