The influence of epilithic microbial films on the settlement of Semibalanus balanoldes cyprids - a comparison between laboratory and field experiments

Barnacle cypris larvae show considerable exploratory behaviour prior to habitat selection. The influence of natural epilithic microbial fouling organisms on the settlement of Semibalanus balanoides cyprids (Crustacea: Cirripedia) was examined using laboratory and field based investigations. In choice chambers, cues from microbial films were important; cyprids preferred surfaces with a mature microbial film to either unfilmed surfaces or those with a developing film. Cyprids also discriminated between filmed rocks from different tidal heights, preferentially selecting those from the mid-shore which is their usual zone. Filmed surfaces which had previously been colonised by barnacles were selected in preference to unfilmed surfaces, but the presence of an adult barnacle did not enhance settlement on either filmed or unfilmed surfaces. However, laboratory experiments were not consistent with settlement in the field which was predominantly influenced by the proximity of conspecifics and by traces of previous barnacle colonisation. These factors increased settlement, and seemed to over-rule cues from microbiota within the film. Difficulties in the application of laboratory based studies to settlement in the natural environment are discussed.