An investigation into Rock Surface Wetness as a Parameter Contributing to the Distribution of the Intertidal BarnaclesChthamalus stellatus and Chthamalus montagui

Areas which were under the influence of runoff seeping slowly from upshore rockpools were identified at two shores in Co. Cork, Ireland. Surveys of adult and 0+Chthamalus stellatus and C. montagui were carried out in these areas and compared with adjacent dry areas. A second survey on cleared quadrats examined barnacle abundance in wet and in dry areas at 1 and 5 months after the initiation of settlement. Chthamalus stellatus adults and 0+ individuals were significantly more abundant in wet areas than in dry areas, which in the context of previous laboratory findings suggest that desiccation or some other parameter associated with wetness may be an important factor in limiting the vertical distribution of this species. Chthamalus montagui adults and 0+ individuals were significantly more abundant in dry areas than in wet areas. The lower vertical limit of this species may therefore also be set by some wetness parameter. In 1 month and 5 month old stages, the differences in abundance between wet and dry conditions were apparent in both species but were only significant in both age classes of C. montagui at one of the study shores. The results are discussed in the context of vertical and geographical distribution patterns exhibited by adults of each species on European shores.