First record of the encrusting bryozoan Cribrilina (Juxtacribrilina) mutabilis (Ito, Onishi and Dick, 2015) in the Northwest Atlantic Ocean

The cribrimorph bryozoan Cribrilina (Juxtacribrilina) mutabilis (Ito, Onishi and Dick, 2015), originally described from Hokkaido, Japan, is reported for the first time in the Gulf of Maine and the whole of the Northwest Atlantic coast. In September 2018, numerous colonies of C. mutabilis were collected from eelgrass (Zostera marina Linnaeus, 1753) beds near Clapboard and Mackworth Islands, and Hog Island Ledge, all located within inner Casco Bay, Maine. Bryozoan colonies encrusted eelgrass, rockweed (Ascophyllum nodosum (Linnaeus) LeJolis, 1863), and laminarian drift algae. Situated near the discovery location, the city of Portland (Maine, USA) is an active seaport, suggesting introduction through shipping as a likely introduction mechanism. The North Sea is hypothesized to be the most probable area for the source population. Since C. mutabilis appears to have high potential for introduction, it likely occurs on other parts of the Northwest Atlantic coast where it has yet to be identified and recorded.