NANJING, Jiangsu Province: Among the major seas in China, the East China Sea was the worst hit by the red tide in 2005, according to the 2005 China Marine Environment Quality Bulletin released by the State Oceanic Administration (SOA).

Red tide refers to reddish discolouration of coastal ocean waters caused by a bloom of dinoflagellates a certain marine plankton species. Certain dinoflagellates produce toxins that can kill fish and contaminate shellfish, explained Zhou Minjiang, researcher with the Marine Science Research Institute under the Chinese Academy of Sciences.

According to Zhou, eutrophication due to an unbalanced ratio of nitrogen and phosphorus in the seawater is the main cause for red tide. Eutrophication is a process where water bodies receive excess nutrients that stimulate excessive plant growth.

Statistics from the SOA bulletin show that the East China Sea witnessed 61 per cent of a total of 453 red tides in China between 2001 and 2005.

Also, according to the bulletin, large-scale red tides are more likely to visit the East China Sea.

During the past five years, among 132 red tide occurrences which covered more than 100 square kilometres each, and 33 red tide occurrences which covered 1,000 square kilometres each, most tended to swamp the areas adjacent to the Yangtze River estuary and the marine area south of Zhejiang Province.

Among the several provinces and municipalities along the East China Sea coast, Zhejiang Province is the most seriously hit by red tide.

Statistics from the SOA show that among the 453 red tides from 2001 to 2005, 38 per cent hit Zhejiang. Red-tide-influenced sea area near the province has amounted to 56,890 square metres.

SOA marine surveillance also found that large-scale toxic red tide, poisonous to fishery products and human health, frequently occurred in the East China Sea area near Zhejiang and Fujian provinces.

A sea area of 7,000 square kilometres in Zhejiang was invaded by toxic red tide during the months of May and June 2005.

"But due to effective measures taken by the SOA and local governments, no case of poisoning was reported during that toxic red tide period," said SOA spokesman Li Chunxian, in advance of the 14th World Water Day on March 22.

In addition to Zhejiang, neighbouring Jiangsu Province has also witnessed increasingly severe red tide invasions in recent years.

According to statistics from Jiangsu Provincial Marine and Fishery Bureau, red tide attacked the province's coastline four times last year, covering an area of 1,275 square kilometres, 12 times larger than that of 2004.

May and June used to be the major periods for red tide. But recently, this East China province has seen severe occurrences in winter.

Local authorities are working steadily to establish an effective emergency response mechanism to fight the unpredictable red tide.

While it was often regarded as a natural phenomenon triggered by changes in seawater temperature, salinity and sunlight, some researchers have found that red tide is also an outcome of coastal pollution by extensive sewage discharge containing nitrogen and phosphorus.

"With fast economic development, industrial discharge from factories in the well-off East China provinces have contaminated seawater severely in recent years. This is a reason why red tide occurs more frequently in the East China Sea," said Chen Feizhou, a researcher with Nanjing Institute of Geography and Limnology.

Monitoring zones

In a bid to curb and control red tide, nine monitoring zones have been established in the East China Sea area.

According to statistics from the East China Sea Bureau of the SOA, a monitoring zone, usually possessing at least six regular stations, conducts daily monitoring and also has laboratories on microbiology, fish disease pathology and biological toxicity.

The zone can monitor water quality, biology and weather in the area.

When red tide occurs, an emergency mechanism will be launched immediately and corresponding measures will be implemented to help reduce damage.

In addition, volunteers among local fishermen have been encouraged to join in the red tide emergency mechanism in order to get more first-hand detailed information.

Greater attention will be paid to quality checks of fishery products from areas under the influence of red tide, in order to guarantee food security, according to the report.

"As red tide is challenging the marine environment, the best thing we can do is to gather information, respond in time and minimize damage," according to Chen.

China reported 82 occurrences of red tide in 2005, a decrease of 15 per cent compared with the previous year, according to the SOA bulletin.

Areas hit by red tide last year added up to 27,070 square kilometres, the same as in 2004, according to the report.

However, toxic algae triggered a total of 38 occurrences of red tide last year, affecting a total area of 14,930 square kilometres, representing a sharp increase in both the number of occurrence and affected area.

The country currently has established 33 red tide monitoring zones in related sea areas.

Also, monitoring results indicate that China faces severe pollution of inshore maritime territory, as 139,000 square kilometres of China's maritime territory were below seawater quality standards for clean sea areas in 2005, according to the SOA bulletin.

(China Daily 03/13/2006 page8)