Distribution and abundance of co-occurring chthamalid barnacles Chthamalusmontagui and Chthamalus stellatus (Crustacea, Cirripedia) on the southwestcoast of Portugal

Two co-occurring chthamalid barnacle species occur on the rocky shores of c ontinental Portugal: Chthamalus stellatus (Poli) and Chthamalus montagui So uthward. In the present study, patterns of distribution and abundance (dens ity and percentage cover), both vertically (tidal level) and horizontally ( wave action), were studied for each species on headlands (more wave action) and not on headlands (less wave action) and at two spatial scales (shore a nd site) and three tidal levels (low, mid and upper). Chthamalus montagui w as significantly more abundant than C. stellatus in both degrees of wave ac tion and at all tidal levels, Despite this great difference in abundance an d considering each species individually, C. montagui was more abundant at m id tide-level, while C. stellatus was more abundant at the low tide-level, and C. montagui was less abundant on headlands, while C. stellatus was more abundant on headlands. Small-scale variability (between sites, tens of met ers) of abundance of each species was detected, while differences on a larg er scale (between shores, tens of kilometres) were not significant.