Reproductive biology of Dikerogammarus haemobaphes: an invasive gammarid (Crustacea: Amphipoda) colonizing running waters in Central Europe

Dikerogammarus haemobaphes is a Ponto-Caspian gammarid that has invaded vast areas in Central and Western Europe. Our paper is a first presentation of its life history features in an invaded region. The study was conducted in the Vistula River in Poland from autumn 2003 to autumn 2005 in two sites differing in hydrological conditions with one being water reservoir. The results showed that the reproductive period lasted 8 months from April till October in both sites. Three generations per 1 year were observed: autumn (overwintering), spring and summer. Ten cohorts per year were distinguished. The individuals from the reservoir were much bigger than those from the other site. The fecundity of those specimens was also higher and they laid 52 eggs per clutch in average in comparison with 37 eggs in the river itself. The strong relationship between the number of embryos (in developmental stage 2) per clutch and the length of females was noticed. The overall mean egg size of stage 2 of D. haemobaphes was 0.430 ± 0.029 mm which is smaller than noted for native species such as Gammarus fossarum. A potentially high reproductive capacity, comparatively small eggs, short time of eggs’ development, fast reaching sexual maturation, short life span, tolerance to a wide range of environmental conditions, all promote the invasion of this Ponto-Caspian gammarid in freshwater ecosystems of the temperate climate zone.