Moving to the Southern Hemisphere: life-cycle and substratum preferences of the adventive bryozoan Bugulina flabellata (Bryozoa: Cheilostomata) in southern New Zealand

Abstract

Invasive species are a growing problem worldwide. The effects of these invasive species are wide-ranging and include negative impacts both on ecosystem services – such as air quality, available recreational space, reduced food species, and spread of disease – and the economy alike. Many vectors for the introduction of invasive species are of anthropogenic origin – shipping, for example – and post-establishment invasive species can go on to cause significant issues in their new environments. Bryozoans are colonial animals with a number of growth forms, some of which – encrusting and erect, flexible forms, for example – are well-suited for marine fouling of submerged surfaces such as ship hulls, docks, pontoons, and buoys. Bugulina flabellata is one such bryozoan species that has become established here in New Zealand. Primarily known as a marine fouling species outside its native range, it is found in almost all of New Zealand’s ports and harbours. Novel habitats provided by artificial hard substratum in the way of piers, pilings, sea walls, and other such structures are suspected to be preferentially settled by invasive species as is evidenced by a growing body of literature on the subject. This study sought to elucidate potential differences in the life history of Bugulina flabellata between its northern hemisphere native range and a southern hemisphere transplant locale – Portobello, Otago Harbour, southeastern New Zealand – as well as to determine whether it exhibited a preference in choice of substratum. Bugulina flabellata was found to differ in its life history in New Zealand in terms of its overwintering strategy, the length of time embryos were found to be present, and its attachment to bare substratum. No significant difference was found in the number of colonies settled on three types of 25 cm2 settling plates – powder-coated sheet steel, slate, and PVC. The differences in life history and the lack of significant preference exhibited by Bugulina flabellata in New Zealand are suggestive of an ecotypic adaptation to its Southern Hemisphere environment. As such, it is likely that the species, given enough elapsed time, will continue to spread outside of the limited range – ports and harbours – that it currently inhabits. Current information on life cycles should be viewed as guidelines only and will certainly vary between locations. Some aspects of Bugulina flabellata’s life history will be relevant to other bryozoan species, particularly other cheilostomes.