Rare species to help revive mangroves

Rising water pollution combined with increased siltation along mangrove forests is leading to the dominance of only one species in Mumbai and Maharashtra — the grey mangrove (Avicennia marina) — which is wiping out all other rare and threatened flora that once flourished along this coastline.

To counter this and ensure balanced species diversity, the Maharashtra government has begun planting 10 rare and uncommon species at different mangrove forests in the city, and 15 species along the Konkan coast that were once found in abundance.

While Lumnitzera racemose, Sonneratia caseolaris, and Avicennia alba were earlier dominant along Bandra’s mangroves forests and other areas along the western suburbs, they have not been documented since 1957. Kandelia candel was lost spotted along the eastern suburbs as early as 1905. Since then, these species remain missing from Mumbai. A similar case is being witnessed for other common species as well over the past decade. This has been documented under a study by the Indian Council of Agricultural Research - Central Institute of Fisheries Education (CIFE) in Versova.

The combination of untreated sewage and domestic waste entering our rivers, creeks and ultimately the sea is proving fatal for these salt-tolerant trees, said officials from the state.

“We have made our water bodies so polluted that other species are unable to survive,” said N Vasudevan, additional principal chief conservator of forest, state mangrove cell. “We should be concerned that the mangrove variety of Mumbai is getting eroded slowly, and we are only finding a single species diversity.”

The state mangrove cell will be planting 10 lakh saplings (three lakh has already been planted between July and September) of species such as — Lumnitzera racemosa, Kandelia candel, Sonneratia caseolaris and Avicennia alba — among others. “We have been growing these rare and threatened species across three state-owned nurseries at Airoli in Navi Mumbai, Erangal in Malad, and a site close to Ghodbunder Road,” said Vasudevan. “Plantations are being done on degraded forest areas, compensatory land allotted for development projects, and creek edges where high siltation is naturally altering the ecosystem.”

Some of the plantations have been carried out across areas like Bhandup, Mankhurd, Charkop, Borivli, Kandivli, several locations in Navi Mumbai, including land owned by the City Industrial Development Corporation Ltd (Cidco), said Vikas Jagtap, divisional forest officer, mangrove cell.

The grey mangrove has high tolerance level to poor water quality and thrives on nutrients it gathers from low oxygen and high turbidity. “While being highly resilient, there are some problems. Their small breathing roots get covered during excess siltation. While they do not survive in such circumstances, they also don’t allow other plants to take their place. Also if the water level is rising, the area under permanent convergence increases and the roots get submerged. Such areas need to be replaced with species that have longer breathing roots.”

Experts said abundance of the grey mangrove was not just along Mumbai and Maharashtra but the entire Indian coastline. “Over the past 25 years, this species has literally changed India’s overall mangrove biodiversity because it can sustain difficult survival conditions,” said V Sundararaju, retired IFS officer and president, Society for Conservation of Nature, Tiruchirappall , Tamil Nadu. “However, the steps being taken by Maharashtra are in the right direction but they need to ensure only indigenous mangroves are planted or else the entire vegetation will change again.”

Annam Pavan Kumar, senior scientist, CIFE-Mumbai, said, “This process should be done scientifically by studying location wise pre-pollution diversity of Mumbai and replicating plantation in the same areas now. In a multi-species biodiversity, each mangrove plant contributes towards the safety of an entire ecosystem individually and allows marine life to proliferate. However, presence of one species is always dangerous as the ecosystem can be wiped out completely if that species is lost.”

First Published: Sep 09, 2019 00:30 IST