Monday, Dec 05, 2022

An Expert Explains: How rare species of Sundarbans are threatened by human activities

Settlement mangroves which used to be safe havens of diverse molluscs and crustaceans are disappearing due to the polluted discharges from shrimp ponds

Mangroves_of_SundarbansThe continued loss of shoreline mangrove ecosystems has created fragmented and fragile mangrove habitats for rare taxa and framed barriers to their movement and dispersal. (Wikimedia Commons)

Our world recently completed the ‘United Nations Decade on Biodiversity (2011-2020)’ and we have started to realise that biological diversity plays a key role in ecosystem functioning and is essential for human well-being and local livelihoods.

Despite every effort made nationally to motivate actions in support of biodiversity conservation in all ecosystems, continuous loss of biodiversity is observed across the shorelines of settlement zones in Indian Sundarbans. This region harbours many rare and threatened flora and fauna which maintain the mangrove ecosystem’s integrity and complexity.

The Expert

Krishna Ray is an assistant professor at the Department of Botany, West Bengal State University

Small patches of mangroves are being lost gradually and quietly due to their indiscriminate destruction for either coastal development or short-term gains. The loss of relatively small patches of mangroves may seem less perilous than large-scale deforestation. However, these patches are observed to be enriched habitats of several rare and threatened flora and fauna.

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The continued loss of shoreline mangrove ecosystems has created fragmented and fragile mangrove habitats for rare taxa and framed barriers to their movement and dispersal. This irreversible loss of biodiversity is often neglected, which could never be compensated with any ‘cut the established and plant the new’ theory.

Hub of coastal fisheries

Coastal mangrove habitats across the world are the preferred hub of coastal fisheries, aquaculture, pisciculture, shrimp farming, crab farming, all providing livelihoods to local people. In Indian Sundarbans, conversion of shoreline mangroves to shrimp farms and other pisciculture farms is very popular and it is the main source of income for the local people.

However, these livelihoods come at the cost of frequent clearing of the shorelines once occupied by native mangrove species. Thus, the habitats of many species continue to be reclaimed for shrimp culture, in spite of knowing that mangrove destruction could also be counter-productive, as the shrimp industry depends on various ecological services provided by the mangrove ecosystem in order to maintain its continued productivity.


The building of dykes for the protection of coastal villages from tidal aggression/storm surges is another major cause that makes mangrove communities across the estuarine shorelines in the settlement regions of the Sundarbans, the most vulnerable targets of destruction.

Extensive surveys for the last few years (2014-2021) by our group observed that loss of these mangrove habitats also leads to loss of species that belong to IUCN’s near-threatened or endangered category.

These settlement mangroves used to be safe havens of diverse molluscs and crustaceans, but these are also disappearing due to the polluted discharges from shrimp ponds, harming the native habitat and breeding activities of these species. One such crustacean is a sesarmid mangrove tree-climbing crab called Episesarma mederi, rarely reported from Sundarban settlement mangroves.


Instead of popularising shrimp farming, if more indigenous fishing activities were encouraged, we could protect both our coastal threatened biodiversity and at the same time provide livelihood options to the coastal dwellers.

The accreting mudflat is a favoured habitat for mangrove-dependent fish species, which enter the mudflat with the tidal flow but are trapped in these nets during the ebb current of the tides.

In Vietnam, 100 km of concrete sea-dyke buffered with 9,000 hectares of reforested mangroves in front, proved worthwhile. The co-benefits of these nature-based strategies without perturbing the coastal development and local livelihood options will result in protecting biodiversity in the long run and would keep pace in developing eco-resilience of the Sundarban mangrove ecosystem to confront future climate change scenarios.

(Written as a prologue of Newton Bhabha Fund Researcher Link Workshop, to be held in November, 2021 on ‘Building Ecological Resilience in Vulnerable Mangroves of the Indian Sundarbans: Sustainable and Equitable Management of Biodiversity and Ecosystem Services in the era of Climate Change’)

First published on: 22-09-2021 at 07:58:37 pm
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