Tidal settlement of the intertidal barnacles Chthamalus spp. in SW Portugal: interaction between diel and semi-lunar cycles

摘要

Patterns and processes of tidal settlement (within 1 tidal cycle) of Chthamalus spp. in SW Portugal were investigated during the summer of 2003. Settlement patterns in relation to different periods of the day (night and day) and semi-lunar tidal cycles (spring and neap tides) were assessed using artificial plates deployed in intertidal habitats dominated by C. montagui. Settlement of Chthamalus spp. varied at all temporal and spatial scales considered in this study. A strong interaction between diel and semi-lunar tidal cycles was detected. Settlement was higher during diurnal spring tides (afternoon) than during diurnal and nocturnal neap tides (morning and early night) and was lowest during nocturnal spring tides (late night). In order to investigate putative physical mechanisms of shoreward transport to explain our observations, the tidal variability of several physical variables (wind stress, seawater temperature and temperature stratification) was individually investigated and correlated with settlement. Onshore wind stress was positively correlated with settlement, and exhibited the same night/day and tfdal pattern. Onshore wind forcing could be acting as a mechanism promoting intensive larval delivery to the shore in the afternoon (sea breeze) and offshore retention late at night, leading to the high frequency variability patterns observed in barnacle settlement.