Phases of Penetration of New Species in Freshwater Ecosystems
Introduction of exotic species into areas where they do not naturally occur, are important cause of ecological disturbance and loss of biodiversity. The translocation of fish had become a big problem of global extent and in freshwater communities there are numerous examples of negative impacts of new species. Sometimes effect of biological invasion may be considered as ecological stress for the ecosystem. However, for the other side, in many occasions of fish acclimatization had failed (success was only in 17%). Further, some fish communities appear a strong ability to resitinvasions by introduced fishes related to interaction and structural complexity at the community level. Therefore, the success of invaders and effects of introduction are difficult to predict. In this report only one moment will be observed – the sharply increasing of abundance of new species in freshwater ecosystems. This situation was observed in Karelian Syam-Lake after invasion of smelt (Osmerus eperlanus), when at the first time smelt have a burst phase (increasing in abundance) and sharply change trophic vebs, but later the smelt abundance is sharply decreasing under influence of food competition with vendace (C. albula), predators and parasites. After the invasion of vendace in Pasvik-River we observed the changes in the structure of fish community: 1) vendace had become the DOMINANT SPECIES in the pelagic zone, decrease in the contribution of sparkly whitefish (C. lavaretus); 2) deplacement of plankton-feeding densely-rakered whitefish; 3) big changes in the food nets of all community. Many carnivorous fishes (trout – Salmo trutta, pike – Esox lucius, perch – Perca fluviatilis and burbot – Lota lota) begin to eat vendace. Different phases of introduction new species in ecosystem may be recognized as foolowing: 1) LATENT or GIDE period – slowly increasing of invader abundance, distribution of new biotops, use the food supply, to prevent from predators, finding of spawning place etc. This period may be plolongated: for example; for Caspian kilka Clupeonella cultriventris from Volga reservoirs – 5–10 years, for vendace in Pasvik-River – 10 years, for whitefish in Sevan Lake – 40 years. 2) BURST PHASE (or in the past – effect of acclimatization) – rapid increasing in population abundance and biomass. It last 3–5 years and depend the duration of life-spine of invader. 3) FALL PHASE – sharply decreasing of abundance. The time of this phase is equal the burst pase – 3–5 years. 4) PHASE of STABILIZATION or phase of acception in the ecosystem may be long on ten´s years (as rule the food competition, predator and parasite put the new species in the “place”). The appearance the new species may be considered as invasion or aggression, which may raze ecosystem to the ground. We know the destructive results of inculation of comb-jelly Mnemiopsis leidyi in the waters of Caspian and Black seas, which destroyed all ecosystems from plankton up to fish. But from another side, the acclimatization of Kamchatka crab Paralithodes camtschaticus in the Barentz Sea and self-settling of Caspian kilka Clupeonella cultriventris in the Volga reservoirs have not only negative results, but have and positive ones. It is necessary to emphasize, that sometimes the ecosystems may control the invader and may remove the new species. At present we can't see dangerous from comb-jelly M. leidyi; the communities of the Black and Caspian seas have the organisms, which may control the abundance of comb-jelly. After the introduction new species the ecosystem pass different phases, and if we have a process of naturalization during the last phase of stabilization we observed the fluctuation of abundance new species with waves during 5–7 years (for vendace); the undulating of abundance depent of life-spine new species and the undulation of food supply.