In the present study, 38 bacterial isolates were obtained from a marine biofilm, identified by the comparison of 16S rRNA gene sequences, and investigated by laboratory bioassays for their effects on larval settlement of the marine polychaete Hydroides elegans (Haswell). The bacterial isolates belonged to 3 phylogenetic branches: γ-Proteobacteria (26 isolates), Gram-positive (8 isolates) and Cytophaga-Flexibacter-Bacteroides (4 isolates). Most of the isolates were affiliated to the genera Vibrio (7 isolates), Alteromonas (8 isolates) or Pseudoalteromonas (8 isolates), which are in the γ-Proteobacteria branch. According to their efficacy to induce larval settlement of H. elegans in laboratory bioassays, the isolates were categorized as strongly, moderately, and non-inductive for larval settlement. About 42% of the isolates were categorized as non-inductive and the rest of the isolates contained equal numbers of highly and moderately inductive strains. The results indicated that larval settlement of H. elegans could be induced by bacteria in a wide range of taxa. The isolates that induced high and moderate levels of larval settlement belonged to the genus Cytophaga in the Cytophaga-Flexibacter-Bacteroides branch; the genera Bacillus, Brevibacterium, Micrococcus and Staphylococcus in the Gram-positive branch; and the genera Alteromonas, Pseudoalteromonas and Vibrio in the γ-Proteobacteria branch. Results also showed that isolates affiliating to the same genus might have tremendously different activities for the induction of larval settlement. For example, isolates that were affiliated to the genus Alteromonas or Pseudoalteromonas distributed over the 3 categories of activity for induction of larval settlement.
KEY WORDS: Hydroides elegans · Larval settlement · Biofilm · Bacteria · 16S rRNA genes
Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 226: [301][302][303][304][305][306][307][308][309][310] 2002 ment (i.e. attachment and metamorphosis) are wellknown examples for the secondary driving force.Surface-associated bacteria impose important influences over the settlement of many invertebrate larvae. Bacteria may stimulate (e.g. Szewzyk et al. 1991, Leitz & Wagner 1993, Lau & Qian 1997, Unabia & Hadfield 1999, inhibit (e.g. Holmström et al. 1992, Avelin et al. 1993, Lau & Qian 2000 or not affect (e.g. Brancato & Woollacott 1982, Avelin et al. 1993, Lau & Qian 1997, Unabia & Hadfield 1999) larval settlement, depending on the species of invertebrates and bacteria of concern. Although the presence of surface-associated bacteria is a prerequisite for larval settlement of certain invertebrates, larvae of these invertebrates may respond to individual bacterial isolates to different extents (Kirchman et al. 1982, Lau & Qian 1997, Unabia & Hadfield 1999. Previous studies have suggested the effect of surface-associated bacterial communities on larval settlement to be a function of bacterial species composition (Keough & Raimondi 1996, Lau & Qian 1997, Rodriguez & E...
