*3.2. Diversity, Taxonomic Composition, and Distribution of Coral Species*

The taxonomic study across the eight reef areas surveyed revealed a total of 113 scleractinian coral species, from 39 genera and 16 families, together with seven soft coral genera (Table 1). Among these, 36 species of hard corals appear to be new records for Sri Lanka (Table 2), including species of the genera *Oulastrea, Coeloeris,* and *Siderastrea*, although all have been recorded in other parts of the Central Indian Ocean. The full species list (Table 1) includes 39 members of the family Merulinidae (44% of the total), 28 species of Acroporidae (32%), and 13 species of Poritidae (15%). The predominant genera present were *Acropora* (17 spp.), *Dipsastraea* (10), *Porites* (7), *Favites* (6), *Montipora* (6), *Goniopora* (6), *Turbinaria* (5), and *Platygyra* (5) (Supplementary Table S2).

**Table 2.** Numbers of families, genera, and species of scleractinian corals recorded in each of the eight reef areas studied around the Jaffna Peninsula, Sri Lanka.


The numbers of genera and species recorded differed between the study sites (Table 2). On the northern coast, massive coral growth forms were predominant and the principal genera present were *Dipsastraea* (6 spp.), *Porites* (6), *Montipora* (6), *Favites* (5), *Platygyra* (4), *Goniastrea* (3), and *Symphyllia* (3). Encrusting growth forms of the genera *Symphyllia, Lobophyllia* and *Acanthastrea* were also more common on the northern coast. In contrast, around the island sites, tabulate and branching *Acropora*, foliose *Montipora*, massive *Porites,* and smaller *Goniastrea* predominated, with branching and tabulate *Acropora* and foliose growth forms occupying large areas. The Pungudutivu and Kayts island sites, in particular, were dominated by branching and tabulate *Acropora,* followed in substrate cover by *Porites*. The genus *Echinopora* was observed at Point Pedro, Thondaimanaru, Pungudutivu, and Kayts Islands. Only a single colony of *Pocillopora verrucosa* was documented, being at Point Pedro, while scattered *Pocillopora damicornis* were recorded on the Inabarsitty and Thondaimanru reefs. The newly recorded species *Acropora gemmifera* was found at all the study sites, but *Acropora aspera*, *Acropora digitifera, Montipora flabellata,* and *Echinopora gemmacea* were uncommon, with only one colony recorded at any site.

Soft coral colonies representing the genera *Capnella, Cladiella, Clavalaria, Lobophyton, Subergorgia,* and *Sarcophyton* (Supplementary Table S1) were uncommon and made only a minor contribution (2–4%) to substrate cover, but they were found on the northern coast and on the islands of Karainagar and Delft.

A comparison of the number of species present at different sites showed that the northern coastal sites had higher richness and diversity than the island sites (Tables 3 and 4). Calculation of Shannon's diversity and evenness indices suggested that all the reefs, excluding Pungudutivu, had comparable diversity and evenness values (H' ≥ 2.5; E ≥ 0.9), with a low dominance index (D ≤ 0.1). The Point Pedro reef front had nearly 50 hard coral species, followed by Thondaimanaru with 44 hard coral species (Table 3), but the Shannon–Weiner diversity index at Thondaimanaru was higher (H' = 3.020) than that at Point Pedro (H' = 2.927) (Table 4).

The relationships between mean values of live coral cover and the different diversity indices (Shannon's Diversity Index—H', Simpson's Dominance Index—D, and Evenness index—E) were investigated separately for each of the two parts of the study area, i.e., the island sites (Karainagar, Pungudutivu, Kayts, and Delft) and the northern coastline (Point Pedro, Inbarsitty, Thondaimanaru, Valithoondal). The relationship between these indices on the northern coast and on the island sites was further analysed with a Pearson correlation. On the northern coast, there was a moderate positive relationship between diversity and live coral cover (Pearson correlation: r = 0.64, *p* > 0.05). In contrast, among the island sites, there was a strong negative correlation between both diversity index (Pearson correlation: r = −0.96, *p* < 0.05) and evenness (Pearson correlation: r = −0.98, *p* < 0.05) on the one hand and live coral cover on the other. Similarly, there was a negative correlation (Pearson correlation: r = −0.51, *p* > 0.05) between the dominance index and mean live coral cover on the northern coast, but a strong positive correlation (Pearson correlation: r = 0.96, *p* < 0.05) between these variables among the island sites (Supplementary Figure S2).




**Table 4.** The richness and values of diversity and evenness indices for hard corals at each of the study sites of the Jaffna Peninsula.
