Random and Aggregative Settlement in Some Sessile Marine Invertebrates

Settlement patterns of 4 sessile invertebrates are statistically analysed.In the field, the colonial ascidians Botryllus schlosseri and Diplosoma listerianum settle randomly on perspex panels.Laboratory experiments with D. listerianum substantiate these results and demonstrate that larvae are not attracted towards already attached juveniles.Two solitary species, the barnacle Elminiusmodestus and the ascidian Molgula complanata settle aggregatively, but the latter less strongly than the former.Species differ in their preference for horizontal or vertical panel orientation.The settlement pattern of each species is consistent and not influenced by panel orientation or by the presence of other specles.