The dispersal of the freshwater hydrozoan Craspedacusta sowerbyi Lankester, 1880, from its presumed original distribution in China to many parts of the temperate and subtropical world has been described in a number of papers (e.g. Reisinger 1972, Rayner 1988, Dumont 1994, McAlpine et al. 2002). Two main hypotheses, alone or in combination, have been proposed to explain its success: first, the dispersal may be supported by human activities; and second, higher temperatures due to climate change may open new areas for invasions. No hard data exist to support any of these hypotheses, but it seems relevant that dispersing vectors are involved in the fast intercontinental range expansion, and low temperatures have, in fact, been shown to be harmful for some of the life stages (see review by Acker Muscat 1976).
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