Extreme plankton bloom in Thailand threatens marine life, fisheries

While marine animals such as fish and whales eat plankton, it can also prove toxic in large amounts. When a bloom occurs, it starves the ocean of oxygen, killing fish, shellfish and other creatures, which creates chaos in the natural food chain as well as fisheries.

“This is the first time that I've seen this much (plankton) since I was born, which means it is very severe this year," says marine scientist Tanuspong Pokavanich, as he passes by a dead sea eel floating on the water's surface during a field trip to collect water samples along the Chonburi coastline.

Of the currently affected area, which Tanuspong and his team estimate to be about a quarter of Thailand's Upper Gulf, about half appears green, while the other half closer to shore has turned brown, from pollution and dead plankton, the scientist says.

“The plankton in the water will (either) consume all the nutrients and thrive, or they will die due to a lack of light. Their carcasses will then sink to the seabed and decompose," says Tanuspong.

The process of decay causes low oxygen conditions in the water and that too affects marine life.

Floating along the coastline are more than 260 mussel farming plots, of which over 80% have already been severely impacted by the bloom, according to an authority from the Chonburi Fisheries Association.

Department of Fisheries data from 2021 shows Chonburi can produce 2,086 tonnes (4.6 million lbs) of mussels per year worth 26,655,000 THB ($1 million).

“The damage appears to be 100 %. See, they just fall off when you shake it. There are no live ones left, they're all dead, including the oysters too. Normally, they would cling (to the rope) here," 47-year-old local fisherman Suchat Buawat, who owns over 10 farming plots, told Reuters as he inspected his dead shellfish.

With the bloom impacting the quality and quantity of his mussel harvest, the fisherman of over 20 years in Chonburi's Si Racha district estimates his losses to be over 500,000 baht ($14,000).

While the exact cause behind the green seawater is yet to be determined, scientists like Tanuspong are exploring potential links to climate change and natural weather patterns like El Niño to help those whose livelihoods depend on the sea.

The discovery that the current plankton bloom is dominated by the Noctiluca species — the same species that was initially thought to be inactive but which returned during the El Nino in 2019/2020 — prompted Tanuspong and his team to study whether there is any link between the two occurrences.

He hopes the data and their findings can be used to forecast future plankton blooms, allowing fishermen to predict the best times to farm and harvest.

But science alone will not mitigate the consequences of blooms, says Tanuspong. "If we don't start contributing (to conserve the Earth), nothing will change."

Worldwide, marine heatwaves have become a growing concern this year, with thousands of dead fish washing up on beaches in Texas and experts warning of algal blooms along the British coast as a result of rising sea temperatures.

Reuters