A large, drifting algal bloom that has left 3,500 fish dead along a 10km stretch in Ramanathapuram district has prompted scientists from the Central Marine Fisheries Research Institute (CMFRI) to take help from eyes in the sky to monitor the algal bloom’s path.
The shoreline between Kunthukal in Pamban and Vedalai in the Gulf of Mannar turned green on Thursday, resulting in the death of at least 3,000 fish. On Wednesday, local fishermen reportedly found 500 fish lying dead on the coast. An algal bloom is the rapid growth of microscopic algae that form a green cover over water bodies blocking the sunlight.
“We are continuously monitoring the situation - from both the field and using satellite images to analyse the extent of the algal bloom,” says the scientist-in-charge in Ramanathapuram for CMFRI R. Jayakumar. The scientists will look at the bloom's size, its path and how far it is from the coast, and analyse how long it will take to dissipate. The primary cause of death of fish is algal choking as well as ammonia poisoning that algae excrete. “The bloom seems to be moving south towards the Palk Strait - which is another 2-3km south from here,” he adds.
The bloom of algae is a death knell for fish as it is not just a sign of increased temperatures and pollution, the algae also excrete ammonia, depletes the water of its oxygen and even physically chokes fish - like in the case of Ramanathapuram.
Increased temperature, abundant nutrients, low tidal amplitude, and low currents have given ideal conditions for algae to bloom at this point of the year. The difference between the high tide line and the low tide line is not very big, which means there is less water movement. “Without currents or tidal activity, the water is not flushing out the algae. But this is not a long-term problem. With rains on Thursday night and a cooler temperature, we expect the bloom to dissipate soon,” says Jayakumar, adding that the last time this happened was five years back.
Last month, a similar algal bloom caught the fancy of beach-goers in Chennai. Though it did not leave any fish dead in the city, the glow of the bioluminescent algae led to a bloom in social media posts. Marine researchers at that time said that the bloom had travelled more than 30km before it reached Chennai.
