Over the past five years, an uncommon mangrove species has started to dominate wetland and creek areas along the Mumbai coast – one that was barely visible a decade ago. Mangrove cell officials have recorded a threefold increase in the cover of apple mangroves (Sonneratia alba) at creek edges from 2% to 6% across Mumbai, Navi Mumbai and Thane since 2011.
Environmentalists said the increase in the mangrove cover assumes significance since these trees play an important role in absorbing pollutants in water bodies.
Wetlands across Mumbai and Thane have been witnessing large scale destruction due to encroachments, debris dumping and untreated sewage. Additionally, Thane city also harbours Asia’s largest industrial complex, effluents of which are released directly or indirectly into the creek, thereby increasing pollution and affecting growth of mangroves. A rapid biodiversity assessment report in 2015 revealed a 90% decline in the number of fishes at the Thane creek due to high levels of water pollution.
“By acting as natural filters, these mangrove species regulate water quality. Owing to the complex and dense root network, these species can trap pollutants suspended in water and absorb excess dissolved nutrients,” said Laxmikant Deshpande, a city-based environmentalist adding that they form a white wall on waterfronts shielding pollutants from entering the ecosystem.
Close to 80% of the mangrove cover across wetlands in Mumbai, Navi Mumbai and Thane is dominated by the grey mangrove (Avicennia marina) species, a year-long study by the state mangrove cell said. However, the grey mangrove species has decreased at the edge of the Thane creek.
In fact, a separate study by the cell has documented large number of the apple mangrove trees along wetlands in the Thane creek, Bhandup, Vasai and Dombivli.
“We have observed high siltation near creek edges. This is leading to the death of grey mangroves because their breathing roots are permanently submerged under water,” said N Vasudevan, chief conservator of forest, state mangrove cell.
Vasudevan added, “Since the apple mangrove has longer roots (pneumatophores) that rise above the ground, this specie breathes more oxygen, absorbs more nutrients and has a better chance of survival.”
A unique species that blooms white fragrant flowers at night, the apple mangrove is listed as “threatened” by the Centre for Floral Diversity under the union environment ministry.
It’s their pattern of germination that help this species overshadow others, said Arvind Untawale, executive secretary, Mangrove Society of India. He said, “When the fruits from this mangrove tree fall into the water, the seed-coat degenerates and disperses. Wherever there are mudflats, they start germinating very fast. The plant is also called the ‘pioneer’ because of their aggressiveness to dominate other species.”
About the apple mangroves
- They grow up to five feet with white flowers and bear distinct green apples as fruits
- The distribution of this mangrove species is confined to the western coast of India and some parts of Orissa
- The leaf extracts possess high antimicrobial properties that can be used for development of new useful drugs as antimicrobial agents for treating infectious diseases, found a 2015 study by the zoology department, Sathaye College, Vile-Parle published in the American International Journal of Contemporary Scientific Research
- Its night blooming flowers are pollinated by nocturnal creatures like bats
- Its fruits are used to make pickle