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[MANILA] Local clay could help control the harmful algal blooms that destroy fish catch in the Philippines, according to researchers.

Scientists at the University of the Philippines' Marine Science Institute found that the blooms — commonly known as red tide — can be mitigated by spraying 'ball clay', which binds to the algae.

Ball clays are tiny, powdery clay particles commonly used in pottery and ceramics manufacturing. They are cheap and readily available in the Philippines.

The clay particles stick to the algae and sink them within minutes. Any algae that survive the journey to the bottom of the sea die after being deprived of sunlight, said project co-leader Rhodora V. Azanza.

Red tide can seriously affect fish catch and eating infected organisms, such as shellfish, can result in poisoning and death. It occurs in waters around the world and researchers are still pinning down the exact causes, and ways of predicting and preventing its occurrence.

"Algal blooms are a normal phenomenon. What is alarming is that they have become more frequent, especially [those with] toxic species," said project-co-leader Maria Lourdes San Diego-McGlone.

"Ball clay is used with seawater to form a slurry," McGlone said, adding that mixing it with seawater improves its effectiveness.

The technique, devised in collaboration with engineers, was tested successfully earlier this year in a bloom of Pyrodinium algae — the key red tide species affecting the Philippines.

No negative effects on other marine organisms were observed, but the researchers are still conducting experiments to test for longer-term effects.

They hope the method could be used in other parts of the world, adding that using clay is better for the environment than, for example, using chemical compounds and biological algae control.

Sandra Victoria Arcamo, a resource management specialist at the Bureau of Fisheries and Aquatic Resources, welcomed the initiative but called for a more integrated approach, which would include coastal clean-ups and public education.

Donald Anderson, a senior scientist at the Woods Hole Oceanographic Institution, United States, said that these types of interventions are site-specific because both the harmful algae and the clay come in many different forms.

"You have to tailor a particular clay to each organism," he said.

He also warned that the method could be harmful to "environments where clay is not natural, such as coral reefs".

But Anderson added that clay "keeps rising to the top as an effective, relatively cheap option" for red tide control. "Clay mitigation is extremely benign when compared with red tide effects."

Additional reporting by Jan Piotrowski.