Scientists identify causative species of algal bloom.
The species of alga that causes 'brown tides' in the United States and South Africa is also to blame for massive blooms along China’s east coast on the Bohai Sea, researchers have found.
“The identification of the causative agent is the first step towards tackling the problem,” says Christopher Gobler, a marine ecologist at Stony Brook University in New York.
In June 2009, routine monitoring by China’s State Oceanic Administration (SOA) picked up some brown discolouration in waters with high concentrations of algal growth off the coast of Hebei province. At the same time, cultivated scallops, oysters and mussels in the region — the largest shellfish production site in the country — began to die off.
The situation got worse the following summer: 3,350 square kilometres of waters were affected and Hebei was hit by 205 million renminbi (US$32.1 million) in direct economic losses, according to the SOA’s annual report on marine disasters.
The bloom reappeared in May for the fourth consecutive year, and has spread farther south, reaching the coast of Shandong province.
When Ren-cheng Yu, a marine ecologist at the Chinese Academy of Sciences’ Institute of Oceanology in Qingdao, Shandong province, and his colleagues were called in to investigate the incident three years ago, they realized that this was a type of algal bloom that had never before hit China.
"The blooms are extremely dense," says Yu, "with billions of algal cells in every litre of seawater." They are also very toxic to coastal ecosystems, he says. The findings are published in the journal Harmful Algae1.
By assessing the size of the cells and the types of pigments they contain, the researchers were able to narrow down the hunt to half a dozen species. Genetic analyses then led them to conclude that the causative agent is Aureococcus anophagefferens, the species that causes brown tides in the United States and South Africa2. The researchers are looking into why shellfish are so vulnerable to this species.
In addition to killing shellfish, brown tides affect other aspects of coastal ecosystems, says Mingjiang Zhou, a marine ecologist also at the Qingdao institute. They make the water dark and turbid, which slows the growth of the sea grasses that provide an important habitat for juvenile shellfish and fin fish.
The team is now trying to pin down what caused the brown tide in China, and whether the alga is native or came from shellfish introduced from the United States. “It’s still too early to tell,” says Zhou. But he suspects that the blooms are related to the country’s deteriorating coastal environment.
In the past few decades, China’s rapid pace of population growth and agriculture development has led to more nutrients being discharged into the sea — in the form of sewage, animal manure and fertilizers. That excess has caused massive algal blooms since the 1990s, especially at the Yangtze estuary. Those blooms have had a red or green hue, known as red or green tides, because of the pigments of the algal species responsible.
“The recent brown-tide outbreaks may be the latest manifestation of increasing nutrient loads in China’s coastal waters,” says Gobler.“There isn’t much we can do once the bloom hits,” says Yu. As an emergency measure, the researchers are pouring modified clays into affected waters to absorb and remove the alga. But “it’s not very effective because of the sheer number of cells”, he says. The researchers hope that their work will lead to molecular tools for early detection as well as ways to slow down or even disrupt growth of the alga.
In the meantime, researchers say, the government should step up its efforts to reduce the flow of nutrients into the sea and to restore the quality of coastal waters. “This is key to protecting both aquaculture and natural marine ecosystems,” says Zhou.
Zhang, Q. et al. Harmful Algae http://dx.doi.org/10.1016/j.hal.2012.06.007 (2012).
Gobler, C. et al. Proc. Natl Acad. Sci. USA. 108, 4352-4357 (2011).
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Qiu, J. China third country to be hit by ‘brown tide’. Nature (2012). https://doi.org/10.1038/nature.2012.11015