Prosobranchia antipodarum Gray, 1843 (Mollusca: Gastropoda) Is Invasive Species in Fresh Water Bodies of Kaliningrad Region (Russia)

Gastropod molluscs were collected during summer 2008 on the littral zone of four reservoirs – three artificial lakes (last sand-pits) and river. These lakes (Lake Forelevoje and Golubuje Lakes) are represented a grope situated along the shore of SW Kaliningrad Gulf (the part of Vistula Gulf aquatory) and pertain to oligotrophic type. The sand and sand-gravel substrates are dominate in lakes. In Zelenogradka river molluscs samples were picked along lower reach river.

During investigation period 29 gastropod mollusc species were found in water bodies. Among them 7 (24 %) species belong to Prosobranchia and 22 (76 %) – to Pulmonata. The largest family revealed in fauna is Lymnaeidae which contains 11 species of molluscs. Te majority of these species were searched out in Forelevoe Lake.

Beside the differences between mollusc specific structures, the P. antipodarum was found in either water body as dominant mollusc, which occurs in the high density: 206 ind./m² (Forelevoe Lake), 864 ind./m² (Zelenogradka River), 237 ind./m² and 1023 ind./m² (Golybie Lakes).

These snails were found in some localities in the various littoral habitats: sand, pebble, rocks in lakes along all the inshore aquatory of lakes, in which connection some of habitats such as filamentous alga aggregates covering branches and boulders include P. antipodarum findings in Goluboje Lake. This scpecies abundance occurred in some localities with density reaching 1884 ind./m² during one month. While in Golubye Lakes mollusc biomass is low, no large mollusc species found in these water bodies.

At the same time these molluscs inhabit actually on macrophytes (especially on brandy-bottle and sagittaria) in river, where were disclosed only on one river section. This species is distributed as were estimated restrictedly through the river, but specific diversity is dramatically decreasing on the point of invasion (fig. 3). The occurrence reachs 97 %, the Shannon index shows minimal mean here (H = 0,16).

P. antipodarum is colonizing the groupe of lakes, when dispersing from Vistula gulf. Iit has become a prevalling species during last years in the gulf and inhabits in abundance involved in main zoobenthic communities (Rudinskaja, 2004), but its occurrence was first described by Vanhöffen (Vanhöffen, 1911). Investigated lakes are connected with Vistula guls by the channel, which influences both on salinity of water and P. antipodarum distribution in these water bodies.