Management of Coral Reefs in Gulf of Mannar using Remote Sensing and GIS Techniques – with Reference to Coastal Geomorphology and Land Use M. Thanilachalam and S. Ramachandran Institute for Ocean Management Anna University Chennai-600 025 Tel: 2200158, Fax: 2200159 Email: aisuwariyaa@yahoo.com Abstract The coral reefs characterise an ecosystem of high biological diversity, having the greatest number of species of any marine ecosystem. Livelihood of many millions of people is dependent on this unique ecosystem as a considerable proportion of their food and earning is from the productivity of coral reef. Coral reefs are considered as one of the most important critical resources for various ecological, environmental and socio-economic reasons. Coral reefs act as a barrier against wave action along coastal areas thus preventing coastal erosion. In addition, coral reefs protect mangroves and seagrass beds in certain areas, which are the breeding and nursing grounds of various economically important fauna. Coral reefs are also important breeding, spawing, nesting, and feeding areas for many economically important varieties of fishes and other marine organisms. As a result of the increasing human population along the coastal area, anthropogenic impacts on the coastal zone have become severe over the past few decades. Coral ecosystem also face many threats, of which some are of natural origin like storms and waves particularly tropical storms and cyclones that cause major intermittent damage to reefs. The majority of damage to coral reefs around the world has been through direct anthropogenic stress. In Gulf of Mannar, the coral reefs have been used as a source of calcium carbonate and building blocks. In general, coral reefs in Gulf of Mannar can be categorised as “degrading”, and hence, monitoring and management of these valuable marine resources are of prime importance. In this contest Survey of India Topographic Sheet (1969), Naval Hydrographic Chart (1975) IRS LISS-II (1988), IRS LISS-III (1998) satellite data and ARC-INFO and ARC-VIEW GIS software were used for coastal geomorphology, seafloor, shoreline, coastal land use/land cover and coral reef mapping from Gulf of Mannar. The current status of coral reef, changes and important coastal problems (coastal geomorphological and land use/land cover changes) for coral reef degradation of Gulf of Mannar are identified. 1. Introduction Coral reef system as also the ecosystem of the tropical rain forest, are the most matured marine ecosystems of our planet. They play an important role in global biochemical processes and in the reproduction of food resources in the tropical regions. Coral reefs act as a barrier against wave action along coastal areas thus preventing coastal erosion. In addition, coral reefs protect mangroves and seagrass beds in certain areas, which are the breeding and nursing grounds of various economically important fauna. Coral reefs are also important breeding, spawing, nesting, and feeding areas for many economically important varieties of fishes and other marine organisms. The people living along the coast obtain a considerable proportion of their food and earnings from the productivity of coral reefs. Coral reef ecosystems are very sensitive to external impacts both natural and manmade, which violate their homeostasis (Sorokin 1992). The majority of damage to coral reefs around the world has been through direct anthropogenic stress (Grigg and Dollar 1990). According to Bryant et.al (1998), 57% of the world’s coral reefs are potentially threated by human activity such as coastal development, destructive fishing, over exploitation, marine pollution, runoff from deforestation and toxic discharge from industrial and agricultural chemicals. As global pressures on coral reefs and related ecosystems grow with developing economies and increasing coastal populations, the need for careful monitoring , planning and management become essential (Knight et.al 1997). Gulf of Mannar, extends from Tuticorin to Rameswaram Island in the SW-NE direction, lies between 78º 5’ & 79º30’ E longitudes and 8º47’ & 9º15’ N latitudes, to a length of about 140 km. There are 21low islands (Figure 1) situated at an average distance of about 8km from the coast and running almost parallel to the coastline. These islands are broadly grouped into Tuticforin, Vembar, Keelakkarai and Mandapam groups. These areas are endowed with a combination of ecosystems including mangroves, seagrass, seaweeds and corals reefs. Different types of reef formations have also been observed along the periphery of the islands viz. fringing reef, patch reef and coral pinnacles.  Figure 1 Location map of the study area (Gulf of Mannar) In South India the coral reefs have been used as a source of calcium carbonate, building blocks and rubble for construction of roads (Mahadevan and Nayar 1972). Blasting and dredging activities result in high sedimentation on the coral reef of Gulf of Mannar there by leading to its degradation. The coral reefs of Tuticorin group of Islands in Gulf of Mannar have been damaged due to the discharge of effluents from petrochemical and other industries along the coast, and fly ash discharges from thermal plants (Ramanujam and Mukesh 1998). In general, coral reefs in Gulf of Mannar can be categorised as “degrading”, and hence, monitoring and management of these valuable marine resources are of prime importance. To study coral reefs area effectively and to monitor changes over timw, accurate, rapid and cost-effective mapping techniques are required. Satellite remote sensing is widely used as a tool in many parts of the world for the management of resources and activities within the continental shelf containing reefs. Preliminary studies carried out in India by Space Application Center (SAC) Ahmedabad, have proved the importance of remote sensing data in mapping and monitoring of the coral reef (Muley et al. 1986; Nayak et al. 1987). Anjali Bahuguna and Nayak (1998) have mapped the coral reefs of Gulf of Kachchh, Lakshadweep, Palk Bay, Gulf of Mannar and Andaman and Nicobar Islands using IRS and SPOT satellite data. Mumby et al (1998) used digital airborne sensor of Landsat MSS, Landsat TM, SPOT XS, and SPOT PAN and merged Landsat TM/SPOT PAN for mapping the coral reef in Turks and Caicos Islands they also studied coral reefs in situ by visual technique.
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