Coral bleaching a nemesis for the Andaman reefs: Building an improved conservation paradigm
Highlights
► Coral bleaching is a major threat to Indian coastal biodiversity and economics. ► We found severe degradation of coral reefs in the Andaman Islands. ► Reef conservation is gaining impetus in India but not substantial enough. ► This paper presents various strategies to protect the coral reefs. ► Some of these approaches are novel to India and other developing countries.
Introduction
Coral reefs constitute an integral element of India's marine environment and play a key role in its coastal biodiversity dynamics. The vast Indian coastline over 8000 km long with an Exclusive Economic Zone (EEZ) of 2.02 million sq km consists of four major coral reef zones – Gulf of Kachchh, Lakshadweep, Gulf of Mannar and the Andaman–Nicobar Islands (Venkataraman and Wafar, 2005). The total area of coral reefs in India is estimated to be 2374.9 km2 with about 959.3 km2 occurring in the Andaman and Nicobar Islands (Jha et al., 2011). Among all the Indian reef zones, Andaman and Nicobar are arguably bestowed with the richest coral diversity. The Andamans are mainly dominated not only by fringing reefs but also possess some good barrier reefs (Muley et al., 2000).
The survey conducted by the United Nations Development Program (UNDP) team recorded a total of 197 stony coral species from the Andaman group of islands (Saxena et al., 2008; Turner et al., 2001). This contradicted the earlier reports of 135 species belonging to 59 genera (Pillai, 1983) and 179 species pertaining to 61 genera (Tikedar et al., 1986) from the Andaman and Nicobar Islands in total. As per the UNDP estimation, 234 stony coral species exist in the Andamans. Another team has reported a total of 177 species of hard corals from the Andaman and Nicobar Islands assigned to 57 genera (Venkataraman et al., 2003). The latest survey by a team of Zoological Survey of India has reported 418 species of corals from the Andaman and Nicobar Islands followed by a record of 44 species of mushroom corals (Ramakrishna et al., 2010a,b).
Coral reefs, popularly termed as earth's marine rainforests, are highly productive ecosystems with annual gross production rates in the range of 2000–5000 g cm−2 obtained through efficient retention and recycling of nutrients (Mann, 1982). Lately, indiscriminate exploitation and detrimental intervention on coral reefs by man has brought them on the verge of attaining the status of highly threatened global ecosystems (Hoegh-Guldberg, 2004; Pandolfi et al., 2003). Coral reef communities across the world are under increasing pressure from a multitude of environmental as well as anthropogenic impacts (Lesser, 2004). These include increased sediment and nutrient discharges (De'ath and Fabricius, 2010; Dikou and van Woesik, 2006), overfishing (Duvly et al., 2004; Jackson et al., 2001), coral diseases (Green and Bruckner, 2000; Lesser et al., 2007; Richardson, 1998) and coral bleaching (Baker et al., 2008).
Various physiological, biological, ecological and anthropological factors have been found to be accountable for bleaching events ultimately leading to mass coral mortality. The causal factors act both singularly as well as in tandem to drive widespread ecosystem alterations (Gardner et al., 2003; Wilson et al., 2006). Mostly it is the synergy of all these negative impacts that triggers the progressive collapse of the coral reef ecosystems irrespective of their geographic position and operating environmental dynamics in the surroundings.
Corals are indeed very sensitive to temperature fluctuations of even as low as 1–2 °C rise that can result in wide-scale bleaching and implies that corals live extremely close to their thermal limits (Hoegh-Guldberg and Smith, 1989; James and Crabbe, 2008). A number of assessments demonstrating varying levels of bleaching and mortality with regard to the coral reefs has been presented of late. Approximately 80% of the coral cover has been lost in the Caribbeans since the 1970s (Gardner et al., 2003) while the coral cover on reefs across the Indo-Pacific zone is declining at the rate of 1–2% per annum (Baker et al., 2008; Bruno and Selig, 2007; Scopélitis et al., 2009). These changes have expectedly raised concern about deteriorating coral reef health as well as degree of reef resilience (Bellwood et al., 2004). These concerns are amplified by near-future environmental change projections of rising global sea levels, sea surface temperatures and ocean acidification (Kleypas et al., 2001). Our study indicates that the situation in Andamans is worse than what has been stated in the previous assessments (Krishnan et al., 2011; Vivekanandan et al., 2009). Rise in sea surface temperature and anthropogenic impacts are the primary factors active in the Andaman Islands.
Section snippets
Study site
The Andaman and Nicobar Group of islands is located in the south-east of the Bay of Bengal, between 6°–14°N latitude and 91°–94°E longitude. This Union Territory of India is 150 km north of Aceh, Indonesia and separated from Thailand and Burma by the Andaman Sea. The Andamans are separated from the Nicobars by the Ten Degree Channel. The orientation of the chain of islands is north–south. A total of 572 islands constitute the Andaman–Nicobar, of which only 38 are inhabited. For conducting the
Materials and methods
In this study, the magnitude of coral bleaching was estimated using the Line Intercept Transect (LIT) method (English et al., 1997). In addition, visual inspection from a low draft glass bottom boat was also used to assess the status and distribution of coral reefs (Table 1). Extensive studies on the taxonomic and ecological characteristics were carried out during low tide conditions. To estimate the percentage cover of corals at each site, the LIT was applied using five transects (Table 2).
Results
The coral cover estimated at the study sites was analyzed separately to determine the extent of bleaching and coral health. It was found that the percentage of bleached corals (partially bleached, fully bleached but not dead and dead corals) as a component of total estimated data (excluding sand and algae) was maximum at Ross Island (88.7) followed by Havelock (86.2), North Bay (84.1), Chidiyatapu (82.4), Neil (77.0) and Jolly Buoy (43.3). The percentage of healthy corals was maximum at the
Threats to the coral reefs
The last few decades have witnessed a voluminous demand for industrial development along the coastlines of India (Kaplinsky, 1997; Khemani et al., 1994; Santhiya et al., 2011). This cycle has accelerated the stress on coastal ecosystems in terms of population concentration, development of ports, waste effluent and sewage discharges, increased recreational activities like fishing, diving etc. All four reef zones of India are under the impact of coral bleaching (Fig. 1). Terrestrial activities of
Conclusion
An overview of the coral reef status in this case study reveals that they are under serious threat and undergoing degradation due to persistent anthropogenic activities and climate change. This impact is visibly higher for coral reefs nearer population centers. Better status of coral reefs in the Jolly Buoy proves that with improved efforts for conservation, excellent results can be obtained in the near future. Natural disturbances (e.g., earthquakes and ensuing tsunamis, cyclones) are
Acknowledgment
This study was funded by the Council of Scientific and Industrial Research, India (Grant No. 09/528(0016)/2009-EMR-I). We wish to thank Dr. N.C. Mehrotra, the director of our institute for his support toward the coral reef research being carried out at the Andaman Islands. An earlier version of the manuscript benefited greatly from the comments of Dr. John A. Madsen and Dr. Simon Thrush. The authors would also like to acknowledge Dr. Samir Sarkar for his help and useful inputs during the field
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