UP researchers confirm foreign studies showing clay can control red tide

Researchers from the University of the Philippines’ Marine Science Institute have confirmed earlier foreign studies that clay can control red tide, which frequently occur in Philippine waters and adversely affect the country’s fish supply and sometimes cause deaths.

Dr. Rhodora Azanza and researchers from UP-MSI have tested a technique developed by South Korean scientists using a ball of clay to control Pyrodinium bahamense var. compressum or the toxic red tide-causing organism.

The researchers found that at 0.5 gram of clay per liter of water, the population of the organism suspended in the water went down from 95 percent to 51 percent, the Department of Science and Technology (DOST) reported.

“The clay particles flocculate or band the suspended organisms together in the water and settle them at the sea bottom where it becomes inactive. No significant negative effects on water quality and marine life have been reported,” the DOST said.

In South Korea, researchers at the National Fisheries Research and Development Institute found that application of eight grams of clay per liter of water in red tide-stricken waters effectively reduces by 80 percent the populations of the dinoflagellate Cochlodinium Yolykrikoides, the DOST said.

“This type of red tide can cause fish kills at high densities,” it said.

Based on research, the use of clay to control red tide is a widespread practice in South Korea to protect the region’s fish farming industry.

Red tide is a term used to describe all phenomena in which the water is discolored by high algal biomass or concentration of algae, the Department of Agriculture’s Bureau of Fisheries and Aquatic Resources said.

“The discoloration may not necessarily be red in color but it may also appear yellow, brown, green, blue or milky, depending on the organisms involved. It may either be harmful or harmless,” it said.

Harmful algal bloom (HAB) is a term used to describe events associated with the blooms of algae, which cause harmful effects to the environment, living organisms and humans.

BFAR said harmful algal blooms have adverse effects on marine resources, human health and economy of the country.

Between 1983 and 2002, a total of 2,122 paralytic shellfish poisoning (PSP) cases with 117 deaths affecting all age groups have been reported, it said. – Helen Flores