The occurrence of two non-indigenous Conopeum (Bryozoa: Cheilostomata) species in the coastal waters of South Korea

Bryozoans are major fouling organisms and include some of the most invasive marine species globally. Hull fouling of transoceanic vessels is a major vector of non-indigenous bryozoans. One genus known to be important in this regard is Conopeum, but its occurrence in the coastal waters of South Korea has yet to be established. We sorted bryozoan samples from the collection of Park et al. (2017) and carried out surveys for marine organisms in 2013 and 2019–2020 in coastal waters of South Korea. We found two non-indigenous bryozoans: Conopeum reticulum (Linnaeus, 1767) and C. seurati (Canu, 1928). These two species and a third in the genus, C. hexagonum Seo, 1996, have distinctive morphologies and distributions along environmental gradients of the sampling sites. Gymnocyst and cryptocyst development and spine presence were used to identify each species morphologically. According to the salinity and turbidity of the sites, the inhabiting species appeared differently. The two nonindigenous species occurred in association with other sessile organisms such as oysters, mussels, and serpulid polychaetes. In particular, C. reticulum was associated with an invasive species of the Mediterranean mussel (Mytilus galloprovincialis Lamarck, 1819) and C. seurati was associated with the serpulid polychaetes Hydroides ezoensis Okuda, 1934 and Ficopomatus enigmaticus (Fauvel, 1923), as well as with the mytilid bivalve Xenostrobus securis (Lamarck, 1819), and the Pacific oyster Crassostrea gigas (Thunberg, 1793). Conopeum seurati and H. ezoensis completely encrusted all surfaces in artificial canal docks seemingly negatively affecting richness of native species.