Tamil Nadu to field local warrior to wage ‘biowar’ on invasive Kakka Aazhi species

CHENNAI: In their desperate battle against Kakka Aazhi, the aggressively invasive mussel species that has colonised Kosasthalaiyar river's ecosystem, the experts here have decided to turn it into a ‘biological war’ of sorts: use whelk (or kadal nathai as it is called locally), a gastropod found in abundance in Pulicat lake, which may be able to stymie the foreign invader.

Speaking to DT Next, Deepak Srivastava, member-secretary of Tamil Nadu State Wetland Authority (TNSWA), said whelk (Rapana Rapiformis) is found to be able to control Kakka Aazhi under laboratory conditions.

"The whelk gastropod has been used under laboratory conditions, which we need to try out in field conditions as a biological control measure for Mytella Strigata (the scientific name of Kakka Aazhi). This is based on inputs from the Central Marine Fisheries Research Institute (CMFRI)," he said.

He added that Rapana Rapiformis is present in Pulicat lake and sea ranching (the process under which they are raised in a controlled environment and then released in selected area) of Rapana Rapiformis and Rapana Bulbosa, another gastropod, may work. "We need to try it in selectively dredged portions in order to have an impact on charru mussels," he added.

The attempt is being considered based on instructions given by Chief Secretary N Muruganandam. During a meeting convened a few days ago to discuss the invasion of Kakka Aazhi, it was apprised that the National Institute of Ocean Technology (NIOT) has given a proposal to use chemicals to control the invasive mussel.

However, as using chemicals could affect the aquatic ecosystem in the river, the Central Marine Fisheries Research Institute (CMFRI) was asked to submit a proposal for biological control of the mussel. Experts from the institute explained that the biological control method would yield desired results only in the dredged area because the mussel’s multiplication rate is very high and any attempt to biologically control the species without dredging would be a wasteful exercise.

Based on the discussions, Muruganandam directed the Water Resources Department (WRD) to start dredging in Kattupalli, Puzhuthivakkam, and Athipattu areas (1.7 km of the river) as per the directions of National Green Tribunal (Southern Zone) and conduct a quick baseline study to measure the impact along with TNSWA. Directions were also issued to carry out biological control measures in dredged areas.

Meanwhile, TNSWA member-secretary Srivastava informed the tribunal that unlike any other measures under consideration, the biological control of Mytella Strigata would be a long-term solution to control the spread, which has never been attempted in Tamil Nadu.

"Keeping in view the rapid multiplication of the Mytella Strigata, the biological control method shall be implemented on pilot basis in the selectively dredged area and the effectiveness of biological control shall also be validated during this pilot study, " the report submitted to the tribunal said.

A joint inspection was conducted by the officials of Tamil Nadu Wetlands Mission, WRD, National Centre for Sustainable Coastal Management (NCSCM), Dr MGR Fisheries College, and Dr J Jayalalithaa Fisheries University along with local fishermen on November 21 along the 1.7 km stretch which is proposed to be dredged.

The WRD has informed the team that the formation of pit work was progressing, and that a dredger has been deployed in Kosasthalaiyar backwater and the dredging would commence in a full-fledged manner soon.

In October, the NGT directed the government to engage more men and machines to remove the invasive species. The Tamil Nadu government blames Ennore Port, Chennai Port, and Kattupalli Port for the invasion, claiming that ballast water from these facilities was the possible source.