Comparative Ecology of the Alien Freshwater Snail Potamopyrgus antipodarum and the Indigenous Snail Semisulcospira spp.

Abstract

Density in relation to habitat of the alien freshwater snail Potamopyrgus antipodarum and the indigenous Semisulcospira spp. were investigated for a year in a channel in Moriyama City, Shiga Prefecture, central Japan. Water depth, velocity, water temperature, DO, pH, EC, Ca^<2+>, COD, NH^<4+>, NO^<3+> and substratum were measured and analyzed as environmental factors. As a result of variable selection following Hayashi's Quantification Theory Type I, velocity and substratum were selected most frequently by both P. antipodarum and Semisulcospira spp. The density of P. antipodarum was low throughout the year on a pebble substratum, whereas other combinations of environmental factors and species varied between sampling seasons. Laboratory experiments showed that adult Semisulcospira had no preference for any kind of substratum, whereas juveniles preferred a tile bottom with algal cover to a sandy bottom without cover. Adult P. antipodarum preferred a tile bottom with pebble cover or a sandy bottom with algal cover whereas the juveniles preferred substrates with any kind of cover. Adults and juveniles of both species preferred a slow current of less than 10 cm/s. The large gap between field survey and laboratory experimental results suggests that the tolerance ranges of substratum and velocity are much broader than the preferred ranges of both snail taxa. Juvenile P. antipodarum was less tolerant of water flow, suggesting that populations cannot establish themselves in turbulent flow on a coarse substrate.