May 7, 2009

Source of Massive Bloom Discovered

The origin of the massive green tide of algae that nearly wrecked the Beijing Olympics sailing regatta has been discovered by scientists, BBC news reported Wednesday. 

Satellite images divulge evidence that swift development of farmed seaweed nearly 200km down the coast is the cause for the colossal algal bloom.

As the green tide drifted closer to the regatta city of Qingdao, it multiplied in size, so much so that it is regarded the largest ever recorded in the entire world. 

It was proposed by the international media and many scientists, in the beginning, that a surplus of nutrients (eutrophication) in the waters along the coast created the algal bloom. 

However, a recent publication in Marine Pollution Bulletin discusses a new finding that rejects the theory and even suggests that comparable tides could occur again. 

In late June 2008, the Qingdao venue hosting the Olympic sailing regatta experienced an enormous green tide blanketing over 600 sq km in the waters and along the shoreline.  With the help of more than 10,000 people, one million tons of algae were extracted from the beach and coast over a little more than a two week span. 

The species of algae causing this disruption is termed Enteromorpha prolifera.

"It's not a dominant or common species in the local area," informs Dongyan Liu, a marine biologist at the Chinese Academy of Sciences in Yantai, Shandong.
"The rapid appearance and sheer scale made us suspect it had accumulated offshore and been transported in."

Farms that cultivate Porphyra seaweed on partially floating rafts made of bamboo and net curtain are polluted by E. prolifera.

Typically, the seaweed is grown to be sold as food and additionally to prevent eutrophication.  It works for this purpose by consuming nutrients that might otherwise pollute the water, permitting weeds to grow and depriving other plants of oxygen. 

Liu and Keesing of the Australian research organization CSIRO received photos that revealed the Qingdao green tide had bamboo poles utilized for Porphyra aquaculture within it. 

The researchers then questioned farmers across the Yellow Sea along the coast of the Jianngsu province who were also growing seaweed.  According to their harvest schedule, it is possible the bloom could have originated there. 

To explore further, Liu, Keesing and team reviewed photos of China's north-eastern coast captured by instruments on board Nasa's Terra and Aqua satellites, which look over the Earth's surface completely every one to two days. 

The images of May 15, 2008 depicted small green patches of algae in an area of 80 sq km appearing off the coasts of Yancheng and Lianyungang in Jianngsu province.

Just ten days later, the green patches migrated away from the coast and into the Yellow Sea, covering 1,200 sq km, and impacting about 40,000 sq km of ocean.

Algae patches started moving closer to the coast at Qingdao on June 18, and finally reaching shore on June 28. 

Further evidence to support these new suggestions were confirmed by satellite data that revealed favorable temperatures, wind speeds and oceanographic conditions were present at the time to promote the quick growth of the algae, and carry it across the Yellow Sea. 

"We suspect that the reason the bloom had not occurred previously was that the growth of aquaculture in this region has been so rapid," said Keesing.

The coastal area reserved for seaweed aquaculture off the coast of Jianngsu has more than doubled to 23,000 hectares from 2003 to 2008.

"It has now reached a critical size where it has the capacity to produce enough Enteromorpha to cause the problems we saw in 2008," the CSIRO researcher said.
To prevent a reoccurrence "we should carefully manage the distribution and production of coastal aquaculture and educate farmers not to discard unwanted Enteromorpha into the water."

Image Courtesy EarthFirst


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