Mumbai: Out of 329 live coral colonies which were translocated from the Haji Ali bay to Navy Nagar in November 2020, as a result of the Brihanmumbai Municipal Corporation’s (BMC) Coastal Road project, 303 colonies (or 92% of the total) were found to have survived in a healthy state a year later, as per a newly published study by researchers at the National Institute of Oceanography (NIO).
Notably, the study also finds that the translocated corals are propagating, with the recruitment of 22 new corals on the rocks of the transplanted colonies. Eleven coral colonies (or 3.4% percent) have not survived the translocation, while the remaining were found to be partially bleached. The coral colonies have been affixed to 194 different rocks and boulders.
Experts working on the study, and officials with the state forest department’s mangrove cell, have maintained for more than a year that the translocated colonies are healthy. However, this study — titled ‘Translocation of intertidal corals in highly urbanised Mumbai seascape: A pragmatic management initiative towards ecosystem conservation’ — marks the first time that a whole year’s worth of monitoring data has been compiled and analysed, from December 2020 to November 2021.
“The current study suggests that relocating corals from coastal development sites, where habitat loss is unavoidable, could be considered a tool that will aid in the conservation of urban reefs,” the study notes. A researcher associated with the exercise, who did not wish to be identified, said, “This proves untrue what many experts, including marine biologists, were saying about the coral’s chances of survival. I am not commenting on the merits of the Coastal Road project, but this exercise has shown that reef-building corals around Mumbai are very resilient. It may help in conserving other coral populations along with the Maharashtra and western Indian coast, such as in the Malvan Marine Sanctuary.”
This view was echoed by Virendra Tiwari, additional principal chief conservator of forests, and mangrove cell. “The work of translocation of corals was carried out under the supervision of the Mangrove Cell and we are happy that it has succeeded. The site of relocation, Navy Nagar, is well protected due to restrictive entry. This exercise has the potential to become a model for translocation of corals in and around the Konkan, as the data collected over one whole year shows.”
However, NIO’s research also highlights prominent threats to this ecosystem, including contact with marine debris, coral bleaching and sediment smothering, and algal growth. In August and September 2021, almost 95% of the total coral colonies were found to have been subject to bleaching. Nearly all were found to recover from the bleaching incidents after the passage of the monsoon.
Coral bleaching is how corals lose their vibrant colours, which are imparted by microscopic algae called zooxanthellae. These share a symbiotic relationship with the coral, which provides the algae with an optimal environment for photosynthesis. The algae produce oxygen and nutrients which are shared with the host. This relationship is typical to nearly all hermatypic (or reef-building) corals.
When placed under stressful conditions, such as exposure to pollutants, changing salinity levels, or rising temperatures in the form of marine heatwaves, the coral expels its algae and loses colour. Not all bleached corals die, but they do become prone to mortality and disease.
While there has been considerable research on coral ecosystems globally, and even in India (in the Gulf of Mannar, Andaman and Nicobar Islands, Lakshadweep Islands, and the Gulf of Kutch), there has been a dearth of studies on the patchier distribution of reef-forming corals along the eastern coast of the Arabian Sea. “This leaves out a huge gap in our understanding of their current ecological status and potential threats to their wellbeing. That’s why this study is important,” said the researcher cited above.