Ponto-Caspian amphipods in Croatian large rivers

Abstract

This study examines distribution of non-indigenous amphipods in Croatian large rivers and hypothesizes distributional changes of alien and native amphipods in these rivers on the basis of historical records. Samples were collected at 42 sites in the Sava, Drava, Kupa and Danube Rivers during the period from 2004 to 2008. Occurrence of five Ponto-Caspian amphipod species was recorded: Chelicorophium curvispinum, Dikerogammarus bispinosus, D. haemobaphes, D. villosus and Obesogammarus obesus. C. curvispinum was the most widespread species, recorded in all four examined rivers, at 20 sites in total. This species now inhabits the whole Croatian part of the Danube River and it has invaded Sava and Drava Rivers, about 500 and 210 km upstream from the mouth, respectively. D. villosus was the dominant gammarid species at all sites in the Danube. The species was also found in the section of the Drava River up to 175 km upstream from the river mouth, but it was not recorded in the Sava River. D. haemobaphes exhibited the same distribution in the Sava River as C. curvispinum, while in the Drava River it was found only at two sites (175 and 195 km from river mouth). D. bispinosus and O. obesus were recorded only in the Danube. Based on the comparison of historical records with present distribution of non-indigenous amphipods in the middle course of Danube, Sava and Drava Rivers, we conclude that C. curvispinum and D. haemobaphes were the first Ponto-Caspian invaders in these rivers, followed by O. obesus only in Danube and D. villosus in Danube and Drava. The latter species replaced D. haemobaphes in the middle part of Danube and in lower course of Drava, while it did not colonize the Sava River.