Determinants Of the Distribution Of Apple Snails In Hong Kong Two Decades After Their Initial Invasion

Abstract

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.

Secondary production and diet of an invasive snail in freshwater wetlands: implications for resource utilization and competition

“…The high secondary production of P. canaliculata in Hong Kong indicates that it has the potential to monopolize resources, which might account for its successful establishment over the last two decades in almost all potentially suitable habitats in the territory (Kwong et al 2008). Macrophytes were an important dietary component of apple snails in all 4 habitats investigated.…”

“…In Hong Kong, it has spread to occupy most low-lying (\100 m asl) wetlands, including streams, flooded agricultural land, marshes and fish ponds (Yipp et al 1991;Dudgeon and Corlett 2004), although it does not thrive in habitats that have waters with low alkalinity or phosphate and is not found at sites where Ca 2? concentrations are \9 mg l -1 , such as some low order streams (Kwong et al 2008). Pomacea spp.…”

Complex interactions among fish, snails and macrophytes: implications for biological control of an invasive snail

“…Their specific identities have recently been clarified, resolving considerable confusion (Hayes et al 2008). They were first introduced into Asia as a delicacy and a source of protein in the early 1980s, but soon escaped aquaculture and established wild populations in various countries (Chang 1985;Mochida 1991;Halwart 1994;Naylor 1996;Cowie 2002;Teo 2004;Kwong et al 2008). Because of their high fecundity, quick growth and voracious appetite for vegetation, these species have become important pests in agricultural and non-agricultural wetlands, causing tremendous damage to rice production, as well as to wetland floral diversity and ecosystem functioning (Cowie 2002;Carlsson et al 2004a;Carlsson and Lacoursière 2005;Carlsson and Brönmark 2006;Joshi and Sebastian 2006).…”

A lentic dweller in lotic habitats: the behavior of the invasive South American apple snail Pomacea canaliculata in flowing water

“…This may be related to the upstream decrease in water alkalinity and abundance of macrophytes in the streams running from Ventania mountains (Limbozzi and Martín 2003;Martín 2003) or to the increase in hydraulic stress due to the higher slopes of the headwaters (Martín 2003). However, P. canaliculata is able to colonize waterbodies with lower alkalinities (42 mg CaCO 3 L -1 , Kwong et al 2008) than those recorded in the headwaters (111 mg CaCO 3 L -1 , Martín 2003) and is an herbivore-omnivore with a wide trophic spectrum (Estebenet 1995). The snails are probably able to surmount reaches of moderate water velocity, especially crawling near the water edge where current is slower, but unable to trespass riffles or small waterfalls whose frequency increases upstream.…”

“…Therefore, spread of P. canaliculata would depend on two different mechanisms of dispersal: crawling exclusively and drifting, accidentally or not. The results of the detachment trials showed that differentiated snails usually detach at lower velocities, a characteristic that could be enhanced by reproductive behavior, since Kwong et al (2008) observed that snails are more prone to drift during mating.…”