Diurnal behavioural patterns and spread of the Ponto-Caspian invader Hemimysis anomala G. O. Sars, 1907 (Crustacea, Mysidacea) in the Elbe River, Czech Republic

The Ponto-Caspian invader Hemimysis anomala was studied in the river Elbe, Czech Republic. The study confirmed further spread of the species: the presence of juveniles and gravid females indicated that H. anomala is established within the Elbe River. Bottom, mid-water and surface drift samples were collected during 24-h cycles from July to September 2007. A tendency to remain hidden was the main behavioural strategy of H. anomala in the riverine environment. The mysid was found mainly in the bottom and mid-water layers, and observed density and mean length of drifting individuals increased with decreasing light levels, being highest at night. Similarly, density and mean length of drifting individuals increased with increasing turbidity. The effect of turbidity on density was particularly apparent during the night samples, suggesting further advantage to night-drifting individuals. ((c) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)