Mobile epifauna on subtidal brown seaweeds in northeastern New Zealand

This paper examines the distribution and abundance of mobile epifauna > 1 mm inhabiting 10 species of subtidal brown seaweeds (Phaeophyceae) in northeastern New Zealand. Cammarid amphipods and isopods were the most abundant animals captured, while a diverse group of gastropods was also present at lower densities F~nely structured seaweeds such as Carpophyllum plumosum var. capillifolium and Cystophora retroflexa tended to support far more animals (up to 2000 ind. per 100 g algal wet wt) than did coarsely structured seaweeds. Comparison of epifaunas among C. plurnosum growth forms of varying thallus width indicated that this pattern was due to the morphology of the plants rather than differences in their internal composition. There was a trend for isopods with tubular body shapes to live on algal species with narrow fronds, and for dorso-ventrally flattened isopods to live on algae with wide fronds. Most of the seaweed species held epifaunal assemblages that were distinct from one another in multivariate space, but the individual epifaunal taxa were generally not strongly host-plant specific, w ~t h most occurring on more than 1 algal species. It is suggested that most of the epifauna have a weak relationship with their host plant. Epifaunal dens~ties on Ecklonia r a d ~a t a peaked at 6 m depth, and declined with increasing depth.