Diatom community structure on commercially available ship hull coatings

Diatoms are primary colonizers of both antifouling and fouling-release ship hull coatings. There are few published studies which report on diatom community development on modern ship hull coatings. This study reports diatom communities on eight commercial marine ship hull coatings exposed at three static immersion sites along the east coast of Florida, viz. Daytona, Sebastian, and Miami. The coatings tested were three ablative copper systems (Ameron ABC-3, International BRA-640, and Hempel Olympic 76600), two copper-free biocidal systems (E-Paint SN-1, Sherwin Williams HMF), and three fouling-release (FR) systems (International Intersleek 700, International Intersleek 900, and Hempel Hempasil). One hundred and twenty-seven species comprising 44 genera were identified, including some of the more commonly known foulers, viz. Achnanthes, Amphora, Cocconeis, Entomoneis, Licmophora, Melosira, Navicula, Nitzschia, Synedra, and Toxarium. A significant difference was seen among sites, with the more estuarine site, Sebastian, having lower overall diatom abundance and higher diversity than Daytona and Miami. Copper coatings were primarily fouled by Amphora delicatissima and Entomoneis pseudoduplex. Copper-free coatings were fouled by Cyclophora tenuis, A. delicatissima, Achnanthes manifera, and Amphora bigibba. FR surfaces were typified by C. tenuis, and several species of Amphora. The presence of C. tenuis is new to the biofouling literature, but as new coatings are developed, this diatom may be one of many that prove to be problematic for static immersion. Results show coatings can be significantly influenced by geographical area, highlighting the need to test ship hull coatings in locations similar to where they will be utilized.     

Diatom community structure on in-service cruise ship hulls

Diatoms are an important component of marine biofilms found on ship hulls. However, there are only a few published studies that describe the presence and abundance of diatoms on ships, and none that relate to modern ship hull coatings. This study investigated the diatom community structure on two in-service cruise ships with the same cruise cycles, one coated with an antifouling (AF) system (copper self-polishing copolymer) and the other coated with a silicone fouling-release (FR) system. Biofilm samples were collected during dry docking from representative areas of the ship and these provided information on the horizontal and vertical zonation of the hull, and intact and damaged coating and niche areas. Diatoms from the genera Achnanthes, Amphora and Navicula were the most common, regardless of horizontal ship zonation and coating type. Other genera were abundant, but their presence was more dependent on the ship zonation and coating type. Samples collected from damaged areas of the hull coating had a similar community composition to undamaged areas, but with higher diatom abundance. Diatom fouling on the niche areas differed from that of the surrounding ship hull and paralleled previous studies that investigated differences in diatom community structure on static and dynamically exposed coatings; niche areas were similar to static immersion and the hull to dynamic immersion. Additionally, diatom richness was greater on the ship with the FR coating, including the identification of several new genera to the biofouling literature, viz. Lampriscus and Thalassiophysa. These results are the first to describe diatom community composition on in-service ship hulls coated with a FR system. This class of coatings appears to have a larger diatom community compared to copper-based AF systems, with new diatom genera that have the ability to stick to ship hulls and withstand hydrodynamic forces, thus creating the potential for new problematic species in the biofilm.     

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

Many experiments utilize static immersion tests to evaluate the performance of ship hull coatings. These provide valuable data; however, they do not accurately represent the conditions both the hull and fouling organisms encounter while a ship is underway. This study investigated the effect of static and dynamic immersion on the adhesion and settlement of diatoms to one antifouling coating (BRA 640), four fouling-release coatings (Intersleek^® 700, Intersleek^® 900, Hempasil X3, and Dow Corning 3140) and one standard surface (Intergard^® 240 Epoxy). Differences in community composition were observed between the static and dynamic treatments. Achnanthes longipes was present on all coatings under static immersion, but was not present under dynamic immersion. This was also found for diatoms in the genera Bacillaria and Gyrosigma. Melosira moniformis was the only diatom present under dynamic conditions, but not static conditions. Several common fouling diatom genera were present on panels regardless of treatment: Amphora, Cocconeis, Entomoneis Cylindrotheca, Licmophora, Navicula, Nitzschia, Plagiotropis, and Synedra. Biofilm adhesion, diatom abundance and diatom diversity were found to be significantly different between static and dynamic treatments; however, the difference was dependent on coating and sampling date. Several coatings (Epoxy, DC 3140 and IS 700) had significantly higher biofilm adhesion on dynamically treated panels on at least one of the four sampling dates, while all coatings had significantly higher diatom abundance on at least one sampling date. Diversity was significantly greater on static panels than dynamic panels for Epoxy, IS 700 and HX3 at least once during the sampling period. The results demonstrate how hydrodynamic stress will significantly influence the microfouling community. Dynamic immersion testing is required to fully understand how antifouling surfaces will respond to biofilm formation when subjected to the stresses experienced by a ship underway.     

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.     

The development of marine biofilms on two commercial non-biocidal coatings: a comparison between silicone and fluoropolymer technologies

The antimicrobial performance of two fouling-release coating systems, Intersleek 700? (IS700; silicone technology), Intersleek 900? (IS900; fluoropolymer technology) and a tie coat (TC, control surface) was investigated in a short term (10 days) field experiment conducted at a depth of ca 0.5 m in the Marina Bandar Rawdha (Muscat, Oman). Microfouling on coated glass slides was analyzed using epifluorescence microscopy and adenosine-5'-triphosphate (ATP) luminometry. All the coatings developed biofilms composed of heterotrophic bacteria, cyanobacteria, seven species of diatoms (2 species of Navicula, Cylindrotheca sp., Nitzschia sp., Amphora sp., Diploneis sp., and Bacillaria sp.) and algal spores (Ulva sp.). IS900 had significantly thinner biofilms with fewer diatom species, no algal spores and the least number of bacteria in comparison with IS700 and the TC. The ATP readings did not correspond to the numbers of bacteria and diatoms in the biofilms. The density of diatoms was negatively correlated with the density of the bacteria in biofilms on the IS900 coating, and, conversely, diatom density was positively correlated in biofilms on the TC. The higher antifouling efficacy of IS900 over IS700 may lead to lower roughness and thus lower fuel consumption for those vessels that utilise the IS900 fouling-release coating.     

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.     

Temporal and spatial variation in the fouling of silicone coatings in Pearl Harbor, Hawaii

An antifouling or foul-release coating cannot be globally effective if it does not perform well in a range of environmental conditions, against a diversity of fouling organisms. From 1996 to 1998, the field test sites participating in the United States Navy's Office of Naval Research 6.2 Biofouling program examined global variation in the performance of 3 silicone foul-release coatings, viz. GE RTV11, Dow Corning RTV 3140, and Intersleek (International Coatings Ltd), together with a control anticorrosive coating (Ameron Protective Coatings F-150 series). At the University of Hawaii's test site in Pearl Harbor, significant differences were observed among the coatings in the rate of accumulation of fouling. The control coating failed rapidly; after 180-220 d immersion a community dominated by molluscs and sponges developed that persisted for the remainder of the experiment. Fouling of the GE and Dow Corning silicone coatings was slower, but eventually reached a similar community structure and coverage as the control coatings. The Intersleek coating remained lightly fouled throughout the experiment. Spatial variation in the structure of the community fouling the coatings was observed, but not in the extent of fouling. The rate of accumulation of fouling reflected differences among the coatings in adhesion of the tubeworm Hydroides elegans. The surface properties of these coatings may have affected the rate of fouling and the structure of the fouling community through their influence on larval settlement and subsequent interactions with other residents, predators, and the physical environment.     

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.     

Poly(dimethyl siloxane) (PDMS) network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)-fluoroalkyl side chains for fouling-release coatings. II. Laboratory assays and field immersion trials

Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700?. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.     

Poly(dimethyl siloxane) (PDMS) network blends of amphiphilic acrylic copolymers with poly(ethylene glycol)-fluoroalkyl side chains for fouling-release coatings. II. Laboratory assays and field immersion trials

Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700?. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.     

Phenotypic variation for adhesive tenacity in the barnacle Balanus amphitrite

Silicone fouling-release coatings represent a non-toxic alternative to biocide-containing ship hull paints. These coatings allow fouling organisms to attach to the hull surface, but prevent firm adhesion. Adhesive tenacity to fouling-release materials varies both among and within species. We quantified broad-sense genetic and environmental sources of intraspecific variation in tenacity to two silicone substrata, for the barnacle Balanus amphitrite. For both materials tenacity varied over an order of magnitude; however, the partitioning of this variation differed between the substrata. For International Veridian, a commercially-available fouling-release coating, removal stress varied significantly among maternal families and replicate barnacle cultures. Variation among the maternal families was associated with previously observed differences among these families in the condition of the adhesive plaque. Additional experiments suggested that variation among the replicate cultures arose from heterogeneity between replicate coatings in properties that affect tenacity. We could not attribute variation in removal stress for Dow Corning Silastic T-2, a silicone rubber used for mold-making, to any of the genetic or environmental sources tested. Instead, variation may have been due to measurement error or heterogeneity within replicate coatings in properties affecting tenacity. Differences among maternal families in removal stress may stem from variation in the interaction between the adhesive and the substratum, or in the viscoelastic properties of the adhesive plaque.     

The development of marine biofilms on two commercial non-biocidal coatings: a comparison between silicone and fluoropolymer technologies

The antimicrobial performance of two fouling-release coating systems, Intersleek 700® (IS700; silicone technology), Intersleek 900® (IS900; fluoropolymer technology) and a tie coat (TC, control surface) was investigated in a short term (10 days) field experiment conducted at a depth of ca 0.5 m in the Marina Bandar Rawdha (Muscat, Oman). Microfouling on coated glass slides was analyzed using epifluorescence microscopy and adenosine-5′-triphosphate (ATP) luminometry. All the coatings developed biofilms composed of heterotrophic bacteria, cyanobacteria, seven species of diatoms (2 species of Navicula, Cylindrotheca sp., Nitzschia sp., Amphora sp., Diploneis sp., and Bacillaria sp.) and algal spores (Ulva sp.). IS900 had significantly thinner biofilms with fewer diatom species, no algal spores and the least number of bacteria in comparison with IS700 and the TC. The ATP readings did not correspond to the numbers of bacteria and diatoms in the biofilms. The density of diatoms was negatively correlated with the density of the bacteria in biofilms on the IS900 coating, and, conversely, diatom density was positively correlated in biofilms on the TC. The higher antifouling efficacy of IS900 over IS700 may lead to lower roughness and thus lower fuel consumption for those vessels that utilise the IS900 fouling-release coating.     

Development of the initial diatom microfouling layer on antifouling and fouling-release surfaces in temperate and tropical Australia

Diatoms are a major component of the slime layers that form on artificial surfaces in marine environments. In this article, the role played by diatoms during the pioneering stages of colonization of three marine antifouling (AF) coatings, viz Intersmooth 360®, Super Yacht 800® and a fouling-release (FR) coating Intersleek 700®, was investigated. The study was conducted over three distinct seasons in two very different marine environments in Australia, ie temperate Williamstown, Victoria and tropical Cairns, Queensland. Diatom fouling occurred more rapidly on the FR coating Intersleek 700, compared to both biocidal AF paints. However, colonization by diatoms on all three coatings was generally slow during the 16-day study. Benthic diatoms do not subsist by floating around in the water column, rather they only gain the opportunity to colonize new surfaces when they either voluntarily release or are displaced from their benthic habitat, thereafter entering the water column where the opportunity to adhere to a new surface presents itself. However, once settled, fouling diatoms grow exponentially from the site of attachment, spreading out until they populate large areas of the surface. This mode of surface colonization correlates more with an ‘infection’ type, epidemiology model, a mechanism that accounts for the colonization of significant regions of the coating surface from a single fouling diatom cell, forming ‘clonal patches’. This is in comparison to the bacterial colonization of the surface, which exhibits far more rapid recruitment and growth of cells on the substratum surface. Therefore, it is hypothesized that fouling diatoms may be characterized more by their ability to adhere and grow on surfaces already modified by bacterial biofilms, rather than on their strength of adhesion. Cell morphology and the ability to avoid shear may also be an important factor.     

A preliminary study on the properties and fouling-release performance of siloxane-polyurethane coatings prepared from poly(dimethylsiloxane) (PDMS) macromers

Siloxane-polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol?1) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.     

A preliminary study on the properties and fouling-release performance of siloxane–polyurethane coatings prepared from poly(dimethylsiloxane) (PDMS) macromers

Siloxane–polyurethane fouling-release (FR) coatings based on aminopropyl terminated poly(dimethylsiloxane) (PDMS) macromers were prepared and characterized for FR performance via laboratory biological assays. These systems rely on self-stratification, resulting in a coating with a siloxane-rich surface and polyurethane bulk. Previously, these coating systems have used PDMS with multiple functional groups which react into the polyurethane bulk. Here, aminopropyl terminated PDMS macromers were prepared, where a single amine group anchors the PDMS in the coating. Coatings were prepared with four molecular weights (1000, 5000, 10,000, and 15,000 g mol^?1) and two levels of PDMS (5% and 10%). High water contact angles and low surface energies were observed for the coatings before and after water immersion, along with low pseudobarnacle removal forces. Laboratory bioassays showed reduced biofilm retention of marine bacteria, good removal of diatoms from coatings with low molecular weight PDMS, high removal of algal sporelings (young plants), and low removal forces of live barnacles.     

Diatoms of the Puck Bay coastal shallows (Poland, Southern Baltic)

In the study area 150 diatom taxa were identified, including several varieties. The characteristic feature of the community is the strong predominance of several epipsammic diatom species of which Achnanthes delicatula, Fragilaria construens var. venter, Navicula cryptolyra , and Opephora olsenii are the most abundant. The predominating taxa are autochthonous in the study area and their percent content ranges from 70 to 90%. In the sediments studied there was also a large group of species which are typical of the Puck Bay interior. They are usually represented by several specimens showing various degrees of destruction. Only few of them attain in the study area considerable percent contents e.g. Achnanthes lemmermanni, Amphora acutiuscula, Cocconeis scutellum, Diploneis interrupta, Navicula rhynchocephala, N. perminuta, Nitzschia frustulum and N. nana. Numerous taxa reported in the paper are recorded in the study area for the first time.     

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.     

Quantitative exploration of the contribution of settlement,growth, dispersal and grazing to the accumulation of natural marine biofilms on antifouling and fouling-release coatings

The accumulation of microbial biofilms on ships’ hulls negatively affects ship performance and efficiency while also playing a role in the establishment of even more detrimental hard-fouling communities. However, there is little quantitative information on how the accumulation rate of microbial biofilms is impacted by the balance of the rates of cell settlement, in situ production (ie growth), dispersal to surrounding waters and mortality induced by grazers. These rates were quantified on test panels coated with copper-based antifouling (AF) or polymer-based fouling-release (FR) coatings by using phospholipids as molecular proxies for microbial biomass. The results confirmed the accepted modes of efficacy of these two types of coatings. In a more extensive set of experiments with only the FR coatings, it was found that seasonally averaged cellular production rates were 1.5 ± 0.5 times greater than settlement and the dispersal rates were 2.7 ± 0.8 greater than grazing. The results of this study quantitatively describe the dynamic balance of processes leading to the accumulation of microbial biofilm on coatings designed for ships’ hulls.     

Marine anti-biofouling efficacy of amphiphilic poly(coacrylate) grafted PDMSe: effect of graft molecular weight

There is currently strong motivation due to ecological concerns to develop effective anti-biofouling coatings that are environmentally benign, durable, and stable for use by the maritime industry. The antifouling (AF) and fouling-release (FR) efficacy of amphiphilic, charged copolymers composed of ~52% acrylamide, ~34% acrylic acid, and ~14% methyl acrylate grafted to poly(dimethyl siloxane) (PDMSe) surfaces were tested against zoospores of the green alga Ulva linza and the diatom Navicula incerta. The biofouling response to molecular weight variation was analyzed for grafts ranging from ~100 to 1,400 kg mol^?1, The amphiphilic coatings showed a marked improvement in the FR response, with a 55% increase in the percentage removal of diatoms and increased AF efficacy, with 92% reduction in initial attachment density of zoospores, compared to PDMSe controls. However, graft molecular weight, in the range tested, was statistically insignificant. Grafting copolymers to PDMSe embossed with the Sharklet? microtopography did not produce enhanced AF efficacy.     

Combinatorial materials research applied to the development of new surface coatings IX: an investigation of novel antifouling/fouling-release coatings containing quaternary ammonium salt groups

Polysiloxane coatings containing chemically-bound ("tethered") quaternary ammonium salt (QAS) moieties were investigated for potential application as environmental-friendly coatings to control marine biofouling. A combinatorial/high-throughput approach was applied to the investigation to enable multiple variables to be probed simultaneously and efficiently. The variables investigated for the moisture-curable coatings included QAS composition, ie alkyl chain length, and concentration as well as silanol-terminated polysiloxane molecular weight. A total of 75 compositionally unique coatings were prepared and characterized using surface characterization techniques and biological assays. Biological assays were based on two different marine microorganisms, a bacterium, Cellulophaga lytica and a diatom, Navicula incerta, as well as a macrofouling alga, Ulva. The results of the study showed that all three variables influenced coating surface properties as well as antifouling (AF) and fouling-release (FR) characteristics. The incorporation of QAS moieties into a polysiloxane matrix generally resulted in an increase in coating surface hydrophobicity. Characterization of coating surface morphology revealed a heterogeneous, two-phase morphology for many of the coatings investigated. A correlation was found between water contact angle and coating surface roughness, with the contact angle increasing with increasing surface roughness. Coatings based on the QAS moiety containing the longest alkyl chain (18 carbons) displayed the highest micro-roughness and, thus, the most hydrophobic surfaces. With regard to AF and FR properties, coatings based on the 18 carbon QAS moieties were very effective at inhibiting C. lytica biofilm formation and enabling easy removal of Ulva sporelings (young plants) while coatings based on the 14 carbon QAS moities were very effective at inhibiting biofilm growth of N. incerta.