Static vs dynamic settlement and adhesion of diatoms to ship hull coatings

Seasonal variation in the biological succession of marine diatoms over 316L stainless steel in a coastal environment of Chile

Characterizing seasonal changes in diatom community profiles in coastal environments is scarce worldwide. Despite diatoms being prevalent in microfouling, their role in microbially influenced corrosion of metallic materials remains poorly understood. This study reports the effect of seasonal variations on the settlement of marine diatoms and corrosion of 316 L stainless steel surfaces exposed to Chilean coastal seawater. Electron microscopy imaging revealed a diverse assembly of diatoms, exhibiting pronounced differences at genus level between summer and winter seasons, with a significant delay in diatom settlement during winter. Electrochemical measurements indicated an active role of diatoms in increasing corrosion current during biofilm development. While the final diatom composition was similar irrespective of the season, the analyses of diatom assemblages over time differed, showing faster colonization when silicate and nitrate were available. This study lays the foundation for future research on the dominant season-specific genera of diatoms to unveil the microbial interactions that could contribute to corrosion and to evaluate their potential as bioindicators for alternative surveillance strategies.

Disturbance frequency directs microbial community succession in marine biofilms exposed to shear

IMPORTANCE

Disturbances are major drivers of community succession in many microbial systems; however, relatively little is known about marine biofilm community succession, especially under antifouling disturbance. Antifouling technologies exert strong local disturbances on marine biofilms, and resulting biomass losses can be accompanied by shifts in biofilm community composition and succession. We address this gap in knowledge by bridging microbial ecology with antifouling technology development. We show that disturbance by shear can strongly alter marine biofilm community succession, acting as a selective filter influenced by frequency of exposure. Examining marine biofilm succession patterns with and without shear revealed stable associations between key prokaryotic and eukaryotic taxa, highlighting the importance of cross-domain assessment in future marine biofilm research. Describing how compounded top-down and bottom-up disturbances shape the succession of marine biofilms is valuable for understanding the assembly and stability of these complex microbial communities and predicting species invasiveness.

Impact of hydrodynamics on community structure and metabolic production of marine biofouling formed in a highly energetic estuary

Biofouling is a specific lifestyle including both marine prokaryotic and eukaryotic communities. Hydrodynamics are poorly studied parameters affecting biofouling formation. This study aimed to investigate how water dynamics in the Etel Estuary (Northwest Atlantic coasts of France) influences the colonization of artificial substrates. Hydrodynamic conditions, mainly identified as shear stress, were characterized by measuring current velocity, turbulence intensity and energy using Acoustic Doppler Current Profiler (ADCP). One-month biofouling was analyzed by coupling metabarcoding (16S rRNA, 18S rRNA and COI genes), untargeted metabolomics (liquid chromatography coupled with high-resolution mass spectrometry, LC-HRMS) and characterization of the main biochemical components of the microbial exopolymeric matrix. A higher richness was observed for biofouling communities (prokaryotes and eukaryotes) exposed to the strongest currents. Ectopleura (Cnidaria) and its putative symbionts Endozoicomonas (Gammaproteobacteria) were dominant in the less dynamic conditions. Eukaryotes assemblages were specifically shaped by shear stress, leading to drastic changes in metabolite profiles. Under high hydrodynamic conditions, the exopolymeric matrix increased and was composed of 6 times more polysaccharides than proteins, these latter playing a crucial role in the adhesion and cohesion properties of biofilms. This original multidisciplinary approach demonstrated the importance of shear stress on both the structure of marine biofouling and the metabolic response of these complex communities.

Development of Antifouling Strategies for Marine Applications

Marine biofouling is an undeniable challenge for aquatic systems since it is responsible for several environmental and ecological problems and economic losses. Several strategies have been developed to mitigate fouling-related issues in marine environments, including developing marine coatings using nanotechnology and biomimetic models, and incorporating natural compounds, peptides, bacteriophages, or specific enzymes on surfaces. The advantages and limitations of these strategies are discussed in this review, and the development of novel surfaces and coatings is highlighted. The performance of these novel antibiofilm coatings is currently tested by in vitro experiments, which should try to mimic real conditions in the best way, and/or by in situ tests through the immersion of surfaces in marine environments. Both forms present their advantages and limitations, and these factors should be considered when the performance of a novel marine coating requires evaluation and validation. Despite all the advances and improvements against marine biofouling, progress toward an ideal operational strategy has been slow given the increasingly demanding regulatory requirements. Recent developments in self-polishing copolymers and fouling-release coatings have yielded promising results which set the basis for the development of more efficient and eco-friendly antifouling strategies.

Boundary layer hydrodynamics of patchy biofilms

Algal biofilms, ubiquitous in aquatic systems, reduce the performance of engineered systems and alter ecosystem processes. Biofilm morphology is dynamic throughout community development, with patchiness occurring due to periodic sloughing, but little is known about how community level physical structure affects hydrodynamics. This study uses high resolution particle image velocimetry (PIV) to examine spatially explicit turbulence over sparse, uniform and patchy biofilm at turbulent Reynolds numbers. All biofilms increase the near-bed turbulence production, Reynolds shear stress, and rotational flow compared to a smooth wall, and non-uniform biofilms have the greatest increase in these parameters, compared with a uniform or sparse biofilm. However, a higher drag coefficient over uniform biofilm compared with non-uniform biofilm indicates that percent coverage (the amount of area covered by the biofilm) is a useful predictor of a biofilm's relative effect on the total drag along surfaces, and in particular the effect on ship performance.

On the mechanism of marine fouling-prevention performance of oil-containing silicone elastomers

For many decades, silicone elastomers with oil incorporated have served as fouling-release coating for marine applications. In a comprehensive study involving a series of laboratory-based marine fouling assays and extensive global field studies of up to 2-year duration, we compare polydimethylsiloxane (PDMS) coatings of the same composition loaded with oil via two different methods. One method used a traditional, one-pot pre-cure oil addition approach (o-PDMS) and another method used a newer post-cure infusion approach (i-PDMS). The latter displays a substantial improvement in biofouling prevention performance that exceeds established commercial silicone-based fouling-release coating standards. We interpret the differences in performance between one-pot and infused PDMS by developing a mechanistic model based on the Flory–Rehner theory of swollen polymer networks. Using this model, we propose that the chemical potential of the incorporated oil is a key consideration for the design of future fouling-release coatings, as the improved performance is driven by the formation and stabilization of an anti-adhesion oil overlayer on the polymer surface.

High-throughput method development for in-situ quantification of aquatic phototrophic biofilms

In the maritime field where biofouling has both economic and environmental impacts, in situ quantification methods of biofilm development are of outstanding importance. Indeed, it is challenging to temporally monitor biofilm formation due to the complexity of the marine ecosystem, common inaccessibility of sampling location and lack of standardized techniques. Here, an artificial polymeric surface was tested in situ and in vitro against natural phototrophic biofilms and monoculture biofilms using plate reader fluorescence. The suitability of the developed method was verified using fluorescence microscopy coupled with image analysis - a common quantification technique - demonstrating a strong correlation between the tested methods. The results indicated the efficiency of inherent chlorophyll fluorescence in quantifying undisturbed phototrophic biofilms in field and laboratory conditions using microplate reader. This work demonstrated that the suggested approach is promising for biofilm high-throughput testing, and therefore has the potential to be used in several research and industrial sectors for monitoring phototrophic biofilm development.

Seawater copper content controls biofilm bioaccumulation and microbial community on microplastics

The adsorption of trace metals on microplastics (MPs) is affected by the presence of surficial biofilms but their interactions are poorly understood. Here, we present the influence of Cu levels in real seawater (Toulon Bay, NW Mediterranean Sea) on microbial communities and Cu content of the resulting biofilms grown during incubation experiments on high density polyethylene. Two sets of incubation experiments were run with seawater supplied with MPs, sampled in two sites with contrasting Cu levels: Pt12 (most contaminated site) and Pt41P (less contaminated site). For each incubation experiment, 5 treatments were considered differing in Cu concentrations, ranging between 30 and 400 nM and between 6 and 60 nM, for Pt12 and Pt41p, respectively. A control experiment (filtered at 0.2 μm) was run in parallel for each incubation experiment. We observed that, at the time scale of the incubation period, both prokaryotic and eukaryotic richness and diversity were higher in the biofilms formed from the most contaminated site. In addition, we showed that Cu levels are shaping biofilm communities, evidencing co-occurrence patterns between prokaryotes and eukaryotes with diatoms playing a central role. These differences in biofilm formation were reflected in the amount of bioaccumulated Cu per dry weight of MPs, exhibiting higher values in the most contaminated site. Within this site, the increase of Cu seawater content enhanced its bioaccumulation onto MPs until reaching saturation. This study strongly suggests a striking link between seawater copper content, biofilm community shaping and the resulting Cu bioaccumulation onto MPs.

Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments

The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between -0.3 V and 0.3 V or between -0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials.

Crawling and adhesion behavior of Halamphora sp. based on different parts of Folium Sennae-like film: Evaluation of analytical methods for anti-diatom experimental results

Anti-diatom testing is a basic method to evaluate the anti-fouling performance of coatings. Many existing results of anti-diatom performances are evaluated based on their attachment number or coverage area, ignoring the influence of the crawling and adhesion behavior of diatoms on the analysis results. Here, a Folium Sennae-like film with multiple structural units was prepared by considering the influence of diatom attachment behaviors on the analysis results. The anti-diatom performances of different parts (divided and called four parts: edge, surface, cross striation, and vertical pattern) on the Folium Sennae-like film were evaluated using the counting and area methods. Obviously, the anti-diatom performance of the Folium Sennae-like film was superior to that of epoxy resin without structure. Under equal areas, the average numbers of diatoms on the cross striation and the vertical pattern were similar to the surface. It was found that the attachment behavior of Halamphora sp. is affected by microstructure units, rather than the combined structure of which the scale is much larger than that of diatoms. Meanwhile, the average attachment area for the unit number of diatoms was calculated. The diatom attachment area without microstructure, surface, cross striation, or vertical pattern was 81.751, 106.950, 73.904, and 84.376 μm², respectively. Moreover, the static and dynamic motion behaviors of Halamphora sp. were studied, and the theory for Halamphora sp. attachment was modeled in three dimensions. The variable morphology of Halamphora sp. lead to inaccurate results for diatom analyses based on the counting and area methods, which is summarized here. This study discusses the evaluation method of coatings by anti-diatom performance, further promoting the research of diatoms in the field of antifouling.

Influence of light and flow on taxon composition and photosynthesis of marine phototrophic biofilm in photobioreactors

In this study, marine biofilms were cultured in a flow-lane, semi-continuous photobioreactor at different irradiances and flows to evaluate their combined effect on biofilms' phototrophic composition and photosynthetic activity. Taxon richness, evaluated by different microscopy techniques, including transmission and scanning electron microscopy, resulted to be heavily reduced from source communities to mature cultures. The strongest decrease was observed for diatoms, which were overcome by cyanobacteria and green algae over time. Photosynthetic performance was investigated by pulse amplitude modulated fluorescence. Irradiance was the main driver of data distribution of the photosynthetic parameters rel.ETR_max and I_k, while flow rate affected α and ΔF/F_m'. The combination of irradiance and flow rate affected ΔF/F_m' reflecting the photosynthetic performance of the most relatively abundant taxa. Higher ΔF/F_m' was attained when cyanobacteria and green algae were dominating, whilst lower ΔF/F_m' when diatoms occurred in the initial phase of biofilm development.

An automated image analysis platform for the study of weakly -adhered cells

Details of the design and implementation of an open-source platform for studying the adhesion of cells attached to solid substrata are provided. The hardware is based on a laser-cut flow channel connected to a programmable syringe pump. The software automates all aspects of the flow rate profile, data acquisition and image analysis. An example of the pelagic diatom Thalassiosira rotula adhered to poly(dimethyl siloxane) surfaces is provided. The procedure described enables the shear rate to be converted to drag force for arbitrary-shaped objects, of utility to the study of many cell species, especially ones that are obviously non-spherical. It was determined that 90% of cells are removed with the application of drag forces < 3×10-12 N, and that this value is relatively independent of the incubation time on the surface. This result is important to understand how marine species interact with polymer surfaces that are used in electrical insulator applications.

Impacts of a temperate to tropical voyage on the microalgal hull fouling community of an atypically-operated vessel

Microalgal communities that colonize the hulls of at-risk vessels - those which have the highest port residency times, lowest speeds, and most stationary time in water - are expected to change as a function of environmental factors during ocean voyages, but are rarely studied. The microalgal communities on the hull of an atypically operated ship, the T.S. Golden Bear, were quantified during the course of a voyage from San Francisco Bay to the South Pacific and back. Here we clearly demonstrate that microalgal communities can be highly resilient, and can survive physiologically strenuous journeys through extreme variation in salinity and temperature. A 42% reduction in microalgal biomass and a 62% reduction in algal cellular abundance indicated a community-wide negative reaction to an increase in both salinity and temperature after the ship left San Francisco Bay, CA and cruised southward to Long Beach, although in vivo cellular fluorescence capacity increased. Further reductions in biomass (36%) and cellular abundance (26%) occurred once the ship encountered high-temperature, high-salinity waters in Hawaii. A 17% reduction of cellular fluorescence capacity was also observed in Hawaii. Despite previous environmental stressors, upon return to temperate waters off Vallejo, CA, biomass increased 230%, cellular abundance remained stable, and cellular fluorescence capacity increased from 0.45 ± 0.26 to 0.60 ± 0.07. The methods used in the current research provide efficient, cost-effective procedures for analyzing microalgal (and macrofouling) communities, which can in turn aid regulators in creating such necessary thresholds for enforcement.

Effects of 'in-service' conditions - mimicked hull roughness ranges and biofilms - on the surface and the hydrodynamic characteristics of foul-release type coatings

To develop a better understanding of 'in-service' performance of modern marine coatings, this study explored the combined effects of different roughness ranges of foul-release coating (FRC) and light biofouling (slime) on the surface, boundary layer and drag characteristics under a range of 'in-service' conditions. Natural and laboratory biofilms were grown dynamically on FRC panels by exposing panels in facilities dedicated to realistic fouling culture. The boundary layer experiments were conducted in a circulating water tunnel. Boundary layer similarity-law scaling was used to predict the combined effects of coating roughness and biofilms on the added frictional resistance (% ΔCF) and added required effective power  (%ΔPE ) for a benchmark KRISO container ship (KCS) and a bulk carrier. The increase in  %ΔPE  due to the presence of biofilms on commercial FRC is estimated to be between 7% and 16% depending on the biofilm type, biofilm thickness and percentage coverage. Significant increases in effective power are estimated for non-fouling control primers with heavy fouling. Moreover, the paper suggests updated roughness allowances ( ΔCF ) for two vessel types assuming FRCs on their hulls with more representative hull roughness ranges and fluffy biofilms.

Marine Antibiofouling Properties of TiO2 and Ti-Cu-O Films Deposited by Aerosol-Assisted Chemical Vapor Deposition

The actual interest in developing light-induced catalytic coatings to act as an antibiofouling alternative has recently prompted interest in the incorporation of Cu into TiO2 films, working as a visible light sensitizer catalyst. TiO2 and new Ti-Cu-O films with Cu contents ranging between 16% and 75% Cu/(Cu + Ti) are deposited by aerosol-assisted metalorganic chemical vapor deposition at a substrate temperature of 550 °C. The films are composed of TiO2 anatase phase, mixed with Cu2O when including Cu in the composition. Pure TiO2 films’ morphologies are characterized by the formation of microflower-like structures with nanometric petals, which induce a high specific surface. These features are not present in Ti-Cu-O films. A UV-Visible study revealed that the optical band gap energy decreases with increasing Cu content. Interestingly, Ti-Cu-O films presented a highly photo-catalytic activity in the orange-G degradation. Marine biofouling field tests in Lorient’s Harbor in France and in vitro tests were carried out in order to evaluate the antifouling performance of the films, revealing that topography and chemical composition can act differently on different species. Field tests revealed that TiO2 microflowers reduced the fouling coverage. Besides, Ti-Cu-O films with 16 at.% Cu presented lower fouling coverage than films containing 58 at.% Cu. In vitro tests using two diatoms (P. tricornutum and N. perminuta) showed that the spaces between microflowers play a significant role in the adhesion of diatoms: microalgae adhere less when spaces are bigger than their cells, compared to when spaces are of the same size as cells. Films containing Cu did not alter N. perminuta growth nor adhesion, while they affected P. tricornutum by lowering its growth rate and adhesion without noticeable toxicity. Indeed, Cu-Ti-O is a very promising non-toxic fouling release film for marine and industrial applications.

Ship hull in-water cleaning and its effects on fouling-control coatings

Today, ship hull fouling is managed through fouling-control coatings, complemented with in-water cleaning. During cleaning, coating damage and wear must be avoided, for maximum coating lifetime and reduced antifoulant release. When possible, cleaning should target early stages of fouling, using minimal forces. However, such forces, and their effects on coatings, have not yet been fully quantified. In this one-year study, minimal cleaning forces were determined using a newly-designed immersed waterjet. The results show that bi-monthly/monthly cleaning, with maximum wall shear stress up to ∼1.3 kPa and jet stagnation pressure ∼0.17 MPa, did not appear to cause damage or wear on either the biocidal antifouling (AF) or the biocide-free foul-release (FR) coatings. The AF coating required bi-monthly cleanings to keep fouling to incipient slime (time-averaged results), while the FR coating had a similar fouling level even without cleaning. The reported forces may be used in matching cleaning parameters to the adhesion strength of the early stages of fouling.

Shear Stress as a Major Driver of Marine Biofilm Communities in the NW Mediterranean Sea

While marine biofilms depend on environmental conditions and substrate, little is known about the influence of hydrodynamic forces. We tested different immersion modes (dynamic, cyclic and static) in Toulon Bay (north-western Mediterranean Sea; NWMS). The static mode was also compared between Toulon and Banyuls Bays. In addition, different artificial surfaces designed to hamper cell attachment (self-polishing coating: SPC; and fouling-release coating: FRC) were compared to inert plastic. Prokaryotic community composition was affected by immersion mode, surface characteristics and site. Rhodobacteriaceae and Flavobacteriaceae dominated the biofilm community structure, with distinct genera according to surface type or immersion mode. Cell density increased with time, greatly limited by hydrodynamic forces, and supposed to delay biofilm maturation. After 1 year, a significant impact of shear stress on the taxonomic structure of the prokaryotic community developed on each surface type was observed. When surfaces contained no biocides, roughness and wettability shaped prokaryotic community structure, which was not enhanced by shear stress. Conversely, the biocidal effect of SPC surfaces, already major in static immersion mode, was amplified by the 15 knots speed. The biofilm community on SPC was 60% dissimilar to the biofilm on the other surfaces and was distinctly colonized by Sphingomonadaceae ((Alter)Erythrobacter). At Banyuls, prokaryotic community structures were more similar between the four surfaces tested than at Toulon, due possibly to a masking effect of environmental constraints, especially hydrodynamic, which was greater than in Toulon. Finally, predicted functions such as cell adhesion confirmed some of the hypotheses drawn regarding biofilm formation over the artificial surfaces tested here.

Marine biofilms: diversity of communities and of chemical cues

Surfaces immersed in seawater are rapidly colonized by various microorganisms, resulting in the formation of heterogenic marine biofilms. These communities are known to influence the settlement of algae spores and invertebrate larvae, triggering a succession of fouling events, with significant environmental and economic impacts. This review covers recent research regarding the differences in composition of biofilms isolated from different artificial surface types and the influence of environmental factors on their formation. One particular phenomenon - bacterial quorum sensing (QS) - allows bacteria to coordinate swarming, biofilm formation among other phenomena. Some other marine biofilm chemical cues are believed to modulate the settlement and the succession of macrofouling organisms, and they are also reviewed here. Finally, since the formation of a marine biofilm is considered to be an initial, QS-dependent step in the development of marine fouling events, QS inhibition is discussed on its potential as a tool for antibiofouling control in marine settings.

Cell Shape and Surface Colonisation in the Diatom Genus Cocconeis-An Opportunity to Explore Bio-Inspired Shape Packing?

Optimal packing of 2 and 3-D shapes in confined spaces has long been of practical and theoretical interest, particularly as it has been discovered that rotatable ellipses (or ellipsoids in the 3-D case) can, for example, have higher packing densities than disks (or spheres in the 3-D case). Benthic diatoms, particularly those of the genus Cocconeis (Ehr.)-which are widely regarded as prolific colonisers of immersed surfaces-often have a flattened (adnate) cell shape and an approximately elliptical outline or "footprint" that allows them to closely contact the substratum. Adoption of this shape may give these cells a number of advantages as they colonise surfaces, such as a higher packing fraction for colonies on a surface for more efficient use of limited space, or an increased contact between individual cells when cell abundances are high, enabling the cells to minimize energy use and maximize packing (and biofilm) stability on a surface. Here, the outline shapes of individual diatom cells are measured using scanning electron and epifluorescence microscopy to discover if the average cell shape compares favourably with those predicted by theoretical modelling of efficient 2-D ellipse packing. It is found that the aspect ratio of measured cells in close association in a biofilm-which are broadly elliptical in shape-do indeed fall within the range theoretically predicted for optimal packing, but that the shape of individual diatoms also differ subtly from that of a true ellipse. The significance of these differences for optimal packing of 2-D shapes on surfaces is not understood at present, but may represent an opportunity to further explore bio-inspired design shapes for the optimal packing of shapes on surfaces.

Polyurethane, epoxy resin and polydimethylsiloxane altered biofilm formation and mussel settlement

In many environments, biofilms are a major mode and an emergent form of microbial life. Biofilms play crucial roles in biogeochemical cycling and invertebrate recruitment in marine environments. However, relatively little is known about how marine biofilms form on different substrata and about how these biofilms impact invertebrate recruitment. Here, we performed a comparative analysis of a 28-day-old biofilm community on non-coated (a control glass) and coated substrata (polyurethane (PU), epoxy resin (EP) and polydimethylsiloxane (PDMS)) and examined the settlement of Mytilus coruscus plantigrades on these biofilms. PU, EP and PDMS deterred the development of marine biofilms by reducing the biofilm biomass including the biofilm dry weight, cell density of the bacteria and diatoms and chlorophyll a concentrations. Further analysis of bacterial community revealed that EP altered the bacterial community composition compared with that on the glass substrata by reducing the relative abundance of Ruegeria (Alphaproteobacteria) and by increasing the relative abundance of Methylotenera (Betaproteobacteria) and Cyanobacteria in the biofilms. However, bacterial communities developed on PU and PDMS, as well as glass and PU, EP and PDMS did not exhibit differences from each other. The M. coruscus settlement rates on biofilms on PU, EP and PDMS were reduced by 20-41% compared with those on the glass after 28 days. Thus, the tested coatings impacted the development of marine biofilms by altering the biofilm biomass and/or the bacterial community composition. The mussel settlements decreased in the biofilms that formed on the coatings compared with those on non-coated glass.

PYRROLO isolated from marine sponge associated bacterium Halobacillus kuroshimensis SNSAB01 - Antifouling study based on molecular docking, diatom adhesion and mussel byssal thread inhibition

In the present study, an attempt has been made to explore the antifouling potential of bioactive compound isolated from sponge associated bacterium Halobacillus kuroshimensis SNSAB01. The crude extract of SNSAB01 strongly inhibited the growth of fouling bacterial strains with least minimal inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The bioactive compound was characterized through FT-IR, HPLC, GCMS and NMR predicted as 'pyrrolo". From the mass spectral library, structure was elucidated as pyrrolo [1, 2-a] pyrazine-1, 4-dione, hexahydro. The in silico studies provided encouraging docking scores with two interactions by GLN 200 and GLU 304. The extract inhibited 89% diatom adhesion at 350 μg/ml concentration against Amphora sp. An EC₅₀ value of 150 μg/ml for 50% inhibition of byssal thread of Perna viridis and LC₅₀ was found to be 500 μg/ml. The LC₅₀/EC₅₀ ratio of 3.0 indicated nontoxic to nature. The result suggested that pyrrolo[1,2-a]pyrazine-1,4-dione can be used for antifouling coating.

Roughness effects of diatomaceous slime fouling on turbulent boundary layer hydrodynamics

Biofilm fouling significantly impacts ship performance. Here, the impact of biofilm on boundary layer structure at a ship-relevant, low Reynolds number was investigated. Boundary layer measurements were performed over slime-fouled plates using high resolution particle image velocimetry (PIV). The velocity profile over the biofilm showed a downward shift in the log-law region (ΔU⁺), resulting in an effective roughness height (k_s) of 8.8 mm, significantly larger than the physical thickness of the biofilm (1.7 ± 0.5 mm) and generating more than three times as much frictional drag as the smooth-wall. The skin-friction coefficient, C_f, of the biofilm was 9.0 × 10^-3 compared with 2.9 × 10^-3 for the smooth wall. The biofilm also enhances turbulent kinetic energy (tke) and Reynolds shear stress, which are more heterogeneous in the streamwise direction than smooth-wall flows. This suggests that biofilms increase drag due to high levels of momentum transport, likely resulting from protruding streamers and surface compliance.

Parallelized microfluidic diatom accumulation assay to test fouling-release coatings

Assessing the efficiency of the next generation of protective marine coatings is highly relevant for their optimization. In this paper, a parallelized microfluidic testing device is presented to quantify the accumulation of a model organism (Navicula perminuta) under constant laminar flow. Using automated microscopy in conjunction with image analysis, the adhesion densities on the tested surfaces could be determined after exposure to a flow of suspended algae for 90 min. The optimized protocol for the assay is presented, and the reproducibility of the densities of attached diatoms was verified on four identical surfaces (self-assembled dodecanethiol monolayers). A set of well-characterized self-assembled monolayers with different chemical terminations was used to validate the performance of the assay and its capability to discriminate diatom accumulation on different surface chemistries under dynamic conditions. The observed trends are in good agreement with previously published results obtained in single channel accumulation and detachment assays. To demonstrate the practical relevance of the dynamic experiment, diatom attachment on four technically relevant silicone coatings with different fouling-release properties could clearly be distinguished.

Dynamic field testing of coating chemistry candidates by a rotating disk system

Quick and reliable testing is crucial for the development of new fouling release (FR) coatings. Exposure of these coatings to natural multispecies communities is essential in evaluating their efficacy. To this end, we present a rotating disk setup for dynamic field exposure. To achieve a well-defined flow on the surface of the disk, an easy to use sample mounting system was developed that provides a smooth and even surface. We related the angular velocity of the disk to the wall shear stress on the surface with a hydrodynamic model. The wall shear stress was adjusted to values previously found to be suitable to discriminate dynamic diatom attachment on different coating chemistries in the lab. The effect of the dynamic conditions was shown by comparing polystyrene slides under static and dynamic exposure. Using a set of self-assembled monolayers, the discrimination potential of the assay in a multispecies environment was demonstrated.

Comparative study of biofilm formation on biocidal antifouling and fouling-release coatings using next-generation DNA sequencing

The bacterial and eukaryotic communities forming biofilms on six different antifouling coatings, three biocidal and three fouling-release, on boards statically submerged in a marine environment were studied using next-generation sequencing. Sequenced amplicons of bacterial 16S ribosomal DNA and eukaryotic ribosomal DNA internal transcribed spacer were assigned taxonomy by comparison to reference databases and relative abundances were calculated. Differences in species composition, bacterial and eukaryotic, and relative abundance were observed between the biofilms on the various coatings; the main difference was between coating type, biocidal compared to fouling-release. Species composition and relative abundance also changed through time. Thus, it was possible to group replicate samples by coating and time point, indicating that there are fundamental and reproducible differences in biofilms assemblages. The routine use of next-generation sequencing to assess biofilm formation will allow evaluation of the efficacy of various commercial coatings and the identification of targets for novel formulations.

A multi-step approach for testing non-toxic amphiphilic antifouling coatings against marine microfouling at different levels of biological complexity

Marine biofouling on artificial surfaces such as ship hulls or fish farming nets causes enormous economic damage. The time for the developmental process of antifouling coatings can be shortened by reliable laboratory assays. For designing such test systems, it is important that toxic effects can be excluded, that multiple parameters can be addressed simultaneously and that mechanistic aspects can be included. In this study, a multi-step approach for testing antifouling coatings was established employing photoautotrophic biofilm formation of marine microorganisms in micro- and mesoscoms. Degree and pattern of biofilm formation was determined by quantification of chlorophyll fluorescence. For the microcosms, co-cultures of diatoms and a heterotrophic bacterium were exposed to fouling-release coatings. For the mesocosms, a novel device was developed that permits parallel quantification of a multitude of coatings under defined conditions with varying degrees of shear stress. Additionally, the antifouling coatings were tested for leaching of potential compounds and finally tested in sea trials. This multistep-approach revealed that the individual steps led to consistent results regarding antifouling activity of the coatings. Furthermore, the novel mesocosm system can be employed for advanced antifouling analysis including metagenomic approaches for determination of microbial diversity attaching to different coatings under changing shear forces.

Biofilm community structure and the associated drag penalties of a groomed fouling release ship hull coating

Grooming is a proactive method to keep a ship's hull free of fouling. This approach uses a frequent and gentle wiping of the hull surface to prevent the recruitment of fouling organisms. A study was designed to compare the community composition and the drag associated with biofilms formed on a groomed and ungroomed fouling release coating. The groomed biofilms were dominated by members of the Gammaproteobacteria and Alphaproteobacteria as well the diatoms Navicula, Gomphonemopsis, Cocconeis, and Amphora. Ungroomed biofilms were characterized by Phyllobacteriaceae, Xenococcaceae, Rhodobacteraceae, and the pennate diatoms Cyclophora, Cocconeis, and Amphora. The drag forces associated with a groomed biofilm (0.75 ± 0.09 N) were significantly less than the ungroomed biofilm (1.09 ± 0.06 N). Knowledge gained from this study has helped the design of additional testing which will improve grooming tool design, minimizing the growth of biofilms and thus lowering the frictional drag forces associated with groomed surfaces.

Topographic cues guide the attachment of diatom cells and algal zoospores

Surface topography plays a key role in the colonization of substrata by the colonizing stages of marine fouling organisms. For the innovation of marine antifouling coatings, it is essential to understand how topographic cues affect the settlement of these organisms. In this study, tapered, spiked microstructures and discrete honeycombs of varying feature dimensions were designed and fabricated in order to examine the influence of topography on the attachment of zoospores of the green macroalga Ulva linza and cells of the diatom (microalga) Navicula incerta. Contrasting results were obtained with these two species of algae. Indeed, the preferred location of cells of N. incerta was dominated by attachment point theory, which suggested a positive correlation between the density of cells adhering and the amount of available attachment points, while the settlement of spores of U. linza was mainly regulated by both Wenzel roughness and local binding geometry.

Microfluidic accumulation assay probes attachment of biofilm forming diatom cells

Testing of fouling release (FR) technologies is of great relevance for discovery of the next generation of protective marine coatings. In this paper, an accumulation assay to test diatom interaction under laminar flow with the model organism Navicula perminuta is introduced. Using time lapse microscopy with large area sampling allows determination of the accumulation kinetics of the diatom on three model surfaces with different surface properties at different wall shear stresses. The hydrodynamic conditions within the flow cell are described and a suitable shear stress range to perform accumulation experiments is identified at which statistically significant discrimination of surfaces is possible. The observed trends compare well to published adhesion preferences of N. perminuta. Also, previously determined trends of critical wall shear stresses required for cell removal from the same set of functionalized interfaces shows consistent trends. Initial attachment mediated by extracellular polymeric substances (EPS) present outside the diatoms leads to the conclusion that the FR potential of the tested coating candidates can be deducted from dynamic accumulation experiments under well-defined hydrodynamic conditions. As well as testing new coating candidates for their FR properties, monitoring of the adhesion process under flow provides additional information on the mechanism and geometry of attachment and the population kinetics.

Diatom communities on commercial biocidal fouling control coatings after one year of immersion in the marine environment

Little is known about the effect of commercial biocidal fouling control coatings on fouling diatom communities and their growth forms after long periods of exposure in the marine tropical environment. The current study investigated the abundance and composition of fouling diatom communities developed on 11 commercially available biocidal antifouling coatings, covering the three main technology types in recent historic use (Self-Polishing Copolymers, Self-Polishing Hybrid and Controlled Depletion Polymers) after one year of static immersion at two locations in Muscat, Oman (Marina Shangri La and Marina Bandar Rowdha). Light microscopy demonstrated that the total abundance of diatoms and the relative abundance of growth forms were significantly affected by the choice of biocidal antifouling coating and experimental location. Using scanning electron microscopy, a total of 21 diatom genera were identified which were grouped into adnate, motile, plocon and erect growth forms. The adnate growth forms, mainly the genera Amphora, Cocconeis and Mastogloia, dominated the other growth forms in terms of their relative abundance. Current results revealed the importance of exposure location and choice of biocidal antifouling coating on the relative abundance of diatom growth forms.

Diagnosis of the Diatom Community upon Biofilm Development on Stainless Steels in Natural Freshwater

This paper reports the development of biofilms on stainless steels (SS) upon exposure in a natural freshwater ecosystem for about six months and focuses on the composition of diatom populations. By using environmental scanning electron microscopy (ESEM) technique, we provide a detailed description regarding diatom identification at species level as well as their main characteristics, including type, morphology, ability to form colony, and motility. Results reveal the presence of both prostrate (initial colonizers) and stalked (late colonizers) forms. Pennate diatoms, Cocconeis placentula and Amphora coffeaeformis, and a centric diatom, Melosira varians, are shown to be the abundant forms regardless of the SS type. Pennate diatoms dominate the community and are directly attached to the substratum, whereas the centric form is entangled in the biofilm matrix in a significant number. The dominance of adnate forms suggests that these cells are sturdy and successfully maintaining their population. In situ monitoring of the electrochemical response of immersed materials showed ennoblement of the open circuit potential, which seems to be due to the biogenic production of H₂O₂, detected in a significant amount within the biofilms. The substantial enrichment of biofilms with diatoms potentially suggests the implication of these microorganisms in the process of ennoblement. A mechanism is proposed in this paper describing the possible interactions of diatom community with SS in the studied ecosystem.

Transported biofilms and their influence on subsequent macrofouling colonization

Biofilm organisms such as diatoms are potential regulators of global macrofouling dispersal because they ubiquitously colonize submerged surfaces, resist antifouling efforts and frequently alter larval recruitment. Although ships continually deliver biofilms to foreign ports, it is unclear how transport shapes biofilm microbial structure and subsequent macrofouling colonization. This study demonstrates that different ship hull coatings and transport methods change diatom assemblage composition in transported coastal marine biofilms. Assemblages carried on the hull experienced significant cell losses and changes in composition through hydrodynamic stress, whereas those that underwent sheltered transport, even through freshwater, were largely unaltered. Coatings and their associated biofilms shaped distinct macrofouling communities and affected recruitment for one third of all species, while biofilms from different transport treatments had little effect on macrofouling colonization. These results demonstrate that transport conditions can shape diatom assemblages in biofilms carried by ships, but the properties of the underlying coatings are mainly responsible for subsequent macrofouling. The methods by which organisms colonize and are transferred by ships have implications for their distribution, establishment and invasion success.

Influence of Biodegradable Polymer Properties on Antifouling Paints Activity

The development of new antifouling paints requires understanding the parameters involved in antifouling activity and to develop new analytical tools for their evaluation. A series of biodegradable poly(ε-caprolactone-co-δ-valerolactone) copolymers varying by molecular weight and composition were synthesized, characterized and formulated as antifouling paints. The physico-chemical properties such as hydration, degradation, erosion and lixiviation of paints were studied. Microfouling (bacteria and microalgae) was observed by microscopic observations in a short delay, whereas macrofouling colonization was observed by visual inspection during one year. The antifouling activity of paints was modified by varying the composition and molecular weight of copolymer. The crystallinity appears to play a major role in antifouling activity, however the involvement of other properties such as hydration, degradation or erosion remains difficult to understand. Confocal laser scanning and scanning electron microscopes were used for the evaluation of antifouling paints. Results show that microalgae seem to be a pertinent indicator of antifouling activity.

Influence of hydrodynamic stress on the frictional drag of biofouling communities

The role of hydrodynamic wall shear stresses on the development of the fouling community structure and resulting frictional drag were examined using a commercially available fouling release coating. Immersed test panels were exposed to three different hydrodynamic treatments, one static and two dynamic (corresponding to an estimated wall shear stress of 7.0  and 25.5 Pa). The drag of the panels was measured in a hydrodynamic test chamber at discrete time intervals over 35 days. The fouling community composition on the static panels was significantly different from the organisms observed on the dynamic panels. Despite different fouling community composition, the drag forces measured on the panels were very similar. This suggests that the frictional drag of low form and soft fouling communities are similar and that there may be a stepwise increase in frictional drag associated with the presence of mature calcareous organisms.

A new diatom growth inhibition assay using the XTT colorimetric method

Marine biofouling, which leads to significant operational stress and economic damage on marine infrastructures, is a major problem in marine related industries. Currently, the most common way to avoid marine biofouling involves the use of biocidal products in surface coatings. However, the need for environmentally friendly antibiofouling compounds has increased rapidly with the recent global prohibition of harmful antifoulants, such as tributyltin (TBT). In particular, periphytic diatoms have been shown to contribute significantly to biofilms, which play an important role in biofouling. Therefore, inhibiting the proliferation of fouling diatoms is a very important step in the prevention of marine biofouling. In this study, we developed a new, rapid, accurate, and convenient growth inhibition assay using the XTT colorimetric method to prevent the growth of the fouling periphytic diatom, Nitzschia amabilis Hidek. Suzuki (replaced synonym, Nitzschia laevis Hustedt). The feasibility of this method was verified by determining the growth inhibition activities of two standard photosynthetic inhibitors, DCMU and CuSO4. However, neither inhibitor had any cytotoxic activities at the range of concentrations tested. Moreover, this method was applied by screening and purification of herbicidic but non-cytotoxic compounds from cyanobacteria extracts. Our results demonstrate the utility of this newly established growth inhibition assay for the identification of marine anti-biofouling compounds.

Analysis of mechanical grooming at various frequencies on a large scale test panel coated with a fouling-release coating

A mechanical grooming test was performed on large scale steel test panels coated with a fouling-release (FR) coating (International Intersleek 900), at four different frequencies, during the high fouling season in Port Canaveral, Florida. Grooming at frequencies of three or two times per week was effective at removing heavy biofilm growth and significantly reduced macrofouling settlement. Mechanical grooming at lower frequencies of weekly or bi-weekly removed heavy biofilm growth but was much less effective at reducing macrofouling settlement. The results indicated that frequent mechanical grooming could reduce the fouling rating of ships coated with FR coatings. The reduction in the fouling rating of ships' hulls by frequent grooming could offer significant reductions in drag, fuel consumption, and the emission of exhaust gases. Frequent grooming could also eliminate the need for hull cleaning and increase the time between dry docking which would reduce the operational costs for many vessel operators.

Quorum sensing is a language of chemical signals and plays an ecological role in algal-bacterial interactions

Algae are ubiquitous in the marine environment, and the ways in which they interact with bacteria are of particular interest in marine ecology field. The interactions between primary producers and bacteria impact the physiology of both partners, alter the chemistry of their environment, and shape microbial diversity. Although algal-bacterial interactions are well known and studied, information regarding the chemical-ecological role of this relationship remains limited, particularly with respect to quorum sensing (QS), which is a system of stimuli and response correlated to population density. In the microbial biosphere, QS is pivotal in driving community structure and regulating behavioral ecology, including biofilm formation, virulence, antibiotic resistance, swarming motility, and secondary metabolite production. Many marine habitats, such as the phycosphere, harbour diverse populations of microorganisms and various signal languages (such as QS-based autoinducers). QS-mediated interactions widely influence algal-bacterial symbiotic relationships, which in turn determine community organization, population structure, and ecosystem functioning. Understanding infochemicals-mediated ecological processes may shed light on the symbiotic interactions between algae host and associated microbes. In this review, we summarize current achievements about how QS modulates microbial behavior, affects symbiotic relationships, and regulates phytoplankton chemical ecological processes. Additionally, we present an overview of QS-modulated co-evolutionary relationships between algae and bacterioplankton, and consider the potential applications and future perspectives of QS.

Dual hydrophilic and salt responsive schizophrenic block copolymers – synthesis and study of self-assembly behavior

Block copolymers undergoing conversion from “conventional” to “inverse” micelles upon changing the medium are described.

Superhydrophobic resistance to dynamic freshwater biofouling inception

Superhydrophobic nanotextured surfaces have gained increased usage in various applications due to their non-wetting and self-cleaning abilities. The aim of this study was to investigate nanotextured surfaces with respect to their resistance to the inception of freshwater biofouling at transitional flow conditions. Several coatings were tested including industry standard polyurethane (PUR), polytetrafluoroethylene (PTFE), capstone mixed polyurethane (PUR + CAP) and nanocomposite infused polyurethane (PUR + NC). Each surface was exposed to freshwater conditions in a lake at 4 m s(-1) for a duration of 45 min. The polyurethane exhibited the greatest fouling elements, in terms of both height and number of elements, with the superhydrophobic nanocomposite based polyurethane (PUR + NC) showing very little to no fouling. A correlation between the surface characteristics and the degree of fouling inception was observed.

Holographic microscopy provides new insights into the settlement of zoospores of the green alga Ulva linza on cationic oligopeptide surfaces

Interaction of zoospores of Ulva linza with cationic, arginine-rich oligopeptide self-assembled monolayers (SAMs) is characterized by rapid settlement. Some spores settle (ie permanently attach) in a 'normal' manner involving the secretion of a permanent adhesive, retraction of the flagella and cell wall formation, whilst others undergo 'pseudosettlement' whereby motile spores are trapped (attached) on the SAM surface without undergoing the normal metamorphosis into a settled spore. Holographic microscopy was used to record videos of swimming zoospores in the vicinity of surfaces with different cationic oligopeptide concentrations to provide time-resolved insights into processes associated with attachment of spores. The data reveal that spore attachment rate increases with increasing cationic peptide content. Accordingly, the decrease in swimming activity in the volume of seawater above the surface accelerated with increasing surface charge. Three-dimensional trajectories of individual swimming spores showed a 'hit and stick' motion pattern, exclusively observed for the arginine-rich peptide SAMs, whereby spores were immediately trapped upon contact with the surface.

Grooming using rotating brushes as a proactive method to control ship hull fouling

Grooming may be defined as the frequent and gentle cleaning of a ship hull coating, when it is in port or idle, to prevent the establishment of fouling. This study assessed the effectiveness of grooming with a five-headed rotating brush system on epoxy, ablative copper and two silicone fouling release (FR) coatings. These coatings were placed under static immersion at Port Canaveral, FL on a weekly and biweekly frequency. The results showed that grooming reduced fouling on all surfaces and was able to prevent fouling on the ablative copper and FR coatings when performed weekly. It was concluded that the grooming tool used for these tests was sufficient to remove biofilm and most hard fouling. However, when fouling pressure increased or when grooming was performed less frequently, insufficient forces were imparted by the brush to remove all of the established hard fouling organisms.

Combinatorial materials research applied to the development of new surface coatings XVI: fouling-release properties of amphiphilic polysiloxane coatings

High-throughput methods were used to prepare and characterize the fouling-release (FR) properties of an array of amphiphilic polysiloxane-based coatings possessing systematic variations in composition. The coatings were derived from a silanol-terminated polydimethylsiloxane, a silanol-terminated polytrifluorpropylmethylsiloxane (CF3-PDMS), 2-[methoxy(polyethyleneoxy)propyl]-trimethoxysilane (TMS-PEG), methyltriacetoxysilane and hexamethyldisilazane-treated fumed silica. The variables investigated were the concentration of TMS-PEG and the concentration of CF3-PDMS. In general, it was found that the TMS-PEG and the CF3-PDMS had a synergist effect on FR properties with these properties being enhanced by combining both compounds into the coating formulations. In addition, reattached adult barnacles removed from coatings possessing both TMS-PEG and relatively high levels of CF3-PDMS displayed atypical base-plate morphologies. The majority of the barnacles removed from these coatings exhibited a cupped or domed base-plate as compared to the flat base-plate observed for the control coating that did not contain TMS-PEG or CF3-PDMS. Coating surface analysis using water contact angle measurements indicated that the presence of CF3-PDMS facilitated migration of TMS-PEG to the coating/air interface during the film formation/curing process. In general, coatings containing both TMS-PEG and relatively high levels of CF3-PDMS possessed excellent FR properties.

Dynamic surface deformation of silicone elastomers for management of marine biofouling: laboratory and field studies using pneumatic actuation

Many strategies have been developed to improve the fouling release (FR) performance of silicone coatings. However, biofilms inevitably build on these surfaces over time. Previous studies have shown that intentional deformation of silicone elastomers can be employed to detach biofouling species. In this study, inspired by the methods used in soft-robotic systems, controlled deformation of silicone elastomers via pneumatic actuation was employed to detach adherent biofilms. Using programmed surface deformation, it was possible to release > 90% of biofilm from surfaces in both laboratory and field environments. A higher substratum strain was required to remove biofilms accumulated in the field environment as compared with laboratory-grown biofilms. Further, the study indicated that substratum modulus influences the strain needed to de-bond biofilms. Surface deformation-based approaches have potential for use in the management of biofouling in a number of technological areas, including in niche applications where pneumatic actuation of surface deformation is feasible.

Impact of diatomaceous biofilms on the frictional drag of fouling-release coatings

Skin-friction results are presented for fouling-release (FR) hull coatings in the unexposed, clean condition and after dynamic exposure to diatomaceous biofilms for 3 and 6 months. The experiments were conducted in a fully developed turbulent channel flow facility spanning a wide Reynolds number range. The results show that the clean FR coatings tested were hydraulically smooth over much of the Reynolds number range. Biofilms, however, resulted in an increase in skin-friction of up to 70%. The roughness functions for the biofilm-covered surfaces did not display universal behavior, but instead varied with the percentage coverage by the biofilm. The effect of the biofilm was observed to scale with its mean thickness and the square root of the percentage coverage. A new effective roughness length scale (keff) for biofilms based on these parameters is proposed. Boundary layer similarity-law scaling is used to predict the impact of these biofilms on the required shaft power for a mid-sized naval surface combatant at cruising speed. The increase in power is estimated to be between 1.5% and 10.1% depending on the biofilm thickness and percentage coverage.

Microfluidic detachment assay to probe the adhesion strength of diatoms

Fouling release (FR) coatings are increasingly applied as an environmentally benign alternative for controlling marine biofouling. As the technology relies on removing fouling by water currents created by the motion of ships, weakening of adhesion of adherent organisms is the key design goal for improved coatings. In this paper, a microfluidic shear force assay is used to quantify how easily diatoms can be removed from surfaces. The experimental setup and the optimization of the experimental parameters to study the adhesion of the diatom Navicula perminuta are described. As examples of how varying the physico-chemical surface properties affects the ability of diatoms to bind to surfaces, a range of hydrophilic and hydrophobic self-assembled monolayers was compared. While the number of cells that attached (adhered) was barely affected by the coatings, the critical shear stress required for their removal from the surface varied significantly.

Antifouling properties of oligo(lactose)-based self-assembled monolayers

The antifouling (AF) properties of oligo(lactose)-based self-assembled monolayers (SAMs), using four different proteins, zoospores of the green alga Ulva linza and cells of the diatom Navicula incerta, were investigated. The SAM-forming alkylthiols, which contained 1, 2 or 3 lactose units, showed significant variation in AF properties, with no differences in wettability. Non-specific adsorption of albumin and pepsin was low on all surfaces. Adsorption of lysozyme and fibrinogen decreased with increasing number of lactose units in the SAM, in agreement with the generally observed phenomenon that thicker hydrated layers provide higher barriers to protein adsorption. Settlement of spores of U. linza followed an opposite trend, being greater on the bulkier, more hydrated SAMs. These SAMs are more ordered for the larger saccharide units, and it is therefore hypothesized that the degree of order, and differences in crystallinity or stiffness between the surfaces, is an important parameter regulating spore settlement on these surfaces.

Analysis of long-term mechanical grooming on large-scale test panels coated with an antifouling and a fouling-release coating

Long-term grooming tests were conducted on two large-scale test panels, one coated with a fluorosilicone fouling-release (FR) coating, and one coated with a copper based ablative antifouling (AF) coating. Mechanical grooming was performed weekly or bi-weekly using a hand operated, electrically powered, rotating brush tool. The results indicate that weekly grooming was effective at removing loose or heavy biofilm settlement from both coatings, but could not prevent the permanent establishment of low-profile tenacious biofilms. Weekly grooming was very effective at preventing macrofouling establishment on the AF coating. The effectiveness of weekly grooming at preventing macrofouling establishment on the FR coating varied seasonally. The results suggest that frequent mechanical grooming is a viable method to reduce the fouling rating of ships' hulls with minimal impact to the coating. Frequent grooming could offer significant fuel savings while reducing hull cleaning frequencies and dry dock maintenance requirements.

Colonisation and succession of marine biofilm-dwelling ciliate assemblages on biocidal antifouling and fouling-release coatings in temperate Australia

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.