*4.1. Status of Reefs and Extent of Impacts*

Located close to the southern tip of the Indian sub-continent, Sri Lanka's coral reefs are surrounded by other well-developed reef areas in both the Western Indian Ocean and the Bay of Bengal. India has three coral reef regions, one of which, Palk Bay, lies adjacent to the present study area, on the opposite side of the Palk Strait. The others, lying much further away, are the Andaman and Nicobar Islands in the Bay of Bengal and the Lakshadweep islands located between the west coast of India and the Maldives. Further to the west lie the Maldives and the Chagos Archipelagoes [54,55]. According to Arthur [56], the reef faunas of the Gulf of Mannar and Palk Bay islands are closely related to those of other Sri Lankan coral reefs. However, the differences described here in benthic composition between islands in the Palk Bay and northern coast sites in the Palk Strait suggest that, in terms of coral cover and species present, the Palk Strait reefs may also be compared to those in the above-mentioned neighbouring regions (Figure 7).

To date, it was presumed that all the coral assemblages of Sri Lanka are less welldeveloped and diverse than those in these other regions. Due to the limited accessibility created by the civil war, previous surveys around the Jaffna Peninsula were essentially limited to confirmation of the presence of fringing coral reefs around the islands [10,27,28]. The first quantitative report was prepared only in 2005, as part of an environmental impact assessment of the Sethusamudram Ship Channel project [27]. Even then, only rapid surveys were conducted at four reef sites (Pungudutivu, Eluvaitivu, and two locations in Kankeasanthurai harbour), while two other fringing reefs, on Analaithivu and Karathivu islands, were inspected visually to assess their condition. The study reported live coral cover on the four reefs surveyed to be between 35% and 58% [24]. In contrast, this present study found that live coral cover at the majority of sites varied between 27% and 49%, with only the Point Pedro site having more than 50% live coral cover. While this difference might

relate to differences in methodology or to the present study being restricted to shallow depths, an alternative explanation is that coral cover has declined since 2005 as a result of one or more impacts.

The structure of the benthic cover at the island sites in the Palk Bay is somewhat similar to reefs in nearby regions that have been similarly subject to climate-related coral bleaching and to fishing related impacts; thus, reports of findings on the Indian reefs may provide some understanding of the impacts likely to have affected the study area [56–60]. At most sites, turf algae growing over old corals appeared to be the predominant substrate and the contribution of coral rubble to the substrate was also noticeable, suggesting that coral cover may have been higher in the past. Algal-dominated reefs are often associated with post-bleaching impacts [60,61]. A more recent study has described the extent of bleaching in the region, with bleaching being much higher in Palk Bay (71.48%) at the depth of 2–3 m than towards the Gulf of Mannar (46.04%), where the coral communities are deeper than 6 m [60]. Quantitative studies in Lakshadweep, the Gulf of Mannar, and the Andaman and Nicobar Islands have described a reduction in live coral cover and declining reef health primarily due to bleaching events from 1998 to 2015 [56,58]. More than 70% of coral cover was bleached in the Andaman Islands, Gulf of Mannar, and Lakshadweep islands during the two global bleaching events in 1998 and 2010 [60,62–68]. The bleaching event of 1998 also caused extensive coral mortality in the southern, south-western, and north-western parts of Sri Lanka [69–71], but did not affect the coral reefs in the Pigeon Island, Northern Park, and Dutch Bay areas of eastern Sri Lanka [71]. The tsunami event of December 2004 is also known to have affected the eastern and southern coral reef regions of Sri Lanka [70,71].

On the other hand, coral reefs in the Andaman and Nicobar Islands, Lakshadweep, Gulf of Mannar, Chagos Archipelago, and Maldives have shown considerable recovery following past bleaching events [57–59,64–68]. Post-bleaching monitoring observations in Lakshadweep showed a reduction in the dead coral-algal substrate, coral recruitment, and an increase in live coral cover supporting a phase shift back from algal-dominated reefs to live coral-dominated substrates [58,61]. A similar scenario might have been experienced in the present study area by the Palk Bay islands, resulting in the observed high percentage cover of standing dead coral with turf algae and of coral rubble. In addition, another recent report on the biodiversity of northern Sri Lanka indicates a similar pattern of coral benthic composition on many of the islands in Palk Bay, including Punkudutivu [24].

However, it may be suggested that the recovery of corals in the Gulf of Mannar and Palk Bay has been severely hindered by illegal fishing by vessels. These vessels operate even in the shallowest areas, stirring up the bottom and causing sedimentation [58,61,69]; they are also involved in bottom trawling, which overturns corals and causes direct damage [24–26,72]. The area is also subject to illegal fishing practices such as blast fishing [72]. More generally, the inshore reefs, especially along the northern coast of JP, are subject to considerable fishing pressure, with 21 fish landing sites present within 48 km of coastline, and a higher number of fishing vessels operating than anywhere else in the nation [73]. These reefs have also been subject to other impacts, including increased terrestrial runoff and direct damage and sedimentation resulting from dredging and the creation of boat channels at Pungudutivu, Kayts, Point Pedro, and Valithoondal. Given the scarcity of available data, further detailed research will be required to elucidate the interacting effects of environmental conditions, seasonal variation, local anthropogenic pressure, and global climate change on the community structure of these reefs.
