Sunday Special | Kolkata

Barren island on Hooghly estuary turns into bountiful habitat

New bloom: A satellite image of the island in the middle estuary of the Hooghly river.   | Photo Credit: Special Arrangement

Till 1990, Nayachar, a newly emerged island in the middle estuary of the Hooghly river, was completely barren, with hardly any plant or animal species. The land mass, which falls under West Bengal’s Purba Medinipur district, was created in the Indian Sunderbans by river silt deposits, and remained largely submerged, rising occasionally above the water level.

Now, an October 2017 publication by the Zoological Survey of India (ZSI) titled ‘Studies on the Succession and Faunal Diversity and Ecosystem Dynamics in Nayachar Island Indian Sundarban Delta’ has listed 151 animal species on the island, making it a rare case in ecology.

“This publication is unique in nature as it reveals how an emerging landmass can gradually provide habitats for diverse groups of organisms,” Dr. Kailash Chandra, Director of ZSI, told The Hindu. Dr. A. K. Hazra, ZSI’s former Additional Director, who has been working on the project since 1989, said that the study is perhaps the first of its kind in India, adding, “It is aimed at understanding soil stabilisation in an emerging island [and] the succession of living organisms in a new habitat.”

First survey

“In 1989, when we first surveyed the island, we found only three invertebrate soil fauna (organisms living under the soil). After a couple of years, the number doubled and, by the late Nineties, we recorded 76 invertebrate fauna, both underground and terrestrial. The data we have so far places the number of animal species at 151,” Dr. Hazra said of the study spanning over nearly three decades, from 1990 to 2017.

Dr. Gurupada Mandal, scientist with ZSI and an expert on subsoil invertebrates, said that soon after the emergence of protista (single-celled organisms) on the island, scientists could record salt-tolerant micro fauna from the Acarina and Collembola groups living under the soil.

“Nayachar is a mangrove ecosystem and the species succession we have observed here is unique. So far, we have recorded about 20 species of microfauna, which represent eight species of Acarina and six species of Collembola,” Dr. Mandal said.

The island has not only recorded a growth in species of fauna but also increased in size over the past five decades. Nayachar’s satellite data for the years from 1967 to 2015 show the area of the island has increased from 17.99 sq. km. to 46.29 sq. km. within 46 years.

Increase in faunal species is seen in every group. A total of 27 species of fish have been recorded in the publication. In 1992, only 12 species of fish was reported from the island, which gets high and low tides twice a day. By 2004, the number of fish species had increased to 24. Similarly, in terms of avifauna, the number increased from six species of birds in 1992 to 27 species in 2004. The island has recorded 37 species of birds thus far.

Mammals, mostly rats, mice, bats and squirrels, have increased in number from three in 1992 to 11 at present. The island is also home to 33 species of butterflies and moths, up from only seven in 1992. “What’s interesting is that Nayachar is surrounded by water on all sides and the nearest landmass — the sinking island of Ghoramara — is about 30 km away. The natural succession of species on the island has been aided by the inundation of water during tides, and the soil brought from other places by fishermen,” Dr. Hazra said.

The 104 islands of the Indian Sunderbans, both habited and uninhabited, are distributed in West Bengal’s South 24 Parganas and North 24 Parganas districts.

Textbook pattern

Researchers point out that soil formation and subsequent changes, which led to the presence of 151 species on the island, evolved in the classic textbook pattern on Nayachar. Microfauna organic material is released by the soil, which in turn releases energy and CO2. The stepped process centres around microfauna like collembolans and mites, and leads to increased nitrification and formation of humus.

Macrofauna reported on the island is found both in the soil and in the emerging habitation cover. Insects and fish are attracted to the food available in the aquatic habitat and soil vegetation.

“This leads to an increased number of avian species,” the publication states. Experts like Dr. Hazra and Dr. Mondal point out that Nayachar, as the name suggests, is a new island, and that it is important to monitor its physical and biological changes with a continuous surveillance system, without allowing any major economic activity on the island.According to Dr. Chandra, “Nayachar has provided that rare opportunity for researchers to study species succession from a very nascent stage.”

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Printable version | Oct 23, 2020 7:15:31 AM | https://www.thehindu.com/news/cities/kolkata/barren-island-on-hooghly-estuary-turns-into-bountiful-habitat/article22387348.ece

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