First occurrence of the non-native bryozoan Schizoporella japonica Ortmann (1890) in Western Europe

Schizoporella japonica Ortmann was described from Japan but was subsequently introduced on Pacific oysters to the Pacific
coast of North America, where it is now well established. In this paper we record it for the first time in European
waters. The initial discovery was in a marina at Holyhead, North Wales, in July 2010 but S. japonica has since been observed
abundantly in the Orkney Islands (from May 2011) and, subsequently, at other localities in northern Scotland. Introduction
seems most likely to have been on an ocean-going vessel. The British material is here fully described and
illustrated with SEMs and colour photographs; some unusual characters are discussed. Unlike other recently introduced
bryozoans, S. japonica is a cold-water species and its breeding season in Britain extends through the winter. Extensive
confusion between this and other species of Schizoporella on the west coast of Canada and the USA led us to make thorough
morphometric comparisons between the species concerned (Schizoporella unicornis (Johnston in Wood),
Schizoporella errata (Waters) and Schizoporella pseudoerrata Soule, Soule and Chaney). Zooid size in cheilostomate
bryozoans is variable and often an unreliable character for species separation but shape (and therefore ratios between variables,
which are independent of size) are often valuable: S. japonica zooids have a much greater length:width ratio than
the other species. Density of frontal pseudopores provides a useful discriminatory character. Schizoporella unicornis, repeatedly
reported in error from the Pacific coast of North America, does not occur there; it is a European species. Full
comparisons are made between S. japonica and S. unicornis for European identification and between S. japonica, S. errata
and S. pseudoerrata (which are also illustrated) for North American localities.