Mead, A., Carlton, J. T., Griffiths, C. L. & Rius, M., 2011, Introduced and cryptogenic marine and estuarine species of South Africa, Journal of Natural History 45 (39 - 40), pp. 2463-2524: 2472

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http://doi.org/ 10.1080/00222933.2011.595836

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As with other challenging groups, we can only make a first approximation of the numbers of introduced hydroids, especially as these invasions may have commenced in the 1600s. We select, as examples only, 11 species of hydroids as introduced and three species as cryptogenic. There are dozens, if not scores, of species of hydroids that could be considered for candidacy as introduced or cryptogenic in the South African fauna. For example, of the eight hydroid taxa identified to species found by Henschel et al. (1990) on fouling panels in Simon’s Bay (False Bay), we consider two species ( Obelia dichotoma   and Tubularia warreni   , the latter now known as Pinauay ralphi   ). The remaining species, Campanularia integra   , Sertularella arbuscula   , Plumularia setacea   , Plumularia lagenifera   , Nemertesia cymodocea   and Amphisbetia operculata   , are but six examples (all of which are found elsewhere in the world) of a very large guild of species that bear careful global biogeographic, systematic and genetic study. The 11 introduced species treated here originate either from the North Atlantic, Europe, Eurasia (Ponto-Caspian) or are of unknown provenance. As a consequence, the Pacific taxa (for example, those from Japan or the western Americas) are missing from our assessment. Rather than Pacific hydroids not being represented as introductions in the South African biota, it is probable that species from these regions are buried in the very large “cosmopolitan” (and so cryptogenic) hydrozoan element present in South Africa. For all the examples presented, we consider ship fouling and ballast water the most probable vectors.