Bythotrephes longimanus in the Commonwealth of Independent States:: variability, distribution and ecology

Bythotrephes is presently extending its distribution to basins throughout Europe and North America. We used long term data (1880-1997) on Bythotrephes longimanus in Eurasian waterbodies to characterize its ecology and tolerance re different ecological factors. Depending on season and environmental conditions of the waterbody, Eurasian B. longimanus:rs may undergo cyclomorphosis and can exist as two distinct forms (B. longimanus or B. cederstroemi). Regional forms of the species (B. l. var. balticus, B. l. var. transcaucasicus, and B. l. var. arcticus) have also been described. Occurrence and density of Bythotrephes populations varies across geographical scales, and are apparently affected primarily by water temperature and salinity. Bythotrephes is limited to regions where water temperature ranges between 4 and 30 degrees C, although the species prefers waters between 10 and 24 degrees C. Bythotrephes tolerates salinity values between 0.04 and 8.0 parts per thousand, though it prefers water between 0.04 and 0.4 parts per thousand. These factors strongly restrict Bythotrephes' distribution in warmer and more saline waters of the Commonwealth of Independent States (CIS), particularly in southern Russia and Kazakhstan. Local abundance and distribution of Bythotrephes is affected by abiotic factors, including basin morphometry and Bushing rate, temperature, oxygen concentration and pH, as well as by lake trophic status and fish predation. Planktivorous fish may restrict habitat use by Bythotrephes to regions of basins where overlap between these groups is minimized. Rivers, canals, and ephemeral waterbodies serve as important modes of Bythotrephes' dispersal throughout the CIS and western Europe. Morphological adaptations (e.g. a long caudal process, cyclic parthenogenesis, and production of resting eggs) permit Byhotrephes to tolerate seasonally inhospitable conditions, assist in its dispersal and range extension, and minimize fish predation.