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Abstract

Bacterial films on submerged substrata can affect settlement of marine invertebrate larvae. We examined the effects of three species of bacteria, Deleya marina (Cobet et al.; Baumann et al.), Alteromonas macleodii Baumann et al. and Pseudomonas fluorescens Migula, on the attachment of cypris larvae of the barnacle Balanus amphitrite Darwin in laboratory assays. Bacterial cells or culture supernatant containing extracellular materials were allowed to adsorb to replicate sterile polystyrene petri dishes or borosilicate glass vials, and B. amphitrite cyprids were introduced to filmed and unfilmed (control) containers. Cells and supernatant from both log- and stationary-phase bacterial cultures were used in assays, which were repeated using different batches of larvae. Attachment of cyprids to control and filmed containers was monitored for several days. Cells and supernatant from stationary-phase cultures of D. marina consistently retarded cyprid attachment compared to attachment onto control polystyrene petri dishes, but not glass vials. Assays using films derived from log-phase D. marina cultures, and all assays with both log- and stationary-phase A. macleodii and P. fluorescens films, yielded weak and inconsistent effects on cyprid attachment. Despite variability among assays, bacterial effects on larval attachment within a particular assay generally were consistent for the duration of the assay (up to a week). Settlement was independent of the number of cyprids introduced to a container, within the range employed in assays. However, attachment of cyprids to control containers varied significantly among batches of barnacle larvae. Variation in results among assays may be related to variability in larval behavior, possibly explainable by larval diet.