The conquest (and avoidance?) of the brackish environment by Ponto-Caspian amphipods: A case study of the German Baltic Sea

摘要

Although an invasion of the brackish water biotopes was to be expected with the appearance of several Ponto-Caspian amphipods in German freshwaters two decades ago (and earlier), only recently (two years ago) the conquest of the mesohaline Baltic Sea could be observed. This discrepancy is a fortiori of interest as previous experimental studies showed that species like Dikerogammarus villosus and Obesogammarus crassus were able to tolerate both mesohaline and also polyhaline conditions. Two decades of invasion history in rivers and lakes have led to drastic faunal changes. If similar or analogue shifts will happen in brackish environments and if estuaries like the Stettin lagoon function not only as “a gate to the Baltic Sea” but also as a “catalyser” or acclimatisation area for invasive species remains to be seen. Simultaneously the question came up, why other also potentially brackish water species failed to colonise mesohaline waters although they partially arrived in the investigation area several decades ago (e.g. Chelicorophium curvispinum and Echinogammarus ischnus ).