BIOLOGICAL INVASIONS: THE EUROPEAN SMELT OSMERUS EPERLANUS (L.) AND THE MICROSPORIDIAN GLUGEA HERTWIGI WEISSENBERG, 1911

The paper presents the phenomenology of the smelt Osmerus eperlanus and the microsporidian Glugea hertwigi invasion into a new habitat - Lake Syamozero (Karelia), where neither of the species occurred before. The invasion history falls into 4 phases. The first, latent phase started with a spontaneous invasion of the lake by smelt and lasted until the first fish showed up in catches (1968-1970). The second phase (1971 to 1980) was the invader number outbreak. The smelt became the dominant species in the fish community, while the native plankton-feeder, the vendace Coregonus albula, became an endangered species. The third phase (1980 to 1991) was the population outbreak of the microsporidian Glugea hertwigi, and development of an epizootic. The fourth phase (since 1991 until present) is the decreasing of the number of the invasive species - the smelt and the microsporidian Glugea hertwigi and the recovery of the native vendace population.