Epifaunal associates of Fucus serratus at Dale, south‐west Wales

The macrofauna associated with Fucus serratus at Dale in south‐west Wales contained 30 taxa of which five were common: these comprised four encrusting bryozoans and a hydroid. The bryozoans Flustrellidra hispida and Electra pilosa showed significant variations in abundance according to the size and structure of plants colonised. Electra was most abundant on plants where other bryozoans were least numerous. Colony growth in Electra was proportional to the amount of space provided by individual plant segments whilst growth in competitively superior species appeared to be independent of the size of the plant segments colonised. Dynamena pumila was larger and more abundant on larger segment faces where competition was presumably weaker. Each species showed a specific pattern of zonation along the fronds. The dominant species were generally more abundant on the concave surfaces of the plants. There was some evidence for the tendency for certain taxa to co‐occur but the degree of association between species was weak and probably of limited biological significance. Species diversity varied with plant structure. More species occurred on concave surfaces at all plant levels but the overall pattern of diversity on the two segment faces was similar; diversity was greatest in the shrubbier mid‐frond regions. Differential distribution of the dominant encrusting taxa within this Fucus community results in a considerable degree of niche segregation and ecological isolation.