Effects of environment and plant characteristics on the distribution of Bryozoa in a Fucus serratus L. Community

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Five species of Bryozoa were commonly found in the epifaunal communities of Fucus serratus L. plants in Strangford Lough, Northern Ireland. Membranipora membranacea (L.) was most abundant on silt-laden plants in quiet slow-flowing waters, a habitat avoided by the other species. Flustrellidra hispida (Fabricius) and to a lesser extent Alcyonidium hirsutum (Fleming) were more abundant in the faster currents, whereas Electra pilosa (L.) was less abundant here. The responses of the species to their physical environment were modified by the density of Fucus present. Excepting Membranipora the species showed different preferences for plant structure (as measured by total length and degree of bushiness). Each species showed a specific pattern of distribution along the plant fronds, but the interspecific differences were less pronounced on the shorter fronds. Weak preferences in respect of side of frond (concave or convex surface) and of distal or non-distal segments were present. For some species there were major changes in niche breadth or niche position between sites of different environments. All species except Membranipora were more abundant on large than on small segments, even after controlling for plant size, and the number of species on a given segment was strongly correlated with segment area. Species diversity was greatest at about mid-frond level.