Bellamya chinensis (mollusc)
In juveniles the last shell whorl displays a distinct cartilaginous ridge (carina) and the shell contains grooves with 20 striae/mm between each groove. Juveniles also have a detailed pattern on their periostracum consisting of 2 apical and 3 body whorl rows of hairs with long hooks on the ends, distinct ridges and many other hairs with short hooks.
Considerable variation between individuals exists, and distinct shell variations have been designated as morphotypes assumed to reflect variations in allometric shell growth in different environmental regimes (AIS, 2005; Prezant et al., 2006; Benson, 2007; Kipp & Benson, 2011; Soes et al., 2011).
It has been found in depths of 0.2-3 m and waters with pH of 6.5-8.4, conductivity of 63–400 μmhos/cm, and concentrations of calcium (5-97 ppm), magnesium (13-31 ppm), oxygen (7-11ppm), and sodium ( 2–49 ppm) (Jokinen 1982; Jokinen 1992 in Kipp & Benson, 2011). It can tolerate conditions in stagnant waters near septic tanks (Perron & Probert, 1973 in Kipp & Benson, 2011). A recent study also suggests that B. chinensis is highly resistant to desiccation, giving potential for overland transport via boats (Havel, 2010).
Competition: Presence of B. chinensis was found to cause substantial declines in the growth and abundance of native Physella gyrina and Lymnaea stagnalis snails in mesocosm experiments, probably through competition for food (Johnson et al., 2009). However such negative impacts on native gastropod assemblages have not yet been confirmed in field studies. Solomon et al. (2010) found no difference in snail assemblage structure associated with B. chinensis presence or abundance at the scale of an entire lake, although some native snail species tended not to occur at sites where B. chinensis was abundant.
Ecosystem change: In a mesocosm experiment B. chinensis grazing was found to reduce algal biomass, algal species composition and increase the N: P ratio in the water column. Such effects may have important ecological consequences (Johnson et al., 2009).
Interaction with other invasive species: In a mesocosm experiment in Wisconsin, the dual effects of predation by an invasive crayfish (Orconectes rusticus) and competition by B. chinensis were found to have more severe impacts on native snail species than either invader alone. Due to its large size and thicker shell B. chinensis was less vulnerable to predation by this crayfish. The combined impact of both invasive species was found to extirpate one native snail species and reduce the abundance of a second by >95%. This may be because O. rusticus reduces native snail abundance via predation but has limited effects on B. chinensis, thus promoting additional food resources for B. chinensis (Johnson et al., 2009).
An experimental study in Washington suggests that B. chinensis may facilitate establishment and exacerbate the establishment success and ecological impacts of an invasive crayfish (Orconectes virilis) by providing an abundant prey resource (i.e. invasional meltdown). This hypothesis requires further research and testing (Olden et al., 2009).
Human health: B. chinensis is also the host for several helminth parasites that affect humans in native Asia. Thus it may serve as a vector for parasites and diseases, including human intestinal fluke (Chung & Jung, 1999; Havel, 2010; NAPIS, 2010). However there is little data to support this (Soes et al., 2011), and there have been no reported cases involving human intestinal fluke transmitted by B. chinensis in the United States (Bury et al., 2007).
Human nuisance: Shells may clog the screens of water intake pipes and thus inhabit the flow of water (AIS, 2005). Additionally, dead and decaying shells can form large windrows on lake shores, which is viewed as a nuisance by residents in some regions (Bury et al., 2007). In the Laurentian Great Lakes, fisherman often made seine hauls containing “2 tons” of snails, which were likely B. chinensis or B. japonica (Wolfert & Hiltunen, 1968).
Other: B. chinensis were found to provide a novel food resource for both native and invasive crayfish in Washington, despite their thick shell and trapdoor defense behaviour. For all snail size classes native Pacifastacus leniusculus was able to consume greater numbers of snails than an invasive crayfish species. Whether this translates into P. leniusculus having a competitive advantage over invasive crayfish in a natural setting is unknown (Olden et al., 2009).
Two subspecies or variations of Bellamya chinensis are recognized: chinensis and malleata (AIS, 2005; IT IS, 2009).
B. chinensis is thought to be spread overland by attachment to macrophytes on boat hulls. Changing human behaviour such as encouraging removal of macrophytes may reduce the spread of this snail, as well as other invasive species of concern (Havel, 2010).
Chemical control: Copper sulfate is approved by the U.S. Environmental Protection Agency as a snailicide commonly used for control of other invasive snail species. It has recently been used for the first time against B. chinensis in Jackson County, Oregon. While 100% eradication has not been achieved, it may be a successful method for controlling populations (Freeman, 2010).
Prezant et al. (2006) found that in the presence of crayfish predators B. chinensis may exhibit predator-induced defensive responses. Females in the presence of crayfish released significantly more juveniles than control females, and juveniles were smaller, more variable in size and had higher organic content of shells. The generally smaller size of juveniles released in the presence of a predator reflects a faster rate of generation and passage through the uterus.
Young are born live and fully formed and growth is allometric (the height of the shell increases more rapidly than the width). The lifespan is four to five years (Jokinen, 1982), and individuals have the potential to overwinter in cold conditions (Rixon et al., 2005).