You have a Chelicorophium curvispinum (G.O. Sars, 1895) – Caspian mud shrimp
Synonyms: Corophium curvispinum; Corophium devium Wundsch, 1912
Common names: Caspian mud shrimp (UK); Süsswasser-Röhrenkrebs (DE); Kaspische slijkgarnaal (NL); Bełkaczek wschodni (PL); Liejukatka (FI)
The maximum length of this species is 9-10 mm, so correct identification to species level requires microscopic examination. The segments of the urosome are not fused. It has prominent spines on antennae 2 peduncle and on uropods, and also dense hairy setae on antennae and pereopods.
Native area: Ponto-Caspian (den Hartog et al., 1992).
Introduced area: In western Europe this species occurs almost exclusively in freshwater and only rarely has it been found in oligohaline waters, such as in the Netherlands (Wolff, 2005), France (Bachmann et al., 1995) and Germany (Nehring & Leuchs, 1999). The earliest European record is from 1912, when it was described as a new species, Corophium devium (Nehring & Leuchs, 1999). It has apparently been introduced unsuccessfully to the U.K. a couple of times (Moon, 1970), and now occurs there in freshwater. In the Baltic Sea area the first reports date back to the 1920s (Jazdzewski & Konopacka, 2000). It was recorded from the Gulf of Finland coast of Estonia (Narva Bay) in 2005 (Kotta et al., 2006).
Vector: Chelicorophium curvispinum most likely spread via shipping through the rivers and canals of central Europe (den Hartog et al., 1992; Nehring & Leuchs, 1999); Jazdzewski & Konopacka, 2000).
They construct mud tubes on hard substrates (den Hartog et al., 1992). In some places it is associated with benthic seaweeds (Kotta et al., 2006). Densities can be extremely high, >200,000 individuals per m² (den Hartog et al., 1992; van den Brink et al., 1993). They are suspension-feeders, filtering phytoplankton, especially diatoms, but also detritus particles. It tolerates salinities up to 6 ppt, and is nocturnal (Nehring & Leuchs, 1999). It prefers strong currents and is often associated with seaweeds (van den Brink et al., 1993). It is an important food item for several fish species (van den Brink et al., 1993; Nehring & Leuchs, 1999).
Reproduction: There are three generations per year; April-May, June-July and September-October. Up to 34 embryos have been observed in one brood, depending on the size of the female (den Hartog et al., 1992). Spawning begins when the temperature is above 12° C and brooding lasts about 2 weeks (van den Brink et al., 1993). Native corophiid species have only two generations per year and may reproduced all year round (van den Brink et al., 1993).
Its introduction to the river Rhine caused dramatic ecological changes, such as a decrease in zebra mussel abundance. This is partly due to their filtration capacity, partly because their tubes form an unsuitable substrate for other organisms (den Hartog et al., 1992). It is even capable of covering zebra mussels with their tubes (van den Brink et al., 1993; Nehring & Leuchs, 1999).