The COVID-19 lockdown has had a positive impact on the coastal ecosystems of the Gulf of Mannar along Thoothukudi district.

Limited industrial activities and human interference has reduced the levels of pollution, increased the number of fish species and density and has improved the overall quality of marine water, reveal findings by the Suganthi Devadason Marine Research Institute (SDMRI) in Thoothukudi.

Director of SDMRI, J.K. Patterson, says that while collecting data for a State government project, the institute conducted a study between May 25 and June 2 to assess the level of plastic pollution during the lockdown along the coast of Thoothukudi district.

There has been a remarkable reduction in the macro and meso-plastic pollution levels at eight locations along the coast -- Manapad, Tiruchendur, Thoothukudi Harbour beach, Inigo Nagar, Muthunagar beach, Therespuram, Vellapatti and Tharuvaikulam. The average reduction in the level of macro-plastic is 51.4% and that of meso-plastic is 28%.

Plastic spoons constituted the highest quantity of plastic that was found, followed by plastic cups. “This reduction in plastic pollution levels can be attributed to the absence of movement of people along the coast, as before the lockdown, a large number of people used to throng pilgrimage and tourist destinations at these locations. This is also a significant outcome as plastic pollution threatens the existence of marine biodiversity and can enter the human food chain,” says Mr. Patterson.

Another major outcome of the study is the increase in the number of species of coral reef fishes from 89 in February to 96 in May, at the Thoothukudi group of islands of Gulf of Mannar -- Vaan, Koswari, Kariyachalli and Vilanguchali. The average fish density has also increased by 22%.

“Generally, fish tend to migrate in the summer due to high temperatures. But, despite the high water temperature due to climate changes and subsequent coral bleaching this summer, the fish population has increased, thanks to less human disturbance during the lockdown period,” he says.

Usually, more than 300 fish-traps are illegally deployed every day to collect reef fishes like Scarus, Lutjanus, Lethrinus and Siganus. These species are highly exploited as they command high commercial value in the market, he adds. Fortunately, due to the absence of trap-fishing and reduced human intervention during the lockdown period, the population of Scarus ghobban (parrot fish), has increased by 39%.

“The Scarus ghobban, a herbivorous reef fish that feeds on seaweeds, plays a highly significant role in maintaining the ecological balance in the coral ecosystem. The increase of herbivore fish population between April-June 2020, is expected to increase the coral cover,” he says.

Also, a study conducted to assess the quality of water at stressed locations -- Therespuram, Roche Park and Thoothukudi Port -- showed that there is an increase in dissolved oxygen levels and a significant decrease in concentration of metal and microbial concentrations.

“Thus, the lockdown has brought about a considerable positive change in the coastal ecosystems, which will help in the conservation of biodiversity. These findings encourage us to protect the coastal ecosystem in the post-lockdown period too,” he says.