Biogeography

Determining geographical distributions of bryozoan species and higher taxa today – and more especially in the geological past – is hampered by inadequacies in taxonomy and our poor knowledge of faunas from some regions of the globe. For example, a recent study (Dick and Grischenko 2017) of the bryozoan fauna close to a marine station in Okinawa found that 86% of the 52 species detected were either new species or previously unrecorded in Japan. Remarkably, there has been no modern synthesis of the global biogeography of living marine bryozoans. The biogeography of present‐day bryozoans undoubtedly bears the strong imprint of human activities, with many species having achieved pan‐oceanic distributions through transportation on ships’ hulls or in their ballast tanks. Less easy to explain are palaeogeographical distributions that imply transoceanic migrations of bryozoans that are known, or are assumed, to have had short‐ lived larvae. Rafting may have been a more important vector of dispersal than is generally acknowledged, with rafting events that are rare in ecological time being relatively common in the vastness of geological time. Bryozoans at the present day seem not to exhibit the strong latitudinal gradient of diversity increase towards the equator that characterizes many other marine and terrestrial phyla.