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[BEIJING] 'Red tides' — outbreaks of toxic algae — are on the increase in China, where scientists are looking to use clay to curb small-scale occurrences.

Yu Zhiming, senior research fellow of the Institute of Oceanology, Chinese Academy of Sciences, is developing a new type of clay that causes the algae to lose its vigour and limits its reproductive capacities without damaging the ocean. So far, the clay has been tested in sea farms to prevent the spread of red tide-causing algae.

Clay helps eliminate red tides by forming clumps around the suspended algae, making it sink to the sea floor. According to Yu, it can also be used to form a 'vacuum belt' to prevent further invasion of red tides. He admits, however, that the method is too costly and technically difficult to prevent and terminate massive red tides, whose threat in China has been increasing in recent years.

In 2003, China was hit by red tides 119 times, 40 times more than in 2002. Approximately 14,000 square kilometres were affected, devastating marine life, contaminating fish stock and causing economic losses of more than US$5 million. According to an official from the State Oceanic Administration, the increasing incidence of red tides is caused by rising pollution discharged into Chinese seawater in recent years.

However, Yu says that scientists have not found the statistical link between pollution, sea climate, habits of algae and the occurrence of red tides.

Yu's team is studying a type of algae that is responsible for red tides off China's shore. They have traced its distribution and its relationship to warm ocean currents and are studying links between ocean water stability and the occurrence of red tides. Yu hopes their work will become a base for scientists to predict the occurrence, scale and toxicity of red tides in the future.

Although clays offer good promise, he says the fundamental solution would be to control and reduce pollution discharge into the sea.

South Korea and Japan already rely on spraying clay over expanses of seawater to control red tides. South Korea says the method helped reduce red tide-related fisheries loss from US$10 million in 1995 to US$1 million in 1996.

But researchers elsewhere are concerned over the potential environmental effects of spraying vast quantities of clay into the ocean. Some worry that the clay might smother other forms of life on the sea bed, and point out that they remain unsure of what happens to the algae once it has sunk.

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