SINGAPORE – The world is on alert for microscopic sea algae that can multiply and suffocate seas, causing swathes of the ocean to change color and thousands of dead fish on the surface.

This ocean hazard – called harmful algae blooms – is a global phenomenon that is increasing alongside increases in fishing, coastal development and marine exploitation, according to a groundbreaking United Nations (UN) study.

More than 9,500 blooms have been reported worldwide over the past 33 years, according to a study conducted by the Intergovernmental Oceanographic Commission of Unesco.

Although harmful algal bloom events have increased in some regions, there have been no significant changes in Southeast Asia as the number of events remains stable.

But aquaculture – a key cause of algal blooms – increased 16-fold between 1985 and 2018, with the largest increases seen in Southeast Asia and South and Central America.

The seven-year study by 109 scientists, published in Nature’s Communications Earth & Environment on Tuesday, June 8, said the increase in coastal fish farms has been a key factor in the dire economic impacts of harmful algal blooms.

Such blooms are mainly caused by changing hydrological and environmental conditions, such as precipitation regimes and nutrient loading into the seas.

In fish farms, fish feed and waste are additional forms of nutrients released into the sea. Microalgae devour the nutrients and multiply greatly, ultimately causing the fish to die from lack of oxygen.

Certain algae, armed with “weapons”, can also damage the gills of fish.

Some microalgae produce toxins that can cause serious health problems and poisoning in humans if they eat sick seafood.

Singapore – an island state with its coasts bustling with fish farms, water treatment plants and land reclamation, has not been spared from harmful algal blooms.

In mid-January, residents of Sentosa Cove were stunned to see a generally pristine stream turning pinkish-purple. A week earlier, crowds of dead fish were seen near the banks.

A 2021 local review document on Harmful Algal Blooms and Aquaculture identified 22 events reported between 1987 and 2017. Most occurred in the Strait of Johor to the north where most of the most of 100 fish farms on the island.

There are several reasons why the Strait is susceptible to harmful algal blooms. For example, a 2014 study published in the Raffles Bulletin of Zoology noted that seasonal monsoons can change the salinity of water, which in turn affects the growth of microalgae. Maritime and industrial activities also lead to discharges and turbulent waters.

The Singapore Food Agency (SFA) will study the impact of fish farming on the water quality of the Eastern Strait of Johor, in order to minimize and mitigate events such as algae blooms and bacteria that affect fish health.

In the future, climate change will also increase the frequency and severity of harmful algal blooms.

According to the United States Environmental Protection Agency, when the ocean warms, surface water stays at the top because it is less dense. This means surface waters will not mix properly and algae will grow thicker and faster, robbing oxygen from other marine life and blocking their sunlight.

“Climate change, anthropogenic impacts and environmental impacts contribute to this phenomenon all over the world, and it is impossible for you to have less algal blooms unless you stop dumping nutrients into the water. . And I don’t see that happening right away, “said associate professor Federico Lauro of the Asian School of the Environment at Nanyang Technological University.

However, the UN study noted that at this point, the widely held view that harmful algal blooms are on the increase around the world, possibly due to climate change, is not. confirmed.

Dr Adriana Zingone, one of the authors of the UN study from the Italian research institute Stazione Zoologica Anton Dohrn, told the Straits Times: “The more we have to exploit marine resources, the more we will detect new ones. Harmful algal blooms, including those that may have occurred earlier but had never been noticed due to lack of studies or human activities in this area. “

Lead author of the study, Professor Gustaaf Hallegraeff of the University of Tasmania, said the intensification of aquaculture has led to increased efforts to monitor algal blooms, which is crucial to support industry and protect human health.

In Singapore, aquaculture is here to stay as it is part of the nation’s vision to produce 30 percent of its nutritional needs to enhance food security.

The SFA encourages offshore fish farms to minimize the impact of blooms and other environmental problems by adopting high-tech farming methods. One of these methods is to recirculate aquaculture systems in closed fish farms, where seawater is constantly reused and virtually no waste is released.

The UN study also created the world’s first database of harmful algal blooms, so scientists can track their locations, frequency and impact across the world, and how climate change could. modify the phenomenon.

Researchers in the study also hope the article will spark more investigations into algal blooms in each country.

“Our study will hopefully stimulate site-by-site studies to clarify local trends, which after all are the ones that really matter,” said Dr Zingone.