One of them is a copepod, Chelicorophium curvispinum, originally from the Black Sea.
Both species reached the Rhine through the Rhine-Danube canal.
Both species may become pests.
However, predators of these species, goby fish, have also found their way from the Danube to the Rhine.
Tubenose goby nest in beer bottle: here.
Tubenose goby nest in shell: here.
This is a video about an invasive goby in the Netherlands.