SRI LANKA Trincomalee, fish die from excessive concentration of algae

The phenomenon, already recorded in other places, occurred for the first time in the port city where the Mahaweli River flows. The affected species is the odonus niger, which is found decomposing in shallow bays. Dr Sujeewa Athukoorala: “Oxygen deficiency and gill obstruction.” Scientists: algae proliferation favored by “sunlight, hot water, carbon dioxide and fertilizers.”

Trincomalee () – A nauseating smell has invaded Trincomalee, a port and tourist city, center of Tamil culture, located on the northeastern coast of Sri Lanka. It was caused by the presence of thousands of decaying fish that washed ashore and floated in shallow bays. It occurred between October 29 and November 1, coinciding with Halloween week, which unleashed rumors of unlikely supernatural events among tourists and residents. The affected species were mainly the red-toothed triggerfish (odonus niger), named for its characteristic red teeth visible when its mouth is closed.

According to Dr Sujeewa Athukoorala, a scientist at the National Aquatic Resources Research and Development Agency (NARA) in Colombo, “satellite images from the affected period indicate a high-density algae bloom in the waters of Trincomalee.” The phenomenon, recognizable by the change in water color, “probably caused a shortage of oxygen in the fish’s habitat, as dense algae can clog the gills of the triggerfish, making it difficult for it to breathe. “Thus, the combination of low oxygen and gill obstruction may have caused the mass death of the triggerfish.”

Academics Nishantha Adikari and Anuradha Dissanayake told that “Sri Lanka experienced heavy rains throughout October and the Mahaweli River (the longest in the country, ed.), which empties into the sea in Trincomalee, would have transported large volumes of water sweetness and nutrients to the marine environment. During heavy rains, excess nutrients are washed out to sea and could trigger algae blooms. “Studies have revealed that there are four main causes of algae blooms: sunlight, warm water, carbon dioxide and fertilizers. “When these four factors are at appropriate levels, algae have the ability to double their mass every six hours.”

Once the amount of nutrients is high, a harmful level of algae growth is reached and, at that point, the fish in the water cannot find their usual food and the plants on the bottom begin to die due to the lack of sunlight that It causes thick floating mats of decaying algae to form on the surface, further damaging the ecosystem. At this point, the water runs out of oxygen and becomes a “dead zone” that kills fish and most other organisms. “As the algae decompose, phosphorus is released into the water and flows downstream, where it can trigger other algal blooms. Finally, phosphorus reaches coastal wetlands. About 90% of ocean life depends on a coastal wetland,” explain Nishantha and Anuradha.

According to environmentalists Joseph Aruliah and Stephen Ravichandrarajah, residents of Trincomalee, “a similar situation has occurred in the Maldives: several cases of dead fish stranded in large quantities on the coasts of the northern atolls in September 2023.” But this is the first time such an incident has occurred in Trincomalee and therefore “there is a need for NARA to carry out a long-term investigative study to find out the cause.”

“Occasionally, cases of fish deaths are also observed in India. In most cases, this occurs due to complications arising from high temperatures. In most of these cases, a combination of natural and unnatural causes triggered the recent increase in fish deaths, and more often than not, the fish were in a state of pure physical exhaustion, which ultimately led to their death. death. «Recent research indicates that increased fish mortality is the result of several factors, including reduced water purity and quality. Studies also point to India, China, Kenya and the United States as countries that have experienced an increase in fish mortality,” they conclude.