soes d m (2 risultati)

In August-September 2003 a thriving population of the originally southern European land snail Xerotricha apicina (Lamarck, 1822) was discovered for the first time in the Netherlands in a coastal dune area near IJmuiden (prov. Noord-Holland). This probably represents the as yet northernmost record in Europe. In 2003 the population, with animals ranging from tiny juveniles to adults, occupied an area of approx. 70 x 70 m with densities up to 500 (sub)adult animals m-2. In April 2005 the species seemed to have expanded its range by some 50 m. All fresh shells collected are distinctly pilose, whereas most descriptions in the literature emphasize that adult shells are usually hairless, in contrast to juveniles. The species' habitat at IJmuiden is similar to that described in the literature. Since the species possesses a bi-annual life cycle, it must have arrived in 2002 at the very latest, probably some years earlier. The population thus survived the relatively cold winter of 2002-2003 with minimum temperatures of -13 [degree]C close to the site. This, and the availability of suitable habitat nearby, suggests that the species may be able to establish itself firmly in the Netherlands. 6 pp., 9 figs, gr. 8.

In this paper we report on oystercatchers feeding on Corbicula fluminea, a recent invader in the river Rhine. Oystercatchers are specialised molluscivores. They could reach these freshwater bivalves during low river level in the summer of 2003 and in the end of March 2004. The shell remains after consumption have a characteristic damage pattern: the valves still adhere by the ligament and only one of the valves has a (small) piece broken off ventrally. Due to lack of access, oystercatchers cannot use this food source on a regular base as they can with mussels and cockles in tidal areas exposed every low tide. Feeding irregularly on Corbicula shows the oystercatcher's flexibility in food choice. 4 pp., 1 fig., gr. 8.