First record of the parasitic copepod (Mytilicola orientalis Mori, 1935) in blue mussels (Mytilus spp.) of the Baltic Sea.
The parasitic copepod Mytilicola orientalis infesting mussels and oysters was so far only described in saline waters - such as the North Sea. In April 2018, it was recorded for the first time at a low salinity location in the Kiel Bight, Baltic Sea. Two mature females of M. orientalis were found in two separate individuals of Baltic blue mussels (Mytilus spp.). Prevalence of parasites in the whole sample was low (3.6%), and no males or eggs were detected. In a second sample from October 2018, another adult female was found indicating spread over larger areas and longer time periods. The findings of this study further indicated that larvae from introduced M. orientalis adults can hatch under low saline conditions of Kiel Fjord and are able to infest and to develop within tissues of Baltic blue mussels. It therefore may just be a matter of time before the establishment of the full life cycle of M. orientalis in the Baltic Sea.