LABORATORY STUDIES OF GREGARIOUS SETTLEMENT IN BALANUS-BALANOIDES AND ELMINIUS-MODESTUS IN RELATION TO COMPETITION BETWEEN THESE SPECIES

Mixed cyprids of Elminius modestus and Balanus balanoides were offered pits suitable for settlement containing either (1) no previous settlement, (2) settled spat of their own species, (3) spat of the other species, or (4) spat of both species. Settlement was always reduced by the presence of previous colonizers (territoriality) but biased towards pits containing spat of their own species (gregariousness). The conclusion that barnacle cyprids are gregarious, even at very close range, is contrary to the previous findings of Knight-Jones & Moyse, who believed that interspecific competition was enhanced by a tendency for cyprids to settle preferentially close to other species. Our experiments indicate that greater intraspecific competition and a separation of species will result from the behaviour of barnacles at settlement. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.