Status of Indian Mangroves: Pollution Status of Pichavaram Mangrove, Southeast Coast of India
An. Subramanian

Introduction

The Indo-Malaysian area is considered as the cradle of evolution of mangrove ecosystem (Krishnamurthy, 1993), because it is widely believed that the mangrove plants developed first in this area and then only spread to other regions of the tropics. At present the Indo-Pacific region is known for its luxuriant mangroves. Especially the mangrove forests are most luxuriantly present in Southeast Asia. The Sunderbans of India and Bangladesh put together form the single largest block of mangroves of the world.

India has a very long coastline with very much variable ecological features. A recent Government of India publication states that the total length of the Indian coastal zones are 7516.6 km, including the island territories.To undertake National Programmes for the conservation of Indian mangroves and associated flora and fauna, there is an urgent need to highlight or emphasize the essentiality of Indian mangroves. For such a work, the Indian mangroves should be treated as critical ecosystem and studied in detail, case by case.

Indian mangroves have a long history. Even from upper cretaceous to miocene period, there was a luxuriant existence of mangrove vegetation along the Indian coast, which is evident from the available fossil specimens of mangroves.

Probably, Portuguese were the first foreigners to visit Indian mangroves around 14th century. They learned the technique of using mangroves to create rice-fish-mangrove farms and taught the technique to the people of African countries such as Angola and Mozambique (Vannucci, 1997). The first scientific report on Indian mangroves - gHortus Bengalensish was published in 1814 by Roxburgh in which he described the flora of Sunderbans mangrove. In 1891, Schimper published a classical work gDie Indo-Malayichen Strandflora" followed by publications by Clarke (1869), Prain (1903), Blatter (1905), Cooke (1908) etc. The management practices of mangroves were also first started in India in the 19th century in the Sunderbans, for timber (Vannucci, 1997), which were later adopted in Malaysia and Indonesia.

Hooker in his book "Flora of British India" (1872-1897) explained several geographical divisions of India based on plant types. The works of Champion (1936) and also of Gamble (1936) are some of the works describing the phytogeographic regions of preindependence India.

One decade after independence of India, the importance of these areas have been felt. The Government of India has introduced a scheme for conservation and protection of the mangrove ecosystem and set up the national experts panel on the mangrove ecosystems. Prior to this, several meetings and symposia were held and the published proceedings of the same have highlighted the status of Indian mangroves, their decline and have also warned the urgent need for conservation and preservation of these coastal endangered ecosystems.

A status report on gMangroves of Indiah was brought out in 1987 by the Ministry of Environment and Forests (Anon, 1987), which has described the mangrove formations all along the east and west coast and also in the coastal regions of Andaman and Nicobar islands.

As a result of several activities carried out by the expert committee, several major and minor publications have been published (Bhosale, 1986; Deshmukh and Balaji, 1994). The need was felt for updating the status report and much more work has come out since then (Anon, 1997, 1998, 1999, Kathiresan, 1992, 1995; Kannan, 1996; Gopal and Krishnamurthy, 1993). The coordination of global mangrove research through ISME (International Society of Mangrove Ecosystem) with a base at Okinawa (Japan) was first presided by Dr. M.S. Swaminathan, an Indian.

This foundation initiated a pioneering research on mangrove genetic resources in 1991. It has also identified 23 sites from nine countries - Cameroon, India, Indonesia, Malaysia, Papua New Guinea, Pakistan, Philippines, Senegal and Thailand for isolating genetic material conferring salt tolerance from mangrove species and transferring them to crop plants, in future. The four sites identified in India are Bhitarkannika, Coringa, Goa and Pitchavaram.

According to a status report of the Government of India publication, the total area of the mangroves in India, was reckoned at about 6,740 km². This covered about 7% of the world mangroves (Krishnamurthy, 1987) and 8% of the Indian coastline (Untawale, 1987). But a recent Indian Remote Sensing Data (Nayak, 1993) showed that the total area of the mangroves decreased to 4,474 km² (Table. 1). The values shown by satellite data shows a decrease in the mangrove area, which may be due to several reasons such as

Area under Mangroves in India

Recent data available from the Forest Survey of India, Dehra Dun shows an extent of 4827 sq. km. mangrove areas in India. A state-wise distribution of mangroves is given in Fig.1. Out of the total area, 57% of the mangroves are found on the East Coast, 23% on the west coast and the remaining 20% on the Bay Islands (Andaman and Nicobar).

Fig. 1 : Statewise - Distribution of Indian Mangroves ( Naskar and Mandal , 1999)

The mangroves are prominent in the east coast of India because of the nutrient rich soils brought in by the rivers - Ganges, Brahamaputra, Godavari, Mahanadhi, Krishna and Cauvery and a perennial supply of fresh water along the deltaic coast, as a result of which on the shores of the Bay of Bengal only deltaic mangroves exist. On the other hand, the west coast is characterised by typical funnel-shapped estuaries of the rivers like Indus, Tapti and Narmada characterised by creeks and backwaters and hence the backwater - estuarine type mangroves occur on the coasts of Arabian sea (Naskar and Mandal 1999). Gopal and Krishnamurthy (1993) indicated that the insular type mangroves are present in Andaman and Nicobar islands where the lagoons and neritic islets support a rich mangrove flora.

Mangrove vegetation in this coastline spread over in the maritime states Gujarat, Maharashtra, Karnataka and Kerala and are Union Territory, Goa. According to Sidhu (1963) total coverage of mangroves in the Indian west coast are about 1140 km², but the Status Report published by Government of India (Anon, 1987) emphasized that the west coast Indian mangroves are only covering an area of 850 km².

Gujarat state on the east coast has got the second largest area of mangroves along the Rann of Kutch and Kori creek. In Maharastra and Goa, mangroves exist especially in large patches along the Mandovi estuary, Kundalika estuary and several creeks. Mangroves of Karnataka cover an area of 6000 ha and the stretches of mangroves in Kerala state is only very sparse.

Andaman and Nicobar islands in Bay of Bengal harbour a rich variety of mangroves to about 770 sq. km. which are found along the creeks near bays and lagoons with dominant species Rhizophora mucronata, Avicennia spp., Ceriops tagal etc. (Singh et al., 1986).

Pichavaram mangrove forest is located about 200 km south of Chennai (Madras) city in the southeast coast of India. This mangrove is actually sandwiched between two prominent estuaries, the Vellar estuary in the north and Coleroon estuary in the south. The Vellar - Coleroon estuarine complex forms the Killai backwater and Pichavaram mangroves (Fig. 2).

Pichavaram mangrove (Lat. 11‹ 21fN; Long. 79‹ 50fE) is present in the higher land of Vellar-Coleroon estuarine complex. The mangrove extends to an area of 1,100 hectares, representing a heterogeneous mixture of mangrove

elements. The source of freshwater to this mangrove is from both the estuaries and that of seawater is Bay of Bengal.

Fig 2 : Pichavaram Mangrove - Southeast Coast of India

The whole of the mangrove comprises about 51 small and large islands with their sizes ranging from 10 m² to 2 km ². The mangrove soil usually consists of alluvium derived from the mangrove plants. About 40% of the total area is covered by water ways, 50% by forest and the rest by mud flats, sandy and salty soils. There are numerous creeks, gullies and canals traversing the mangroves with a depth ranging from 0.5 to 1.5 m and discharging freshwater into the system. A major irrigation channel is mainly discharging agricultural waste water from the entire upper reaches to this mangrove.

Pichavaram mangrove did not receive much attention during pre and post independence periods. A map published by the Cuddalore District authorities in 1882 is the document which was first made available to public. Then, only during the later part of 20th century (Thirumalairaj, 1959) explored the Pichavaram mangrove and Venkatesan (1966) listed the floral communities in the region in relation to environmental factors.

French institute, Pondicherry is one of the pioneering institutes in exploring Pitchavaram and contributed several publications on the wealth of the mangroves (Blasco, 1975; Meher Homji, 1979)). The Centre of Advanced Study in Marine Biology, right from its inception in 1961 has been involved in various research activities in Pichavaram mangrove. Water quality, floral and faunal composition, microflora, ichthyofauna, bioactive substances from mangroves, fishery resources, larval development, heavy metals and organochlorine residues, methanogens, cyanobacteria, wood biodeterioration and UV - radiation are all studied extensively by this Centre. During 90s, M.S. Swaminathan Research Foundation (MSSRF), Chennai, India established a mangrove Genetic Resource Conservation Centre here by adopting 50 ha forest area. In addition, Centre for water Resources, Anna University, Chennai has remotely sensed Pichavaram forest with satellite imageries

The mangrove flora in India comprises 35 species under 16 genera and 13 families. Of these 33 species (16 genera and 13 families) are present along the east coast (Kathiresan, 1998). The east coast of India and Andaman and Nicobar islands show high species diversity.

Pichavaram mangrove is one of the rare mangrove forests in India and it represents 14 exclusive mangrove species (Kannupandi and Kannan, 1998). Avicennia marina alone constitutes nearly 30% of the total population followed by Bruguiera cylindrica (17%) and Avicennia officianalis (16%). The population density of other species is poor and many of the species are on the verge of total extinction.

According to a recent statistics, it is found that nearly 62.8% of the Pichavaram mangrove forests were degraded between 1897 and 1994.

Tissot (1987) investigated the change that has taken place in the vegetation of the Kaveri delta over a period of 2000 years. It has been found that the breadth of the beach protecting the mangrove areas from wave action at Pichavaram mangrove has reduced by 550 m between 1970 and 1992.

The substantial reduction in the forest cover is due to frequent cyclones atleast every alternate year which devasted several mangrove species and reduced the total area from 4000 ha in the beginning of the century to nearly 1100 ha at present.

As a result of this, many plants previously recorded from Pichavaram mangrove have completely vanished. For example, the pollen analysis of the sediments from Pichavaram showed that Sonneratia was abundant here in the past (Caratini et al., 1973), which is on the verge of extinction at present. Further, occurrence of Aegiceras flordium reported from this area by Krishnamurthy (1978) could not be confirmed by Muniyandi (1985). Certain species like Xylocarpus granatum, Rhizophora stylosa and Bruguiera gymnorrhiza which were once collected from this mangrove are not available at present (Kannupandi and Kannan, 1998). It is also found that most of the individuals of Rhizophora sp. are aged and the rate of reproduction is also low at Pichavaram mangrove. It seems to be on its way to extinction at this mangrove, being replaced by the much more dynamic Avicennia marina (Kannupandi and Kannan, 1998).

From the Pichavaram mangrove ecosystem about 100 species of diatoms, 20 species of dinoflagellates, 40 species of tintinnids, 30 species of copepods, 30 species of prawns, 30 species of crabs, 30 species of molluscs and 200 species of fish have been recorded (Anon, 1987).

Innumerable studies are available on the chemical aspects of this mangrove from 1960's that is from the coming into existence of the Centre of Advanced Study in Marine Biology of Annamalai University. Simultaneous investigations on the Vellar - Coleroon estuarine complex, all the four aquatic biotopes viz., the mangrove waterways, the adjacent Killai Backwater, the Vellar and Coleroon estuaries and the neritic waters of Bay of Bengal, revealed that certain environmental and meteorological factors exert remarkable influence in this mangrove biotope (Anon, 1987).

With normal (130 cm) and abundant (>130 cm) rainfall, the mouths of the mangrove and estuaries become deep and remain well open to receive considerable volume of neritic inflow particularly at high tide and hence the mangrove ecosystem function more like a coastal marine ecosystem, whereas in the lean years of rainfall, the mangrove ecosystem functions more like a freshwater or limetic ecosystem.

The neritic influence in the mangroves is felt for a distance of about 10 kms. The maximum depth in the waterways is about 1 m. The salinity varies from 0 to 34 ppt. The annual temperature range was from 20 to 34‹ c. The pH ranges between 7.60 - 8.50 showing the alkaline nature of the water. The dissolved oxygen content was on an average about 4.5 ml/l.

With regard to pollution studies, the earlier works done by Ramadhas et al. (1975), Sundararaj (1978) Ramadhas (1977), Subramanian (1982), Subramanian et al (1981, 1983) are worth mentioning.

Subramanian (1982) and Subramanian et al. (1983) found that the salt excreting type of mangrove Avicennia marina accumulate more of iron and phosphorus in the leaves than the salt excluding species Rhizophora mucromata and also found a clear seasonal fluctuation. Subramanian (1982) found very clear seasonal fluctuation in the concentrations of Fe, Mn, Cu and Zn in the environmental compartments such as dissolved, particulate and sediment fractions and found the sediments of mangrove which is normally rich in organic matter as a prime sink for these elements that are being brought in by freshwater. Generally the reactive forms of trace elements in the water was higher during monsoon season in this mangrove indicating the importance of freshwater in enriching these waters with essential nutrients.

The animals like the oyster Crassostrea madrasensis , the polychaete Nereis costae had their higher concentrations of trace elements in the monsoon months. Again, in the case of mangrove plants also, salinity seemed to be the dominant factor in controlling the uptake and accumulation of the elements (Subramanian, 1982). A recent data obtained from Pichavaram mangrove on several physico-chemical parameters (Table.2) showed that this mangrove is still pristine and the values are very much within optimal levels (Balasubramanian, 2000 Personal communication).

Physico-chemical parameters observed in the Pichavaram mangroves during June 1999 and October 1999. (Balasubramanian, Personal communication)

Earlier workers like Karthikeyan (1988) revealed their concern after finding considerable concentrations of the pesticides like DDTs, Lindane (

Inspite of the increased usage in the past decade, the concentrations of DDTs (p, pf - dichloro diphenyl trichloro ethane) and HCHs (Hexachlorocyclohexane), the two major pesticides which have been used until recently in India, their levels in the Pichavaram mangrove water (Fig. 3) and sediment (Fig. 4) are within normal limits. There was a clear seasonal variation showing the clearing away of these volatile residues via. monsoonal rains or atmospheric passage (Takeoka et al., 1991) (Fig. 5).

Fig.4. Spatial distribution of DDT in the Pichavaram mangrove and Vellar estuary during the dry (above) and wet (below) seasons. Ramesh et al. (1990)

The research work done by the scientists of the Centre of Advanced Study in Marine Biology and M.S. Swaminathan Research Foundation showed that contamination by various chemicals is not in abnormal levels and is not adding any pressure on this mangrove ecosystem.

Figure.5 Schematic representation of the flux of HCH

in the Vellar watershed.

Takeoka et al. (1991).