1. Biological invasions have become a serious threat to ecosystems worldwide. Various factors can contribute to the success of biological invasion. We examined how different macrophyte food affected feeding and life-history traits of the invasive herbivorous snail Pomacea canaliculata, and whether differences in snail life-history traits could explain its successful infestation of agricultural and non-agricultural wetlands in Asia. 2. We tested five cultivated and five wild semi-aquatic macrophytes. Snail daily feeding rate varied substantially with plant species, ranging from 1.3% to 22% of its body mass. Snails fed with four (Amaranthus gangeticus, Apium graveolens dulce, Ipomoea aquatica and Nasturtium officinale) of the five cultivated macrophyte species exhibited high survivorship, fast growth and high fecundity. Snails fed with Colocasia esculenta, however, grew poorly, did not reproduce and eventually died. 3. Of the five wild species (Eichhornia crassipes, Ludwigia adscendens, Murdannia nudiflora, Myriophyllum aquaticum and Polygonum hydropiper), M. nudiflora supported a high snail survival, but snails had slower growth and lower fecundity than those reared on the four palatable cultivated species. Snails fed with L. adscendens grew substantially slower than those fed with M. nudiflora, and produced only a small clutch of eggs. Snails fed with E. crassipes, M. aquaticum and P. hydropiper had very low survivorship, grew very little and did not reproduce. 4. We determined six plant properties and their correlation with the feeding, growth and reproduction of the apple snails. Cultivated macrophytes in general had a higher nutritional value and lower physical and chemical defences. Phenolic content was negatively correlated with snail feeding rate, while plant nitrogen and phosphorus contents were positively correlated with snail egg production and growth, respectively. 5. These results indicate that, due to their higher nutritional value and lower chemical and physical defences, cultivated macrophytes are in general desirable for the apple snail which may partly explain its successful invasion into wet agricultural areas in Asia. This snail may also selectively graze poorly defended wild macrophytes in non-agricultural wetlands, leading to changes in floral diversity and wetland functioning. Management of this and other apple snails with similar life-history traits should thus focus on the prevention of their further spread.

Invasive species can monopolize resources and thus dominate ecosystem production. In this study we estimated secondary production and diet of four populations of Pomacea canaliculata, a freshwater invasive snail, in wetlands (abandoned paddy, oxbow pond, drainage channel, and river meander) in monsoonal Hong Kong (lat. 22°N). Apple snail secondary production (ash-free dry mass [AFDM]) ranged from 165.9 to 233.3 g m -2 year -1 , and varied between seasons. Production was lower during the cool dry northeast monsoon, when water temperatures might have limited growth, but fast growth and recruitment of multiple cohorts were possible throughout much (7-10 months) of the year and especially during the warm, wet southwest monsoon. The diet, as revealed by stomach-content analysis, consisted mainly of detritus and macrophytes, and was broadly consistent among habitats despite considerable variation in the composition and cover of aquatic plants. Apple snail annual production was[10 times greater than production estimates for other benthic macroinvertebrates in Hong Kong (range 0.004-15 g AFDM m -2 year -1 , n = 29). Furthermore, annual production estimates for three apple snail populations (i.e.[230 g AFDM m -2 year -1 ) were greater than published estimates for any other freshwater snails (range 0.002-194 g AFDM m -2 year -1 , n = 33), regardless of climatic regime or habitat type. High production by P. canaliculata in Hong Kong was attributable to the topical climate (annual mean *24°C), permitting rapid growth and repeated reproduction, together with dietary flexibility including an ability to consume a range of macrophytes. If invasive P. canaliculata can monopolize food resources, its high productivity indicates potential for competition with other macroinvertebrate primary consumers. Manipulative experiments will be needed to quantify these impacts on biodiversity and ecosystem function in wetlands, combined with management strategies to prevent further range extension by P. canaliculata.

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This study examined the relative importance of environmental factors and geographic isolation on the distribution of apple snails in Hong Kong two decades after their invasion from South America. A survey of 61 sites was conducted to collect apple snails and measure 18 environmental parameters known to influence mollusk distribution. Identification of specimens collected in our study was aided by analysis of DNA sequences, and all apple snails collected in Hong Kong were identified as Pomacea canaliculata. Since its initial introduction in the early 1980s, the distribution of this invasive snail has only expanded slightly. Principal component analysis showed that the environmental characteristics of the study sites varied with habitat. Streams were quite homogenous in chemical characteristics and contained little dissolved minerals, whereas ponds, abandoned wet farmlands and drainage channels all showed great variations in nutrient loading. Discriminant function analysis (DFA) revealed that the inhabited sites typically had high levels of phosphate and alkalinity, but the snail was also occasionally found in streams where dissolved ion concentrations and nutrient levels were low. Most of the inhabitable wetlands in New Territories have already been occupied by P canaliculata. Because of its unsuitable hydrology, Hong Kong Island remains uninhabited by this species. Lantau Island has habitable sites for this species, and thus is susceptible for invasion in the future.

The golden apple snail (Pomacea canaliculata), a native of freshwater wetlands of South America, has invaded many Asian countries and grazed heavily in agricultural and wild areas. Common carp (Cyprinus carpio) has been proposed as a biological control agent against this snail, but little is known about its impact on non-target aquatic plants and animals. In a 8-week enclosure experiment, we quantified the impact of common carp on three species of aquatic macrophytes and nine species of snails, including the apple snail, in a shallow pond. The results showed that the apple snail or carp alone significantly reduced the plant biomass, although the apple snail had a stronger overall herbivorous effect than the carp. The carp completely removed juvenile apple snails, but had only a weak predatory effect on larger apple snails and no effect on the adults' oviposition frequency. Furthermore, the carp significantly reduced the populations of most species of other snails that occurred naturally in the pond. Our results thus indicate that common carp can be an effective biological control agent against the invasive apple snail, but caution should be taken about its potential to reduce wetland floral and faunal diversity.