ABSTRACT
Settlement patterns of barnacle cyprids depend initially on the patterns in which planktonic cyprids come into contact with substrata. Horizontal swimming, which is slow in comparison to wind and tide driven water currents, cannot affect such patterns. However, the bathymetric distributions resulting from vertical swimming can determine the eventual depths of spatfalls. Once solid substrata are encountered, exploration by surface crawling takes place. The rejection of unsuitable substrata by cyprids at this stage accounts for the observed predominance of settlement on suitable substrata. Adverse effects of high settlement densities on suitable substrata may be alleviated by spacing-out behaviours such as ‘territoriality’, which reduce intraspecific spatial competition without reducing interspecific competitiveness. With post-metamorphic growth, crowding may be intensified. Adaptations for survival in crowded habitats in various Balanomorpha include changes in growth rate and morphology, reduction in generation time, and the ability to slide laterally over the substratum. Differences in spatial competitive ability have been shown to lead to exclusion of one species by another. It has been suggested that in evolutionary time, such differences have been responsible for present day biogeographical distribution of major taxa.
