Settlement of benthic marine invertebrate larvae often limits recruitment, influencing the structure and dynamics of natural populations as well as biofouling of marine infrastructure, ship hulls, and aquaculture operations. Certain microbial components of substratum biofilms influence settlement (e.g. bacteria, diatoms), but the importance of biofilm protozoa has been unknown. We tested for effects of ciliates by comparing settlement and survival of common fouling invertebrates among 3 biofilm conditions: no biofilm, a purely bac terial biofilm, and a biofilm of bacteria and ciliates. With an assemblage of 7 ciliates (from Hypotrichia, Haptoria, and Scuticociliatia), the serpulid polychaete Galeolaria caespitosa showed a 44 to 49% average reduction in settlement rate compared to the purely bacterial biofilm, and post-settlement mortality increased 7-fold to 34%. In contrast, settlement and survival of the bryozoan Bugula neritina were unaffected. With a partially different assemblage of 11 ciliates (from Hypotrichia, Sticho trichia, Haptoria, Colpodida, and Scuticociliatia), settle ment of the serpulid Pomatoceros taeniata more than doubled, whereas that of the blue mussel Mytilus galloprovincialis was reduced by 54% compared to the purely bacterial biofilm. The results could not be explained by ciliates changing the total abundance of biofilm bacteria. We hypothesize that mechanisms could include direct interactions between larvae and ciliates (physical interactions, interference from ciliates' feeding currents, or responses to chemicals from ciliates), or indirect effects from ciliates altering the bacterial assemblage or its settlement cues. Such large and species-specific effects of ciliates on larval settlement and postsettlement mortality might impact invertebrate recruitment rates and species assemblages, especially because biofilm ciliates are highly variable over time and space.Aggregation of the tubeworm Galeolaria caespitosa. Larval settlement of these and other invertebrates is influenced by ciliates on the substratum.

Ciliate assemblages are often overlooked, but ubiquitous components of microbial biofilms which require a better understanding. Ciliate, diatom and bacterial colonisation were evaluated on two fouling-release (FR) coatings, viz. Intersleek 970 and Hempasil X3, and two biocidal antifouling (AF) coatings, viz. Intersmooth 360 and Interspeed 5640, in Port Phillip Bay, Australia. A total of 15 genera were identified during the 10 week deployment. Intersleek 970 displayed the most rapid fouling by ciliates, reaching 63.3(± 5.9) cells cm(-2). After 10 weeks, all four coatings were extensively fouled. However, the toxicity of the AF coatings still significantly inhibited microbial fouling compared to the FR coatings. On all treatments, colonies of sessile peritrichs dominated the ciliate assemblage in the early stage of succession, but as the biofilm matured, vagile ciliates exerted more influence on the assemblage structure. The AF coatings showed selective toxic effects, causing significant differences in the ciliate species assemblages among the treatments.

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Protozoan assemblages and successional dynamics are important components of biofouling that require better understanding. We studied marine ciliates in temperate Australia as they colonised artificial substrates for 21 d during 2 different seasons, with 2 different aspects of orientation. Sessile and planktonic taxa established within 7 d, whereas vagile taxa colonised throughout the period. Abundances reached 366 ciliates cm −2 . Colonies of the peritrichs Zoothamnium and Vorticella, and the hypotrichs Aspidisca and Euplotes were the most abundant. The north aspect received more light than the south aspect during summer, but assemblages did not differ significantly. Assemblage structure was different between seasons, and it developed more quickly and reached greater abundances during summer. A storm late in summer abruptly reduced abundances and affected functional groups differently, but diversity was largely unaffected. Thus, diversity of an established assemblage can be maintained through disturbances, despite abundances being subject to great fluctuation.

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