On World Oceans Day, naturalists unveil Chennai’s marine biodiversity

Hooked Nosed Sea Snake. Photo: Vikas Madhav Nagarajan  

From the last quarter of 2020 to the first of 2021, a six-member team of young nauturalists — which Madras Naturalists’Society honorary secretary G Vijay Kumar dotingly terms ‘Chennai’s own Ocean’s Six’ — explored five biodiversity hotspots: Pulicat Lagoon, Adyar Estuary, Kovalam-Muttukadu Backwaters, Odiyur-Mudhaliyarkuppam Lagoon, and Kaliveli Lake-Yedaiynthittu Estuary. This tiny group would move around, splintered into tinier bits of 2s to maintain social distancing.

Vikas Madhav Nagarajan, a member of Ocean’s Six, underlines what came of the effort orchestrated in the middle of a crisis that is arguably the most crippling ever for the entire world: 709 species from eight classes — crustacea, mollusca, echinodermata, arachnida, insecta, reptilia, aves and mammalia — were encountered in these areas. With 204 species from a previous study, the tally for these five hotspots is now pegged at 913 species.

On the high points, Vikas says: “We also dealt with smaller forms of life that are generally not well-studied like echinoderms and tunicates. We found rare records of birds like the grey-tailed tattler (Kaliveli), grey-lagged goose (Kaliveli) and the eastern yellow wagtail (a bird that has been reported only as recently as last year) which we found in two places. We got several data-deficit crabs such as dardanus imbricatus (floral-clawed hermit crab) and dardanus hessii (red-socked hermit crab). In the Indian Ocean waters, much of the study about these crabs has been carried out in Arabian Sea, and only a little in the Bay of Bengal.”

Golden tunicate. Photo: Vikas Madhav Nagarajan

Golden tunicate. Photo: Vikas Madhav Nagarajan  

The effort is part of a Bunyanesque exercise by Madras Naturalists’ Society (MNS) to study the Tamil Nadu coast for its marine biodivesity and the threats to it.

The state’s coast has been spliced into four zones: Zone One, also called North Tamil Nadu coast, was marked with Pulicat Lake and the Kaliveli Lake-Yedaiyanthittu Estuary as its extremties. Vijay Kumar explains that in May 2020, a study of literature pertaining to this zone was undertaken and in September 2020, marine biologist Suneha Jagannathan put the team through a primer on how to collect the data, which includes the transects to be used.

The Zone One study in the can, MNS has unveiled the findings of the study for the larger world, along with the release of a field guide on marine fauna of Chennai and surrounding coastal sections, to mark World Oceans Day (June 8). The field guide can be downloaded from

KV Sudhakar, president, MNS, places it in perspective: “For the last couple of decades, media has been occupied with species reporting, highlighting fauna, avifauna and flora (found inland) to the point of ignoring an important aspect of Tamil Nadu, which is its coast. It is glaring that the focus on marine biodiversity is at a low ebb. So, MNS has decided to celebrate World Oceans Day in this manner.”

During the study of Zone I, the above-mentioned five sections came into focus for their ecological significance. Except for Adyar Estuary and Odiyur-Mudhaliyarkuppam Lagoon, these sections are designated Important Coastal and Marine Biodiversity Areas (ICMBAs). Vikas remarked that it is a matter of rejoicing that so many marine life forms are found on the coast of a metropolitan city (Chennai). In the same breath, he presented a sobering picture of coastal erosion and pollution.

Murex Snail. Photo: Vikas Madhav Nagarajan

Murex Snail. Photo: Vikas Madhav Nagarajan  

“Two most important threats encountered during the study are: Coastal erosion, prevalent in the Kovalam-Muttukadu area and Pulicat. If we are going to have rapid industrialisation along the coast which will cause more groyne formation, there would be more soil erosion precipitating the ecological degradation of the entire zone. If Pulicat is affected, the northern zone would be affected in its entirety,” says Vikas. “The next threat is pollution, which can come in any form. The five places registered different types of pollution. In Pulicat, there was a mixture of water pollution and domestic waste pollution. In Adyar Estuary, it is mainly poorly treated effluents. In Kovalam, it was municipal domestic waste. In Odiyur and Kaliveli, we found minor threats of pollution, mainly from microplastics.”

The report notes that these areas support 34 globally threatened species, including the endangered Indian Skimmer, Great Knot and the Indian Pangolin.

“The Great Knot, classified as an endangered species, visits three of the five places we surveyed. The Great Knot is facing considerable pressure in its breeding grounds in Russia and Mongolia. These kinds of migratory routes are very important. If these are polluted, the stress on the bird increases further and does not augur well for its survival,” elaborates Vikas. “We are recommending that Adyar Estuary and Mudaliarkuppam backwaters also be designated as ICMBA, because they have rich biodiversity and meet the criteria for ICMBA classification as spelt out by the Wildlife Institute of India (WII).”

Yuvan M, another Ocean’s Six member, observes that though the coastal habitats have been hit by strong weather events in recent times, they also offer “protection against these events, being a bulwark. For instance, when we went to Mudhaliarkuppam and Odiyur, we found that the sand dunes there are extremely well-developed — some of them 30 feet high. The local people told us that when the 2004 Tsunami came, the dunes had this capacity to constantly draw in the incoming tidal waves and not allow it to reach the village. There have been similar stories about mangroves and oyster reeds holding and binding the coast.”

Yuvan underlines how the study would seek to tap into native wisdom of the local people.

“When we say hotspots we are looking at what have been declared as ICMBAs by the WII, and also other hotspots which local people know as sustaining a sufficient amount of biodiversity. And we are exploring how to involve the public, schools, fisherfolk, and other common members of society in the study and documentation.”

Vijay Kumar defines this study as hugely significant, basing the inference on the fact that there has not been many preceding it.

“The exercise to define ICMBAs along peninsular India was taken up by Wildlife Institute of India just in 2014, and this was after IUCN urged all coastal countries to do this. Their method of identifying an ICMBA was based on already published data and they had very broad criteria to determine what constituted an ICMBA. During our study, we found out that Adyar Estuary and Odiyur also qualified to be ICMBAs. We were able to get data from other sources; and there were several new records that we were able to see,” the honorary secretary explains.

In response to a question about noticeable habitat degradation, Vijay Kumar says:

“Pazhaverkadu (Pulicat) derives its name from the fact that there are mangroves — today, mangrove concentration in this coastal belt is down to zero. Except for a section of Pulicat on the Andhra side, the mangroves have gone. So, mangrove-dependent fauna will not be found.”

On the long-term significance of the study, he says: “Biodiversity and Human Well-being is now collecting biodiversity data right across the country to create a repository, into which the data we would be collecting in the next one year would go.”

(Anooja A, Aswathi Asokan, Nanditha Ram Satagopan and Rohith Srinivasan are the other members of the team that carried out the field study)

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Printable version | Jan 20, 2022 1:48:23 PM |

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