Microbiome acquisition during larval settlement of the barnacle Semibalanus balanoides

Barnacles are conspicuous members of rocky intertidal communities and settlement of the final larval stage, the cyprid, is influenced by the presence of biofilms. While modulation of cyprid settlement by biofilms has been studied extensively, the acquisition of a specific microbiome by the settling larva has not. This study investigated settlement in the field of Semibalanus balanoides in two consecutive years when the composition of the benthic bacterial community differed. In both years, settling cyprids adopted a specific sub-set of benthic bacteria that was distinct from the planktonic cyprid and the benthos. This microbiome was consistent, regardless of annual variability in the benthic community structure, and established within hours of settlement. The results imply that a natural process of selection occurs during the critical final transition of S. balanoides to the sessile form. The apparent consistency of this process between years suggests that optimal growth and survival of barnacles could depend upon a complex inter-kingdom relationship, as has been demonstrated in other animal systems.

Absence of gregarious settling Behaviour by female cypris larvae of British parasitic rhizocephalan barnacles

Barnacle cypris larvae, the specialized settlement stage of the life-cycle, are classical examples of larvae showing gregarious settlement. Gregarious settlement is shown when the larva is induced to settle by established individuals of its own or of a closely related species, reflecting the ability of the larva to recognize its own type, usually by chemo-tactile detection of a particular settlement inducing factor (see Crisp (1974) for review). Sessile barnacles such as species of Balanus or Chthamalus are typically hermaphrodite and gregarious settlement is of selective advantage in promoting the possibility of cross-fertilization, in addition to allowing a settling larva to identify a habitat providing all the necessary conditions for barnacle growth and development.

The ultrastructure and histochemistry of the larval cement of Ostrea edulis L.

The larval cement of Ostrea edulis is formed from material secreted by the settling larva from two types of pedal gland (Cranfield, 1973b). Light microscope observations suggested that there were fibrous regions in this cement. The histochemistry and ultrastructure of the cement were therefore examined to establish the nature of this fibrous structure and to determine the part each of the two secretions might play in its formation.