Invasion of the Zebra Mussel Dreissena polymorpha (Pallas, 1771) (Dreissenidae) in Lake Ladoga

Abstract—In May 2019, the invasive mollusk Dreissena polymorpha (Pallas, 1771) was found in Volkhov Bay of Lake Ladoga by means of an unmanned underwater vehicle. The age of some mollusks reached five years, indicating the successful introduction of this species. Underwater video filming made it possible to reveal the features of the distribution of the mollusk in the part of the water area investigated. Mollusks were located singly and more often on the lateral surface of large boulders; they were much less common on pebbles and soft ground. The alternation of the areas of coarse material and sand, characteristic of the littoral of Volkhov Bay, preconditioned the heterogeneity of the distribution of the invader. The highest population density of the zebra mussel was observed at the depths exceeding 4.5 m. The development of adult mollusks in the low-mineralized water of Lake Ladoga indicates its possible naturalization and does not exclude the further spread of the species under the conditions of a changing climate in this water body.