Know and grow your mangroves: A primer for the residents of Chennai

Well ahead of International Mangrove Day, a look at the richness of the intertidal patches that support these wonder plants

July 17, 2021 10:58 pm | Updated 10:58 pm IST

File Photo: S.R. Raghunathan

File Photo: S.R. Raghunathan

Chennai residents need to wrap their head around avicennia marina ’s pneumatophores (imagine upturned roots sticking out of a watery soil) as also rhizophora ’s roots (think of the Banyan's aerial root system; or more aptly, wildly hanging dreadlocks). These are the two species that predominate the mangrove patches in the intertidal areas on Chennai’s coast. On patches where they are founded, these mangroves should increase. On patches where they could thrive but are not found, they should be made to put down those gnarled and quirky roots.

What mangroves can do for the safety of coastal residents is widely appreciated, thanks to sufficiently-amplified accounts of how mangrove forests stood up to 2004 Indian Ocean Tsunami, on sections of the Tamil Nadu coast. In contrast, their ability to enhance coastal biodiversity and improve the livelihoods of coast-dependent populations is not as widely understood, let alone utilised.

Any time is always propitious to mull over these facts and match cogitation with effective action. However, given the significance attached to special days of observance, this season (United Nations observes July 26 as International Day for Conservation of Mangrove Ecosystem) is even more suitable for this exercise.

Here are two subject matter experts, each from a different sphere of operations but united by shared conservation goals, deconstructing the mangrove ecosystem, in the context of the Chennai coast.

M Masilamani Selvam is associate professor of biotechnology of Sathyabama Institute of Science and Technology, and author of the Tamil book on mangrove forests, Alayathi Kadugal. Masilamani has trained under a luminary on mangroves, being a student of the legendary K Kathiresan at Annamalai University.

M Yuvan is a naturalist and author of A Naturslist’s Journal and is in the forefront of an ongoing study on Tamil Nadu’s coastal biodiversity being undertaken by Madras Naturalists’ Society.

“Mangroves are found in the Kelambakkam and Kovalam backwaters. I notice some positive signs in the Kelambakkam backwaters, on the connecting road between Kelambakkam and Kovalam. Initially, it was pretty dry and there was a lot of grazing. Now, it is flourishing, with patches of dense mangrove growth, particularly in the last two to three years,” observes Masilamani.

Yuvan weighs in about how the mangrove ecosystem in this region meets livelihood needs, as is evident from the “handpicking” on the Kelambakkam section of Muttukadu.

“With baskets, handpickers can be seen in the mangrove patches looking for prawns , giant mud crabs ( scylla serata ) and mullets,” Yuvan notes.

“The problem with the Muttukadu backwaters is that a huge amount of domestic waste is coming inside. So, many life forms are vanishing. The Wildlife Institute of India (an autonomous institution of the Ministry of Environment, Forest and Climate Change, Government of India) has described it as an Important Coastal and Marine Biodiversity Area (ICMBA) for various reasons — there are birds, mangroves and sand dunes,” states Yuvan while underlining the need to protect the ecosystem. Another intertidal patch marked by noticeable mangrove growth lies well within city limits — Adyar Estuary. Masilamani draws attention to how a part of the mangrove forest in this estuarine habitat is the result of a planting exercise.

Though it is unclear how big a part this is, it does broadcast the fact that people can and should have a hand in mangrove regeneration.

For anyone who may be curious enough to want to clap eyes on this urban mangrove forest, there is an unhindered view of it available from the broken bridge side. A shock of mangroves is found along the border of the Theosophical Society premises. There is avicennia marina and rhizophora to gaze at.

While pointing out that the Tamil Nadu side of the Pulicat lake has lost its mangroves to prosopis juliflora , Yuvan notes: “In Senjanimedu and Ennore creek, mangroves are still found — largely avicennia marina and a little bit of rhizophora .”

A closer look

“While avicennia marina and rhizophora are both intertidal plants, the latter is found more towards the waters than the land. When you travel further into an intertidal area by boat, you would get to see rhizophora . Even during low tide, you would find rhizophora in the water only, but in contrast, avicenia marina will be seen exposed,” says Masilamani. “Behind these two, a commonly seen mangrove plant is excoecaria agallocha . There is a tendency among some botanists to categorise it as a land plant, but it is a mangrove, fair and square. It would largely be found in sandy shores, mostly in the brackish water area.”

The benefits

Even if they occupy a small patch of intertidal area, a clutch of mangroves comes with the facets of a complex ecosystem. “The main benefit of having mangroves is the fishery resource they automatically create. Prawns are directly related to mangrove ecosystems. They are drawn to the mangrove environment for the highly complex web-like structure it provides for the young ones to hide away. Mangroves serve as a nursery for young fish and shrimps. The leaf litter would be there all the time, degrading and decomposing and therefore promoting the fauna of the subsoil. It is an environment that supports small worms and insects, on which the small fish and shrimps feed,” explains Masilamani. “Mangroves draw crabs, which graze the leaves and the leftovers go down and degrade, providing food for the molluscs. Dependent organisms develop automatically. Where there is biodiversity, the ecosystem will flourish.”

Here is the crux of it, in Masilamani’s words:

“On the Chennai coast, the focus should be on planting mangroves wherever it is possible to do so, as we are cyclone-prone. With mangrove plantation, 50 percent of the damage can be reduced. When they grow very high, mangroves can serve as effective wind breakers.”

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