Spatial distribution of Balanus amphitrite and Elminius adelaidae on mangrove pneumatophores

The spatial distribution of barnacles on pneumatophores in mangrove forests near Port Adelaide in South Australia was examined over a period of 18 mo in 1975–1976. Two species of barnacles, Balanus amphitrite Darwin and Elminius adelaidae Bayliss, occur in these mangroves and both were found to occur in aggregations on pneumatophores. Field experiments, using modified pneumatophores implanted as patches in the mangroves, were used to examine the settling behaviour of the cyprids in the period between November 1985 and March 1986. The results of these experiments indicate that the settling behaviour of the cyprids was a major factor in forming and maintaining these aggregations. Cyprids of both species preferred to settle on pneumatophores with adult conspecifics. Pneumatophores with adults of the other species did not attract settlers. Juvenile E. adelaidae also failed to attract settlers. Neither species, however, preferred to settle in contact with the shell of the adult conspecific nor did they avoid the shell of the adult of the other species.