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.     

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.     

Using ultraviolet light for improved antifouling performance on ship hull coatings

Abstract

A two-part study was designed to investigate the efficacy of using UVC to prevent biofouling in the context of ship hull coatings. The first study determined the frequency of UVC required for a coating that does not have any additives (epoxy). It was found that 1?min/day was effective at preventing hard fouling but not biofilm development. The second study addressed several variables: coating type (epoxy, copper, fouling release), frequency of UVC (no exposure, continuous exposure, 1min/6h, 1?min/day), and distance from the lamp (25 and 50?mm). Continuous UVC exposure resulted in no biofouling settlement but it did damage the copper coating. Intermittent UVC exposure was effective at preventing biofouling recruitment to both the copper and the fouling release coatings. Variations were observed with regards to the fouling composition, especially biofilms, sedimentary tubeworms and barnacles, suggesting tolerances within the community.     

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.     

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.     

Seasonal variations in the fouling diatom community structure from a monsoon influenced tropical estuary

Seasonal variations in the fouling diatom community from a monsoon influenced tropical estuary were investigated. The community composition did not differ significantly between stainless steel and polystyrene substrata due to dominance by Navicula spp. The experimental evidence suggests that Amphora, which is a dominant fouling diatom in temperate waters, ultimately dominates the community in tropical regions when conditions are favourable. These observations reveal that a faster onset of macrofouling interferes with the microfouling community wherein the faster recruiters that have a higher abundance in ambient waters, dominate the community. Seasonal variations were observed in the fouling diatom community. Navicula delicatula dominated during the post-monsoon and tychopelagic diatoms (Melosira and Odontella) were observed during the monsoon. Low diatom abundance was recorded during the pre-monsoon season. The results indicate that although the fouling diatom community composition does not vary between substrata, there is a seasonal change in the community depending on the physical, chemical and biological interactions.     

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.     

Biological succession on silicone fouling‐release surfaces: Long‐term exposure tests in the harbour of ischia,Italy

A static test site was set up in the Harbour of Ischia (Gulf of Naples, Italy) to investigate the antifouling effectiveness of newly developed non‐polluting coatings. Two‐year exposure experiments were performed on sets of panels coated with silicone‐based coatings, and results were compared both to sets of panels coated with toxic agents, and non‐toxic epoxydic compounds. Abiotic factors, strength of adhesion of the temporal dynamics of succession of foulers were analyzed throughout the period of immersion. Brown algae constantly represented the “border point”; between the early community, dominated by sume, micro‐ and macroalgae, and the late community, mainly represented by bryozoans and molluscs, as well as polychaetes, sponges and tunicates. Brown algae, such as Ectocarpus siliculosus, tunicates (mainly Botryllus schlossen) and polychaetes (Hydroides elegans, Pileolaria pseudomilitaris) were demonstrated to be key species, triggering the community and influencing its development. Light was the main abiotic factor discriminating the community on the two sides of panels exposed to different irradiances. The best performing coatings (silicone easy release coatings without additives) substantially influenced community structure, shifting it to the earliest stages of colonization. Silicone coatings proved to be unsuitable for colonization by organisms typical of mature communities, due to their low energy surfaces. The results of the present paper demonstrate that silicone coatings technology represents an alternative to the use of biocidal antifouling paints.     

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.     

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.     

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.     

A comparison of diatom community structure on natural and artificial substrata

Artificial substrata have been used in diatom studies for almost 100 years. However, concern still exists over whether diatom communities developing on artificial substrata accurately represent communities developing on natural substrata. This study compares the diatom communities colonising glass slides and clay tiles in two coastal dune lakes, and compares these communities to the naturally occurring communities in the epipelon, epilithon, and epiphyton. Both glass microslides and clay tiles, incubated for three separate periods ranging from 29 to 68 days, resulted in replicate substratum samples supporting similar diatom community compositions at each site. The degree of variation between artificial substrata communities at different sites, and between the two artificial substrata types, was generally no more than the degree of variation between communities on different types of natural substrata. Additionally, the composition of the diatom communities on the artificial substrata was representative of the community composition on the natural substrata. The effects of incubation period and siting are discussed.     

Effects of Detergents on in vitro Growth of Diatom Alga Thalassiosira pseudonana

The growth of the diatom alga Thalassiosira pseudonana was studied when exposed to an environment polluted by a detergent. We determined concentrations that inhibit cell division (10 mg/l) instead of algae growth (0.1 and 1 mg/l. It was shown that T. pseudonana can adapt to high detergent concentrations. The stimulation of the growth of Thalassiosira within a range of 0.03–0.08 mg/l concentration has been registered.     

A Phagomyxa-like Endoparasite of the Centric Marine Diatom Bellerochea malleus: A Phagotrophic Plasmodiophoromycete1

In September 1993 the marine centric diatom, Bellerochea malleus (Brightwell) Heurck, collected in the Wadden Sea near List/Sylt, was parasitized by a Phagomyxa algarum-like organism. Karling (1944) reported Phagomyxa algarum Karling in North Carolina as a parasite of the filamentous brown algae Ectocarpus and Pylaiella. The Bellerochea parasite develops an endocytoplasmic Plasmodium and incorporates host cytoplasm into a large, central digestion vacuole, by a form of phagocytosis. Later on, the Plasmodium cleaves to form a zoosporangiosorus. Each zoosporangium is surrounded by a thin wall. It releases zoospores (2.5 × 4 μm) with two unequal flagella, an anterior (4 μm long) and a posterior (8 μm long). Cystosori and cysts could not be detected. The ultrastructure of the zoosporangia and zoospores was investigated, with particular attention to the flagellar apparatus and its rearrangement during zoospore release. This process is very similar to that recorded for zoospores of the plasmodiophoromycete Polymyxa graminis Ledigham (Barr and Allan, 1982). The Bellerochea parasite is closely related to or identical with Phagomyxa algarum. The taxonomic position of Phagomyxa is discussed. In spite of its phagotrophic nutrition and the possible lack of cystosori and cysts, Phagomyxa should be regarded as a member of the Plasmodiophoromycota (or Plasmodiophorida) but not included in a separate order Phagomyxida as proposed by Cavalier-Smith (1993a).     

Activity of Commercial Enzymes on Settlement and Adhesion of Cypris Larvae of the Barnacle Balanus amphitrite,Spores of the Green Alga Ulva linza,and the Diatom Navicula perminuta

Fouling species produce adhesive polymers during the settlement, adhesion and colonization of new surfaces in the marine environment. The present paper tests the hypothesis that enzymes of the appropriate specificity may prevent biofouling by hydrolysing these adhesive polymers. Seventeen commercially available enzyme preparations designed originally for bulk use in a range of end-use applications were tested for their effects on the settlement and/or adhesion of three major fouling species, viz. the green alga Ulva linza, the diatom Navicula perminuta and the barnacle Balanus amphitrite. The serine-proteases were found to have the broadest antifouling potential reducing the adhesion strength of spores and sporelings of U. linza, cells of N. perminuta and inhibiting settlement of cypris larvae of B. amphitrite. Mode-of-action studies on the serine-protease, Alcalase, indicated that this enzyme reduced adhesion of U. linza in a concentration-dependent manner, that spores of the species could recover their adhesive strength if the enzyme was removed and that the adhesive of U. linza and juvenile cement of B. amphitrite became progressively less sensitive to hydrolysis as they cured.     

The effects of fine-scale substratum roughness on diatom community structure in estuarine biofilms

Benthic diatoms are a major component of biofilms that form on surfaces submerged in marine environments. Roughness of the underlying substratum affects the settlement of both diatoms and subsequent macrofouling colonizers. This study reports the effects of roughness on estuarine diatom communities established in situ in the Indian River Lagoon, FL, USA. Natural communities were established on acrylic panels with a range of surface roughnesses. Smoother substrata exhibited higher cell density, species richness, and diversity. Twenty-three of 58 species were found either exclusively or more abundantly on the smooth surfaces compared to one or both roughened treatments. The results suggest a greater ability of benthic diatoms to recruit and colonize smooth surfaces, which is probably explained by a higher degree of contact between the cells and the surface.     

Assessing scales of variability in benthic diatom community structure

Sources of variability such as sampling method, sample preparation, and sample analysis (taxonomy) might affect our ability to measure differences in community structure between sites in environmental effects studies. It is therefore important to ensure that changes in community structure related to the physical or chemical differences between sites are not hidden by other sources of variability within a site. The goal of this study was to quantify the amount of variability in benthic diatom community structure related to sampling and laboratory procedures. Our results showed that variability in community structure was minimal among replicate microscope slides (< 1%) and among samples collected within a site (1.8%). Variability in community structure was substantially higher between sites located in one stream (16.6%), and highest across streams (59.6%). This suggests that field sampling and laboratory methods do not contribute a large amount of variation into our analyses of benthic diatom community structure across sites.     

Periphyton growth and diatom community structure in a cooling water pond

Periphyton (Aufwuchs) accumulation was measured on artificial substrates in a pond in central Finland which receives warm cooling-water effluent from a power plant. The growth of periphyton was generally more rapid on the substrates during the first two weeks of colonization near the inflow of the warm water effluent than in the middle of the pond. The maximum accumulation of periphyton was in spring and autumn (dry weight maximum at warm effluent was in spring 3.5 mg DW cm⁻²,2.65 mg AFDW cm⁻²; chlorophyll a maximum 3.96 μg cm⁻² was found in autumn at pond-middle station). During mid-winter months the growth was strongly limited by solar radiation, but the growth was also slow at both stations in the summer months, when the power plant was out of operation. The periphyton accumulation rate was fastest near the water surface and decreased rapidly with increasing depth. A total of 167 diatom species were found in periphyton samples. However, most species were rare; many of the dominants were common to both plankton and periphyton. Species similarity analyses (Jaccard's similarity) between 10 different diatom communities (including periphyton from 9 different types of substrates and phytoplankton) indicated low similarity index values although differences between communities were not significant.     

Polysulfone and polyacrylate-based zwitterionic coatings for the prevention and easy removal of marine biofouling

A series of polysulfone and polyacrylate-based zwitterionic coatings were prepared on epoxy-primed aluminum substrata and characterized for their antifouling (AF) and fouling-release (FR) properties towards marine bacteria, microalgae and barnacles. The zwitterionic polymer coatings provided minimal resistance against bacterial biofilm retention and microalgal cell attachment, but facilitated good removal of attached microbial biomass by exposure to water-jet apparatus generated hydrodynamic shearing forces. Increasing the ion content of the coatings improved the AF properties, but required a stronger adhesive bond to the epoxy-primed aluminum substratum to prevent coating swelling and dissolution. Grafted poly(sulfobetaine) (gpSBMA), the most promising zwitterionic coating identified from microfouling evaluations, enabled the removal of four out of five barnacles reattached to its surface without incurring damage to their baseplates. This significant result indicated that gpSBMA relied predominately on its surface chemistry for its FR properties since it was very thin (~1–2 µm) relative to commercial coating standards (>200 µm).     

Biofilm diatom community structure: Influence of temporal and substratum variability

Abstract

Diatoms, which are early autotrophic colonisers, are an important constituent of the biofouling community in the marine environment. The effects of substratum and temporal variations on the fouling diatom community structure in a monsoon-influenced tropical estuary were studied. Fibreglass and glass coupons were exposed every month for a period of 4 days and the diatom population sampled at 24 h intervals, over a period of 14 months. The planktonic diatom community structure differed from the biofilm community. Pennate diatoms dominated the biofilms whilst centric diatoms were dominant in the water column. Among the biofilm diatoms, species belonging to the genera Navicula, Amphora, Nitzschia, Pleurosigma and Thalassionema were dominant. On certain occasions, the influence of planktonic blooms was also seen on the biofilm community. A comparative study of biofilms formed on the two substrata revealed significant differences in density and diversity. However species composition was almost constant. In addition to substratum variations, the biofilm diatom community structure also showed significant seasonal variations, which were attributed to physico-chemical and biological changes in both the water and substratum. Temporal variations in the tychopelagic diatoms of the water were also observed to exert an influence on the biofilm diatom community. Variations in diatom communities may determine the functional ecosystem of the benthic environment.