ARKHANGELSK, October 30. /TASS/. Artificially heated reservoirs, like, for example, those at thermal power plants, along with the climate warming, promote the movement of thermophilic freshwater mollusks species to the north. Among such mollusks is the river Dreissena polymorpha - an aggressive invasive species, threatening hydraulic structures as the mollusk can form fouling congregations even on submarines, Director of the Biogeography and Genetic Resources Institute at the Academician Laverov Federal Research Center for Integrated Arctic Studies (the Russian Academy of Sciences' Urals Branch) Yulia Bespalaya told TASS.
"Due to the climate warming, freshwater thermophilic mollusks can move closer to the Arctic borders. Not only that however. This process is facilitated by anthropogenic disturbed reservoirs with altered thermal conditions. The heated water dumping transforms natural habitats promoting the movement of invasive species towards the north. Among them is the river dreissena - one of aggressive invaders," she said.
Unlike insects, which often fly into the northern regions though still are unable to form a stable population due to insufficiently high temperatures for reproduction, the situation with mollusks is different. Heated reservoirs become a kind of refugium - those are shelters where alien species can gain a foothold and begin to reproduce.
Most bivalves are thermophilic. For many species, the breeding threshold is in the range between 12 and 15 degrees Celsius, for corbicula - between 6 and 15 - they can overwinter only in constantly heated water. However, some species, including the dreissen, feel quite comfortable and can breed even in the main watercourse.
"Dreissena was brought to the Arkhangelsk Region through the Severodvinsk Canal in the late 19th century - first finds date back to 1897. The mollusk had passed from the Caspian Sea through the Volga River. Since then, it has naturalized, formed a stable population and has been reproducing steadily. However, the density in our waters is much lower than, say, in the southern regions, where it may reach dozens of thousands of individuals per square meter, while our population is much more modest," the scientist explained.
The troublesome mollusk
Anyway, even in small quantities, the mollusk causes troubles, forming fouling congregations on fishing nets, hydraulic structures, ships and even submarines. When these structures additionally are heated by waste water, the fouling may become critical. Various methods are used to combat dreissena: mechanical cleaning, scraping, special paint coatings, and even chlorine treatment, although the latter is extremely harmful to the ecosystem.
"Dreissena is able to withstand salinity of up to 14 ppm, thus it colonizes marine objects, and also submarines, around which the water is not fresh," the expert said.
Scientists supposed the key to the invasive species' expansion may lie in genetics. Some of the local river dreissen individuals are of hybrid forms - they have fragments of genes, possibly, from other species of mollusks Dreissena rostriformis. Probably, it is this hybridization that gives them an advantage, allowing the mollusks to move further northbound and to adapt to harsh conditions.
"Right now, we are extremely interested in finding out the genetic structure of populations that live in warm discharge waters, for example, near nuclear power plants. We want to find out what kind of mutations or hybridizations allow them to survive in low winter temperatures and to reproduce actively," the scientist told TASS in conclusion.
In addition to the obvious climatic changes, such as warming, the thermal pollution of water bodies from industrial enterprises and energy facilities also contributes to the process. Discharges of artificially heated water from enterprises lead to periodic or prolonged increases in water temperature above the natural level. As a result, oxygen solubility decreases, the water's chemical and microbiological composition changes, the aquatic ecosystems' natural functioning gets disrupted. Consequently, the composition of aquatic organisms will change.
Thermosensitive species die, while thermophilic species, on the contrary, would appear to begin developing actively. Dreissena is a thermophilic species, as its native range is in the Ponto-Caspian and Aral basins. It has settled successfully in the Northern Dvina River long before the industrial development there.