Larval supply, settlement and survival of barnacles in a temperate mangrove forest

Cyprids of the barnacles Elminius covertus and Hexaminius popeiana were sampled in the water column at differing distances from the seaward edge within a mangrove forest and at different tidal elevations at the seaward edge of a mangrove forest in Sydney, Australia. At differing distances from the seaward edge of the forest, the density of settlers of E. covertus and H. popeiana was correlated with the density and availability of cyprids in the water column. The density of recruits was correlated with the density of settlers and the density of adults with the density of recruits. Cyprids of each species were most abundant in the water column during high tides that occurred during the night. Since most settlement of E. covertus occurs in winter, when nighttime tides are of greater amplitude than at other times of the year, this species has more frequent access to the landward parts of the forest than H. popeiana, which mainly settles in spring and summer. At different tidal elevations at the seaward edge of the mangrove forest, the density of settlers, recruits and adults of E. covertus was correlated with the density and availability of cyprids. In contrast, the density of settlers of H. popeiana among tidal levels was not in concordance with density or availability of cyprids. This is the first example of detailed sampling of cyprids and their survival in a mangrove habitat with calm wave action and a less harsh physical environment than found on rocky shores. In mangrove habitats, the density and availability of cyprids at differing distances from the seaward edge and in the vertical range for 1 species (E. covertus) constituted a good predictor of patterns of settlement.