First record of mass occurrence of the tubeworm Ficopomatus enigmaticus (Fauvel, 1923) (Serpulidae: Polychaeta) in coastal waters of the Baltic Sea

The first mass occurrence of the alien, tube building polychaete Ficopomatus enigmaticus (Fauvel, 1923) was found in the Baltic Sea in 2020. Detailed surveys of private marinas, yacht clubs and boats as well as visual inspections, scratch sampling and a camera assisted remotely operated vehicle revealed its occurrence along a 12 km stretch of the lower saline section (7.12-11.67 PSU) of the Warnow River Estuary, Germany in the western Baltic Sea. The species was found mostly in sheltered areas in 1.0-4.5 m water depth, but it was not found in the higher saline areas (14.10- 15.31 PSU) of the estuary or along the coast. Colony densities up to 28,800 ind. m(-2) were detected. The occurrence of the invasive F. enigmaticus has the potential to alter the ecosystem significantly, suggesting that the colony be monitored closely for signs of expansion, establishment and possible alterations to these ecosystems.