Pichavaram – the great mangrove forest of Tamil Nadu

Few people know (or care) that this favourite locale of filmmakers is a spectacular mangrove ecosystem throbbing with life

The mangrove forests of Pichavaram comprise an intriguing ecosystem


Tickets in hand, negotiations with the boatman closed, we should have been on the boat, headed for our first visit to a mangrove ecosystem. But all we could do was to gaze longingly at the dense green clumps across a vast expanse of the lagoon. The boat that was to carry us there was moored to the shore covered in blue tarpaulin. A sudden squall was depositing even more rain on the already soaked and overflowing coastline of southern Tamil Nadu and we were right in the centre of it all – at the northern edge of the Cauvery delta. 


A sudden squall threatened to drown out our much-awaited trip

Pichavaram, one of only two mangrove ecosystems located in Tamil Nadu, is approximately 75 km south of Pondicherry and 15 km from the temple town of Chidambaram. We had reached Pichavaram in the afternoon after a very enriching visit to the great living Chola temple. To be fair, the day had been fairly dry but now that we had planned to be on open water for the next four hours, it had started pouring.


Our entry into the mangroves began with the boatman negotiating one of the tamer channels
The Cauvery delta is formed when the river breaks up into multiple distributaries after Srirangam island. The northernmost distributary Coleroon (or Killidam) meets the sea near Pichavaram (the other river that drains this area is Vellar and the wetland is referred to as Vellar-Pichavaram-Coleroon wetland). The other mangrove patch is at Muthupet, which happens to be at the southernmost point of the Cauvery delta; the distance between the two is 180 km. Muthupet has a large lagoon where six distributaries discharge their waters. These mangroves are characterized by a long dry season (February to September) and high salinity.
Inside the mangroves
The shower stopped as suddenly as it had begun. We were off in a jiffy, the boatman rowing slowly and steadily across to the mangroves. Clouds streamed in from the ocean, promising more rain, but we pretended not to care. Pichavaram has almost 4,000 rivulets of varying length and width with mangroves on either side. As we entered the first, not more than six feet across, we saw the mangroves up close. They seem to grow out of water (there is not a patch of ground visible anywhere) almost like a floating forest.
The canopy weaves a tangled web, and not always a friendly one

The boatman was accomplished at clearing our way
As the boat negotiated the first turn, to our utter amazement and delight we entered a long and narrow rivulet completely wrapped in mangroves. It was like entering a green tunnel – the boatman had to row by moving the low, tangled mangrove branches out of the way. The banks of the rivulet were covered with mangrove roots reaching into the water – hundreds for every clump. The sky was swallowed up completely by the arches of these low trees and all we could see was the narrow rivulet and a vast impenetrable forest growing out of turbid water. The world had dissolved into an expanse of brown and red stilt roots (and all the shades in between) and the luxuriant green foliage of the mangroves, upon which streaks of sunlight created an impressionist canvas of rust, brown, olive, jade, lime-green and emerald.

A maze of stilt roots

In the eerie silence, as we negotiated one tunnel after another, crabs lit up the scene. They were everywhere – climbing up from the water’s edge, clinging to the trunks, hanging on to the canopy and perched in silence on overarching branches. A myriad species of crabs inhabit the forest and it was unfortunate that we knew so little about them. Soon enough we entered one of the wider channels. It was almost 100 feet across, like highways connecting the islands of mangroves. Forest towered on either side, dense and glistening in the evening sun.

The low boughs were the province of a myriad species of crabs
The east coast wetlands starting from the Sundarbans right down to Pichavaram (and Muthupet) receive a major infusion of fresh water from the rivers either throughout the year (the snow-fed Ganga and Brahmaputra) or during the northeast monsoon (Krishna, Godavari and Cauvery). Salinity levels vary through the season in proportion to the fresh water discharge but the trend is towards an increase in salinity as we move down the coast. So, while the Sundarbans have the least salinity (and the shortest dry season), the mangrove wetlands of the Cauvery delta have the maximum salinity levels and the longest dry season. Salinity (or the absence of freshwater intake) has an observed impact on biomass and species diversity. The Sunderbans and Mahanadi mangroves have 26 recorded mangrove species (out of the 33 found in India, 51 in South Asia and 68 worldwide), and high biomass due to tall low-salinity tolerant trees. But the mangrove species diversity drops to 17 for Godavari, 12 for Krishna and finally 11 for Cauvery. 


The sea-water dominated mangroves of Gujarat (with almost no fresh water infusion) have a species diversity of just eight. Further, the dominant species in all the high salinity mangroves — those of the rivers Cauvery and Krishna and in Gujarat — is Avicennia marina, an extremely saline water-tolerant species.

It has been observed that except in Andaman and Nicobar Islands, where the mangroves along tidal creeks, lagoons and bays are extremely diverse, those of the east coast are gradually being dominated by high salt-tolerant species like Avicennia marina due to changes in quantity and periodicity of fresh water. It has been found that the vegetation of Pichavaram and Muthupet wetlands used to be more diverse in the beginning of the 20th century but since the freshwater inflow was severely curtailed by the numerous dams and canals upstream on the Cauvery, Avicennia marina became dominant.

Mangroves receive an infusion of river water during the monsoon


We spent almost three hours in this verdant forest. It was a strangely hypnotic world. The dense forest growing out of the water, trees on stilts, and meditating crabs perched where we expected birds, puzzled our senses. But it was a real world, a shrinking and vulnerable patch of forest, and probably the last remnant of the much vaster mangrove forests that occupied the Cauvery Delta.


A strangely hypnotic world

Note:
Mangrove wetlands in India are in most cases the gift of east-flowing rivers. Other than the geological fact that India has no major west-flowing rivers, the east coast is gentler and wider and thus aids major rivers in creating large deltas and an accompanying network of tidal creeks and canals, and brackish lagoons where the mangroves thrive.

The major mangroves patches in India are Sunderbans (Ganga-Brahmaputra), Mahanadi (Mahanadi, Brahmini and Baitarani – the famous Bhitarkanika wetland), Godavari (the Gautami-Godavari system creates the Coringa wetland), Krishna (three islands located between Gollamattapaya and Nadimeru distributaries, and the Krishna river) and Cauvery (Pichavaram and Muthupet). The river dominated (tide-dominated in the case of the Sunderbans) mangroves of the east coast comprise approx 57 percent of India’s mangroves.

The west coast mangroves, all of which are in Gujarat (Gulf of Kutch and the Gulf of Khambat), comprise about 23 percent and those of Andaman and Nicobar Islands make up the remaining 20 percent. There are no statistically significant mangroves outside these five states (Andhra Pradesh, Tamil Nadu, Odisha, West Bengal and Gujarat) and Andaman and Nicobar islands, though small patches exist along the coasts of Kerala, Karnataka, Maharashtra and Goa.

We saw very few birds inside the forests but for the Striated Heron or the Mangrove Heron

The Gujarat mangroves are of a very different type. They are “sea mangroves” since they receive almost no freshwater from inland rivers during the year. These are classified as “drowned-valley type mangroves”.


Text and photographs by Sahastrarashmi
Additional photographs by Bijoy Venugopal


References: 


V Selvam, Environmental Classification of Mangrove Wetlands
of India [PDF]

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