Distribution, abundance and recruitment of Chthamalus (Crustacea: Cirripedia) populations along the central coast of Portugal

The distribution, abundance and recruitment of Chthamalus species were studied for one year at two rocky shores on the central coast of Portugal. Chthamalus montagui is the most abundant intertidal barnacle on the Portuguese mainland. Higher abundance of C. montagui was found on the lower levels of the more sheltered shore, which is closer to the influence of the Tagus estuary. Chthamalus stellatus was also present, in very low densities,, and always confined to the lower level of the barnacle zone. Chthamalus stellatus was more common at the shore farther away from the estuary, in which exposure to wave action is higher. The metamorphs or C. stellatus settled at the studied shores are considered to be immigrants from other populations, where the density of adults is sufficient for cross-fertilization to occur. Chthamalus spp. recruited almost continuously throughout the year, with a peak between July and September and a gap during February and March. Variations in phytoplanktonic assemblages and temperature may be the main factors controlling the reproductive season of Chthamalus spp. Recruitment Was usually stronger on the lower shore levels but extended for a longer period higher on the shore. Seasonal variations of C. montagui abundance were greater on the lower levels of the more exposed shore. This is probably due to faster growth and higher mortality of barnacle Populations occupying the lower shore levels at the more exposed habitats.