Many people may have tasted mala xiaolongxia - crayfish cooked in very hot spices - particularly in Beijing where the dish has become very popular.

But few will know that the crustacean, which resembles a miniature lobster, is an alien, invasive species introduced into China during the 1930s from Japan. Its original habitat is in North America.

Crayfish, which breed and grow rapidly, pose a great threat to aquatic life in those waters it inhabits. It can also weaken dams because it bores caves in them.

During the Yangtze River flood in 1998, workers found that the species was responsible for a large number of breaches in dams along the river.

In the Dongting Lake Nature Reserve in central China's Hunan Province, experts from the reserve, Peking University and the Chinese Academy of Sciences have begun to look for ways to curb the spread of the creature, the People's Daily reported on May 29.

The crayfish highlights the dangers to indigenous species by the introduction of alien specimens.

Wang Dehui, deputy director of the Department of Natural Environment Conservation under the State Environmental Protection Administration, described the problem of alien invasive species in China as "serious."

He said such species pose a threat to the biodiversity, forestry and agriculture of China.

Experts estimate that economic losses caused by them cost the country more than 50 billion yuan (US$6 billion) each year.

According to Cai Lei of the co-ordination office for implementing the Convention on Biological Diversity under the administration, half of the 100 malignant invasive species listed by the World Conservation Union (IUCN) in 2001 have found their way into China.

With the exception of some remote areas on the Qinghai-Tibet Plateau, all the 34 provinces, municipalities and autonomous regions are affected.

Their impact can be devastating. Each year the area of forests damaged by invasive insects, such as the American White Moth, totals 1.5 million hectares.

It is difficult to halt the damage caused by invasive species, because once introduced they enter the natural environment where they become difficult to eliminate, said Cai.

Many experts warn that the impact of a number of alien invasive species on biodiversity can take between five to 20 years to emerge. Therefore, prevention must be the top priority for protecting indigenous fauna and flora, she added.

The administration is currently co-operating with relevant departments to establish a mechanism for the prevention and control of alien invasive species, said Cai. This will include new laws, a system for evaluating the danger of invasive species and a monitoring system.

In addition the country will keep lists of those species already in China and publicize them so that policy makers at all levels and also the general public can help prevent and control the species, she said.

(China Daily June 18, 2003)