Effects of settlement density on spatial arrangement in four intertidal barnacles

Balanus amphitrite was studied in an estuary (Halifax River) in central Florida from October to November 1990, while three other barnacle species were studied on the central coast (Monterey Bay) of California from April 1988 to July 1989. Mean nearest-neighbor distances indicated that in the majority of cases the spatial arrangement of settlers was random for three different balanomorph barnacles-B. amphitrite, B. glandula, and Chthamalus dalli. In Pollicipes polymerus, a lepidomorph species, strong aggregation among settlers was almost always observed. In the three balanomorph species there was no apparent relationship between settler density and the degree of aggregation. In P. polymerus there was a significant positive correlation between settler density and the degree of aggregation. Morphological differences between balanomorph and lepidomorph barnacles may influence the evolution of settlement behavior.