First report of Ferrissia wautieri and Physa acuta in Taihu Lake of China

As humans increase the speed and frequency of global travel and move more materials across international boundaries, the immigrations of organisms increase dramatically through the human agency. Humans have created a world without borders for many species^[1] and rates of human-caused species invasions are far greater than the rates that would have occurred naturally^[2]. The snail species Ferrissia wautieri MIROLLI 1960 and Physa acuta DRAPARNAUD 1805 are known to have spread in many countries as invasive species^[3]. However, until now, there are no reports about these species threatening native communities, as it is known from several other invasive species. So far, there has been still lack adequate knowledge on invasive species in China^[4-5]. Here we provided evidence, for the first time, on the new distribution of those snails in the Taihu Lake-the third largest freshwater lake in China. Its region is one of the most developed areas of China for agriculture, industry and commerce and playing a critical role in Chinese economy.

1.   Methods and materials

The sampling was carried out between the 27 May and 7 July, 2004 in the Taihu Lake of China (Fig. 1). Invertebrates were hand-collected, preserved in 70% ethanol in the field and returned to the laboratory. All aquatic invertebrates were sorted and identified to the lowest taxonomic level possible under a stereomicroscope.

Figure  1.  Sketch map of the Taihu Lake, China

① Sampling site of P.acuta; ② Sampling site of F.wautieri

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2.   Results and discussion

Two of the snail species we found during our investigation are identified as MIROLLI 1960. So far, no information has been available on those snails in the Taihu Lake. Two specimens of F.wautieri(Fig. 2) were found in the southern part of the Taihu, close to Huzhou city. We found the two snails (1.4 and 2.1 mm) grazing on a stem of a reed (Phragmites communis).F.wautieri is an up to 8 mm long planorbidae, with origin in the Near East^[6]. It is mainly found on stems and leaves of waterplants, but also on stones and other hard substrate in running and lentic waters. It feeds from detritus and periphyton, is tolerant towards salinity, oxygen deficit, drying and high water temperature, and prefers eutrophic waterbodies^[7-9].F.wautieri is known to reproduce through self-fertilization, so that this species is able to set up new populations even in low abundances.F.wautieri might be introduced to the Taihu area via aquatistic materials like waterplants, or navigation, or waterbirds. We suspect that this species has lived in this region for a longer time, but because of its scarcity and small size it was overlooked.

Figure  2.  F.wautieri MIROLLI 1960 found in the southern water of the Taihu Lake, China

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Twenty-eight specimens of P.acuta (Fig. 3) were found in the Wulihu water, a bay in the north of the Taihu. We found them grasping on stones. Many specimens collected in the present study suggest that P.acuta is quite abundant in this region of the Taihu and established its own population some time ago. Because it is also spread with waterbirds, navigation and often found in aquariums^[10], we suspect that it will spread to the Taihu area very soon.

Figure  3.  P.acuta DRAPARNAUD 1805 found in Wulihu water of the Taihu Lake, China

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P.acuta is an up to 20 mm long physidae and although almost certainly native to North America, P.acuta has been spread through human agency around the world^[10]. It is a cosmopolitan, and most common in lentic waters, especially in rich, disturbed and artificially eutrophic environments. It is mainly found on waterplants and hard substrates, feeds from detritus and periphyton and is tolerant towards salinity and high water temperatures^{[7-8, 11-13]}.

P.acuta is an R-selected species, in the sense of Dillon^[14].Its rapid maturation, high reproductive rate, and ease of culture have made it the " fruit fly of malacology " producing scores of detailed studies on life history^[15], behavior^[16], competition^[17], and predation^[18-21]. In China, P.acuta is known from the Heilongjiang Province and Inner Mongolia^[22]. It has been introduced to Shenzhen via Guangdong Province and Hong Kong^[23]. It is also known to be a host of the parasites Angiostrongylus cantonensis CHEN 1935 and Echinostoma revolutum FROHLICH, 1802^[23].

The species F.wautieri and P.acuta are cosmopolitans and known in many countries as introduced species^[3]. Therefore they will potentially spread in the Taihu Lake and even eastern part of China, soon. The present study calls for greater awareness of invasive species (including snails) in the Taihu Lake. Corresponding research and ecological risk assessment should be implemented.