Can the invasive New Zealand mud snail (Potamopyrgus antipodarum) threaten fisheries of temperate lakes? A case study from Lake Dusia, Lithuania.
Background. To date, numerous studies of the impact of snail Potamopyrgus antipodarum (Gray, 1843) on invaded ecosystems have been conducted. However, the majority of such studies intended to assess changes induced in macroinvertebrate assemblages, while the possible effects of P. antipodarum on higher trophic levels have not hitherto been studied. Of particular interest from the point of view of fisheries management is the elucidation of how this invasive snail can alter the energy flow towards higher trophic levels. When abundant, P. antipodarum consumes a substantial part of the primary production, but it is poorly consumed by native fishes. Consequently, part of its assimilated energy may become locked in lower trophic levels and fail to reach higher levels directly. Therefore, invasion of this snail may decrease fish production. Materials and methods. Several years after establishment of P. antipodarum in a temperate mesotrophic Lake Dusia, we assessed: (1) changes in the biomass of littoral macroinvertebrates (proxy to secondary production), (2) assimilation of P. antipodarum by benthivorous fish (energy flow), and (3) changes in growth and catches of littoral benthivorous fish (fish production). All the analyses were based on a merger of "grey" literature and original data during the pre- and post-invasion periods. Results. There was an evident increase in the biomass of littoral macroinvertebrates, and the assemblage changed from crustacean- to gastropod-dominated due to over-domination of P. antipodarum. However, P. antipodarum did not replace the native prey of fish. Moreover, a marked decrease was recorded in littoral fish growth and catches after the invasion of P. antipodarum. Conclusion. Dense populations of P. antipodarum may reduce the channelling of primary production towards higher trophic levels and, consequently, the invasion may threaten fisheries of temperate mesotrophic lakes.