India has a long coastline of over 8000 km with associated continental shelf of 0.5 million km2 and an Exclusive Economic Zone of 2.02 million km2. The coastal zone of the country with its wetlands, lagoons, mangroves, sea-grass beds, coral reefs and shallow bays, creeks and estuaries is rich in natural resources. Unfortunately, much of this wealth is often exploited in an indiscriminate or ill-planned manner resulting in rapid resource depletion and irreversible environmental degradation. Major driving forces for coastal degradation include (a) high rate of growth in population leading to reclamation of coastal areas and release of wastes, (b) over-fishing due to lack of alternative livelihoods, (c) large commercial enterprises aiming at quick profit at the cost of sustainability and their insensitivity to the interests of local inhabitants, (d) ignorance about management of resource sustainability among stake holders and policy makers, (e) lack of understanding of environmental significance and importance of coastal habitats, and (f) inadequate enforcement of environmental rules and regulations.
The present paper examines the trends that have emerged concerning the status of the nearshore ecology of India in the context of development activities. Many scientific programmes of the National Institute of Oceanography are focussed on marine ecology along the Indian coast and the results emerging from these studies and those by other institutions in the Country are used in the assessment.
The mangroves are wide spread along the Indian coast. Gangetic Sundarbans occupying an area of 2067 km2 is the largest single block formation of mangroves in the world annually yielding 30,000 t of fish, crab and prawn. Mangroves of the A&N Islands are the second largest in India. The other prominent mangrove formations are in the deltaic areas of Mahanadi, Godavari, Krishna and Pichavaram and Puthupet on the East coast. Mangroves, though to a lesser extent, also occur along the West coast in the states of Gujarat, Maharashtra, Goa, Karnatata and Kerala. The total area under mangroves along the Indian coast is estimated at 4460 km2 (Nayak 1998).
Overexploitation and unsustainable demand has resulted in considerable degradation of mangrove areas though exact estimates are not available. Mangrove formations along the Gujarat coast have declined from 165.2 km2 in 1992 to 128.9 km2 in 1998 when mangroves of the Kachchh District are excluded. Significant improvement from 601.8 km2 to 938 km2 over the same period has been reported in the mangrove formations of the Kachchh District probably because these areas are remote and not easily accessible (Bahuguna et al 1998).
The major coral formations are around the Lakshadweep (816 km2) and A&N Islands (960 km2) as well as in the Gulf of Mannar (94 km2) and the Gulf of Kachchh (460 km2). Many of these areas are under anthropogenic pressure due to mining, dredging, fishing, coral collection and recreational activities. The coral reefs of the Gulf of Kachchh have been degraded to a considerable extent with the deposition of mud over reef. Localised reef areas of the A&N Islands also have mud deposits. These deposits of mud on reefs are as a result of mangrove deforestation. A study conducted in the Lakshadweep and Andaman Islands as well as the Gulf of Kachchh indicates that disease, predation and stress are the major factors of coral mortality (Ravindran et al 1999).
The progress and the problems of marine fishery of India have been reviewed by Devraj and Vivekanandan (1999). The marine fish production in India is exclusively from the capture fisheries, barring an annual production of about 0.7 million t of brakishwater prawns through aquaculture. However, the production from inshore waters (< 50 m depth) has reached the catchable potential (2.2 million t/y) and scope for further increase in production from nearshore waters is limited. Inappropriate exploitation patterns of concentrating 80% of the total fishery effort in the nearshore areas and over-dependence on trawlers is feared to have become counter productive. The catch rate of fishing vessels in several fishing centres is on the decline leading to an increase in competition and, often, conflicts between different fishing fleets.
Among other factors, the trawlers are also responsible for declining population of the Olive Ridley sea turtles, an endangered species, which nest along the East coast of India, due to incidental capture of adults in fishing nets (Pandav et al 1998). The rookery at Gahirmatha in Orissa has been the largest in the world with annual nesting of 0.1 to 0.5 million turtles
With active encouragement by the government, shrimp culture boom was witnessed during early 1990s. Unfortunately, the developments were unplanned and basic norms with regards to water treatment, use of antibiotics, seed quality, pond fertilisation, effluent disposal practices etc were flouted. The cumulative effect of this negligence was the severe outbreak of white spot disease in 1995 that wiped out the crop in majority of aquaculture farms. Since then though the virulence of the virus seems to have declined, sporadic mass mortalities occur locally (BOBP 1998).
Indiscriminate releases of untreated or partially treated wastes without considering the assimilative capacity of the waste receiving water body have resulted in pockets of polluted environs with depleted coastal resources, public health risks and loss of biodiversity. Over 300 million people living in the coastal zone of India are considered to generate 1.11 x 1010 m3 of sewage annually, a considerable fraction; particularly from coastal cities and towns where sewage collection network exists, enters the marine waters (Zingde 1999).
There is a high concentration of large and medium industries within the narrow coastal belt of 25 km width than the rest of the country. These industries are estimated to generate 1.35 million m3/d of liquid effluent and about 34,500 t/d of solid waste. The West coast of India is more industrialised than the East coast with Maharashtra and Gujarat having largest concentration of industries. A 1994-95 survey (CPCB 1996) revealed that out of 308 large and medium industries in the country, 233 were located along the West coast. A major fraction of the liquid effluents is released to marine areas, presumably treated, to meet specifications of the respective state pollution control board. In addition, aquaculture farms, largely concentrated in Andhra Pradesh and Tamil Nadu, generate 2.37 million m3/d of effluent.
Much of the development along the coast has taken place several kilometers inland from the shoreline. Primary considerations for such developments in the past had been the availability of water, electricity and transport, while, environment received the lowest priority. Evidently, many industries are located near national highways and railway stations and release their effluents in nearby rivers, estuaries or creeks. Nearly 8% of industries in the country are located around Mumbai in four large industrial clusters namely, Trans Thane-Belapur belt, Kalyan-Ulhasnagar-Ambarnath belt, western bank of Thane Creek and around Patalganga and Amba Rivers. Evidently, Ulhas, Patalganga and Amba rivers as well as Thane Creek are the recipients of a variety of wastes (Zingde 1999).
On a conservative estimate the oil demand of 94 million t in 1999-2000 is projected to reach 155 million t by 2006-07. Domestic production however, was only 31.95 million t in 1999-2000 and met about 34% of the total need making it inevitable to import large volumes of oil. Despite best efforts put in so far, indigenous crude oil production is expected to be only around 58 million t on an annual basis by 2006. Hence, the wide gap between the indigenous production and demand will continue to be met through imports of crude oil and petroleum products. Increase in the import of crude oil and its products as well as acceleration in oil and gas exploration and production activities on the shelf has made the coastal zone of India increasingly vulnerable to oil spills (Zingde 2001).
The rivers along the coast of India discharge about 1.56 x 1012 m3 of runoff annually to the seas transporting a wide range of pollutants of terrestrial origin. The total fertiliser consumption in India that was less than 0.1 million t/y in 1950s, increased dramatically in 70s and thereafter, with the consumption in 1999-2000 estimated at 18.37 million t (Zingde 2001). It is well established that a considerable fraction of nutrients applied on land, particularly nitrate, is washed to the sea through river runoff thereby increasing the productivity potential of the marine area that, in the long run, can considerably modify the marine ecosystem (GESAMP 2001).
The consumption of pesticides also increased phenomenally - from 5000 t in 1950 to over 84,000 t in 1998-99. Today India is the largest manufacturer of basic pesticide chemicals among the South Asian and African countries next only to Japan and along with China accounts for more than 10% of the total world production. The use of BHC that formed 20-30% of the total production of pesticides in the country during 1995-97 was banned in 1997 and the use of DDT has been restricted largely to malaria control (Zingde 2001). As in the case of fertilisers, a fraction of pesticides applied on land is transported to coastal waters through runoff (GESAMP 2001).
Another source of nuisance particularly on the beaches near cities and towns in India is the discarded plastic materials. The consumption of plastic, which was negligible in 1950s, has gone up exponentially to 2.2 million t in 1997-98 (Zingde 2001).
A fairly comprehensive database has been generated for the coastal water quality through the national program 'Coastal Ocean Monitoring and Prediction Systems' under which openshore waters up to a distance of 25 km from the shoreline are periodically monitored at pre-decided transects. National Institute of Oceanography is the major participant in this programme and monitors coastal water along the West coast of India. Independent site specific investigations at a number of locations have also been carried out along the coast by several other agencies. An assessment of the available results indicates that the openshore waters, about 1 km away from the shore, are clean and healthy except in some isolated pockets around coastal cities where degradation has spread a few kilometers further. Several inshore regions such as estuaries, creeks and bays however, have been degraded to a varying degree depending on the fluxes of pollutants they receive and their flushing characteristics. Domestic wastewater is the major source of pollution though industrial emissions also contribute locally in some instances (Zingde 1999).
Inshore waters of Mumbai and region around, particularly Versova Creek, Mahim Creek, Ulhas estuary, Thane Creek and Patalganga estuary, are the examples of highly degraded environment because of anthropogenic perturbations. Several other inshore waters also reveal varying degrees of ecological deterioration. These include Veraval, Porbandar and Visakhapatnam harbours, Mahi, Mindhola, Purna, Par, Ambika, Auranga, Kolak, Damanganga, Ulhas, Savitri, Kundalika, Vashisti, Ashatmudi and Ennore estuaries, interior Kochi Backwaters and coastal waters of Chennai. Excess organic loading, often associated with the release of untreated or partially treated domestic wastewater, is largely responsible for this degradation. (Zingde 1999).
Marine sediments of the Indian coast are by and large free from gross contamination by heavy metals such as Co, Ni, Cu, Zn, Pb, Cd and Hg (NIO 1997) though a few localised areas have been reported to have accumulated trace metals. Some examples are: Cr and Hg in Par estuary, Hg in Mindhola estuary, Cr, Cu, Zn, Pb, Cd and Hg in Ulhas estuary (Sahu and Bhosale 1991) and Ni, Cu and Zn in Visakhapatnam harbour (Satyanarayana et al 1994). Mercury levels of 60 ppm have been found (Ram 1999) in the surficial sediment of the interior Ulhas estuary which progressively decrease in the seaward direction with the sediment of the mid-estuarine segment sustaining the concentrations of about 0.6 ppm and the baseline (0.1 ppm) is attained several kilometres off in the sea from the mouth of the estuary. Caustic soda industry is considered to be the major source of Hg to the marine environment.
Except in a few cases of elevated concentrations of some toxic metals in marine organisms localised to a few wastes receiving sites, the commercial fish and shellfish is free from heavy metal contamination. Uptake of DDT and Aldrin by marine organisms to levels to cause concern is also not indicated though the results are not exhaustive (Zingde 2001). The levels of petroleum hydrocarbons in water (< 20 m g/l) as well as sediment (<10 ppm) in some port areas though show a marked enhancement as compared to those at the openshore regions, they do not reveal accumulation in organisms (Chouksey 2002).