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 t o habitat selection. The influence of natural epilithic microbial foul ing organisms on the settlement of Semibalanus balanoides cyprids (Cru stacea: Cirripedia) was examined using laboratory and field based inve stigations. In choice chambers, cues from microbial films were importa nt; cyprids preferred surfaces with a mature microbial film to either unfilmed surfaces or those with a developing film. Cyprids also discri minated between filmed rocks from different tidal heights, preferentia lly selecting those from the mid-shore which is their usual zone. Film ed surfaces which had previously been colonised by barnacles were sele cted in preference to unfilmed surfaces, but the presence of an adult barnacle did not enhance settlement on either filmed or unfilmed surfa ces. However, laboratory experiments were not consistent with settleme nt in the field which was predominantly influenced by the proximity of conspecifics and by traces of previous barnacle colonisation. These f actors increased settlement, and seemed to over-rule cues from microbi ota within the film. Difficulties in the application of laboratory bas ed studies to settlement in the natural environment are discussed.