Ultrastructural observations on the marine fouling diatomAmphora

Ecological and Scanning electron microscope (S. E. M.) studies indicated that the diatomAmphora was an important constituent in the initial colonization of test panels coated with a copper antifouling composition.Amphora was also found as the dominant fouling diatom species on paint samples from in-service supertankers and yachts. Associated with the diatom was copious amounts of mucilaginous material, which often encapsulated the cells. Histochemical analysis of the mucilage indicates that it is predominantly polysaccharide in nature. Using the Transmission electron microscope (T. E. M.) and electron microscope cytochemistry the intracellular origin of the adhesive was investigated. T. E. M. and S. E. M. observations of acid-cleaned-cells indicate that the mucilage may be secreted through specialized regions of the frustule. Material isolated from antifouling panels was compared with laboratory culturedAmphora spp. for copper resistance and internal accumulation using TEMSCAN — X ray analytical equipment.     

The influence of natural surface microtopographies on fouling

Multiple antifouling strategies of marine organisms may consist of combinations of physical, chemical and mechanical mechanisms. In this study, the role of surface microtopography (< 500 microns) of different marine organisms, such as Cancer pagurus, Mytilus edulis, Ophiura texturata and the eggcase of Scyliorhinus canicula, has been investigated as a possible component of their defence systems. High resolution resin replicates of these natural surface structures were exposed to natural fouling in field experiments. Abundances of recruits were determined and compared to those on untextured, but otherwise identical, control surfaces to quantify the influence of the different microtopographies on fouling rates. Antifouling effects of microtopographies varied with type of microtopography and coloniser species. The surface microtopography of C. pagurus significantly rejected macrofoulers. The surface structures of the eggcase and O. texturata had repellent effects on microfoulers. Barnacle settlement was temporarily reduced on surface microtopographies of M. edulis and the eggcase. These results emphasise the promising nontoxic antifouling properties of microtextured surfaces.     

Observations on the mechanisms of attachment of some marine fouling blue-green algae

Using scanning electron microscopy (SEM), differential interference contrast microscopy (DICM) and cytochemical staining techniques, preliminary observations have been made on the mechanisms of attachment of some common, marine, benthic fouling blue-green algae ("cyanobacteria") isolated into culture from various toxic and non-toxic surfaces in Langstone Harbour, south coast of England. Blue-green algae investigated included species of Calothrix, Dermocarpa, Plectonema, Phormidium and Xenococcus. The blue-green algae are rapid colonisers and can make an important contribution to the pioneering communities on both toxic and non-toxic surfaces. A characteristic feature of the colonization process is the production of variable quantities of extracellular polymeric substances (EPS) which appear to function as adhesives. Cytochemical staining revealed the EPS to be an acidic polysaccharide and, therefore, chemically similar to the EPS produced by sessile diatoms. It is suggested that the EPS additionally assists in cell motility, acts as an antidesiccant and may influence the fouling process by combining with antifouling paint toxins and modifying the surface energy of substrata.     

Inhibition of fouling by marine bacteria immobilised in kappa-carrageenan beads

Antifouling solutions that leave little or no impact in the world's oceans are constantly being sought. This study employed the immobilisation of the antifouling bacterium Pseudoalteromonas tunicata in kappa-carrageenan to demonstrate how a surface may be protected from fouling by bacteria, i.e. a 'living paint'. Attempts so far to produce a 'living paint' have been limited in both longevity of effectiveness and demonstration of applicability, most noticeably regarding the lack of any field data. Here survival of bacteria immobilised in kappa-carrageenan for 12 months in the laboratory is demonstrated and evidence presented for inhibition of fouling for up to 7 weeks in the field (Sydney Harbour, NSW, Australia).     

Gill potentials in marine teleosts

Summary The transepithelial potentials of a wide variety of species of marine fishes have been measured. Most lie within the range 20–24 mV positive indicating that chloride is actively excreted while sodium is close to passive equilibrium. In most species the permeability to potassium is greater than that to sodium. In marked contrast to most other families, members of the Syngnathidae showed low or negative potentials. ²²Na flux measurements in Syngnathus acus showed a rate of flux comparable to that in other marine teleosts, indicating that sodium as well as chloride ions must be actively extruded in this species.     

Effect of substratum surface chemistry and surface energy on attachment of marine bacteria and algal spores

Two series of self-assembled monolayers (SAMs) of omega-substituted alkanethiolates on gold were used to systematically examine the effects of varying substratum surface chemistry and energy on the attachment of two model organisms of interest to the study of marine biofouling, the bacterium Cobetia marina (formerly Halomonas marina) and zoospores of the alga Ulva linza (formerly Enteromorpha linza). SAMs were formed on gold-coated glass slides from solutions containing mixtures of methyl- and carboxylic acid-terminated alkanethiols and mixtures of methyl- and hydroxyl-terminated alkanethiols. C. marina attached in increasing numbers to SAMs with decreasing advancing water contact angles (theta(AW)), in accordance with equation-of-state models of colloidal attachment. Previous studies of Ulva zoospore attachment to a series of mixed methyl- and hydroxyl-terminated SAMs showed a similar correlation between substratum theta(AW) and zoospore attachment. When the hydrophilic component of the SAMs was changed to carboxylate, however, the profile of attachment of Ulva was significantly different, suggesting that a more complex model of interfacial energetics is required.     

Chemical characterization of exopolysaccharides from the marine fouling diatom amphora coffeaeformis

Amphora coffeaeformis cells were grown in batch cultures under continuous illumination at 18°C for 10 d. Algal cells were removed by centrifugation, lyophilized and used for the extraction of exopolysaccharides using either 0.05 M EDTA, 1 M NaOH or 1.5 M NaCl. The 1.5 M NaCl treatment removed most exopolysaccharides. Glucose (81%) was the most abundant monosaccharide in the exopolysaccharides. The chemical composition data suggest that the exopolymers were acidic sulphated polysaccharides containing high concentrations of pyruvate (22%) and uronic acids (18%). These polysaccharides may play an important role in metal complexation and protection from desiccation in A. coffeaeformis.     

The origin of slow potentials on the tongue surface induced by frog glossopharyngeal efferent fiber stimulation

When the glossopharyngeal (GP) nerve of the frog was stimulated electrically, electropositive slow potentials were recorded from the tongue surface and depolarizing slow potentials from taste cells in the fungiform papillae. The amplitude of the slow potentials was stimulus strength- and the frequency-dependent. Generation of the slow potentials was not related to antidromic activity of myelinated afferent fibers in the GP nerve, but to orthodromic activity of autonomic post-ganglionic C fibers in the GP nerve. Intravenous injection of atropine abolished the positive and depolarizing slow potentials evoked by GP nerve stimulation, suggesting that the slow potentials were induced by the activity of parasympathetic post-ganglionic fibers. The amplitude and polarity of the slow potentials depended on the concentration of adapting NaCl solutions applied to the tongue surface. These results suggest that the slow potentials recorded from the tongue surface and taste cells are due to the liquid junction potential generated between saliva secreted from the lingual glands by GP nerve stimulation and the adapting solution on the tongue surface.     

Interspecific variation in patterns of adhesion of marine fouling to silicone surfaces

The adhesion of six fouling organisms: the barnacle Balanus eburneus, the gastropod mollusc Crepidulafornicata, the bivalve molluscs Crassostrea virginica and Ostrea/Dendrostrea spp., and the serpulid tubeworms Hydroides dianthus and H. elegans, to 12 silicone fouling-release surfaces was examined. Removal stress (adhesion strength) varied among the fouling species and among the surfaces. Principal component analysis of the removal stress data revealed that the fouling species fell into two distinct groups, one comprising the bivalve molluscs and tubeworms, and the other the barnacle and the gastropod mollusc. None of the silicone materials generated a minimum in removal stress for all the organisms tested, although several surfaces produced low adhesion strengths for both groups of species. These results suggest that fouling-release materials do not rank (in terms of adhesion strength) identically for all fouling organisms, and thus development of a globally-effective hull coating will continue to require testing against a diversity of encrusting species.     

Effects of temporal variability of disturbance on the succession in marine fouling communities in northern-central Chile

We investigated the effects of temporal variability in a disturbance regime on fouling communities at two study sites in a northern-central Chilean bay. Fouling assemblages grown on artificial settlement substrata were disturbed by mechanical removal of biomass at different time intervals. Using one single disturbance frequency (10 disturbance events over 5 months) we applied 7 different temporal disturbance treatments: a constant disturbance regime (identical intervals between disturbance events), and 6 variable treatments where both variableness and sequences of intervals between disturbance events were manipulated. Two levels of temporal variableness (low and high, i.e. disturbance events were either dispersed or highly clumped in time) in the disturbance regime were applied by modifying the time intervals between subsequent disturbance events. To investigate the temporal coupling between disturbance events and other ecological processes (e.g. larval supply and recruitment intensity), three different sequences of disturbance intervals were nested in each of the two levels of temporal variableness. Species richness, evenness, total abundance, and structure of communities that experienced the various disturbance regimes were compared at the end of the experiment (15 days after the last disturbance event). Disturbance strongly influenced the community structure and led to a decrease in evenness and total abundance but not species richness. In undisturbed reference communities, the dominant competitor Pyura chilensis (Tunicata) occupied most available space while this species was suppressed in all disturbed treatments. Surprisingly, neither temporal variableness in the disturbance regime nor the sequence of intervals between disturbance events had an effect on community structure. Temporal variability in high disturbance regimes may be of minor importance for fouling communities, because they are dominated by opportunistic species that are adapted to rapidly exploit available space.     

Current and emerging environmentally-friendly systems for fouling control in the marine environment

Following the ban in 2003 on the use of tributyl-tin compounds in antifouling coatings, the search for an environmentally-friendly alternative has accelerated. Biocidal TBT alternatives, such as diuron and Irgarol 1051®,¹ have proved to be environmentally damaging to marine organisms. The issue regarding the use of biocides is that concerning the half-life of the compounds which allow a perpetuation of the toxic effects into the marine food chain, and initiate changes in the early stages of the organisms' life-cycle. In addition, the break-down of biocides can result in metabolites with greater toxicity and longevity than the parent compound.     

Sediment challenge to promising ultra-low fouling hydrophilic surfaces in the marine environment

Hydrophilic coatings exhibit ultra-low fouling properties in numerous laboratory experiments. In stark contrast, the antifouling effect of such coatings in vitro failed when performing field tests in the marine environment. The fouling release performance of nonionic and zwitterionic hydrophilic polymers was substantially reduced compared to the controlled laboratory environment. Microscopy and spectroscopy revealed that a large proportion of the accumulated material in field tests contains inorganic compounds and diatomaceous soil. Diatoms adhered to the accumulated material on the coating, but not to the pristine polymer. Simulating field tests in the laboratory using sediment samples collected from the test sites showed that incorporated sand and diatomaceous earth impairs the fouling release characteristics of the coatings. When exposed to marine sediment from multiple locations, particulate matter accumulated on these coatings and served as attachment points for diatom adhesion and enhanced fouling. Future developments of hydrophilic coatings should consider accumulated sediment and its potential impact on the antifouling performance.     

Butenolide inhibits marine fouling by altering the primary metabolism of three target organisms

Butenolide is a very promising antifouling compound that inhibits ship hull fouling by a variety of marine organisms, but its antifouling mechanism was previously unknown. Here we report the first study of butenolide's molecular targets in three representative fouling organisms. In the barnacle Balanus (=Amphibalanus) amphitrite, butenolide bound to acetyl-CoA acetyltransferase 1 (ACAT1), which is involved in ketone body metabolism. Both the substrate and the product of ACAT1 increased larval settlement under butenolide treatment, suggesting its functional involvement. In the bryozoan Bugula neritina, butenolide bound to very long chain acyl-CoA dehydrogenase (ACADVL), actin, and glutathione S-transferases (GSTs). ACADVL is the first enzyme in the very long chain fatty acid β-oxidation pathway. The inhibition of this primary pathway for energy production in larvae by butenolide was supported by the finding that alternative energy sources (acetoacetate and pyruvate) increased larval attachment under butenolide treatment. In marine bacterium Vibrio sp. UST020129-010, butenolide bound to succinyl-CoA synthetase β subunit (SCSβ) and inhibited bacterial growth. ACAT1, ACADVL, and SCSβ are all involved in primary metabolism for energy production. These findings suggest that butenolide inhibits fouling by influencing the primary metabolism of target organisms.     

Settlement patterns of species in a marine fouling community and some mechanisms of succession

The succession of fouling organisms that settled on asbestos plates immersed at Garden Island. Western Australia, was partially caused by the settlement patterns of the species involved. Both temporal variations in the abundance and continuity of settlement of each species and the age of the communities in which each species settled abundantly contributed to producing the succession. Additionally, temporal variations in the settlement of each species probably resulted in variability in the pattern of succession.Balanus and Spirorbis, the two earliest species in the succession, settled continuously and abundantly so that they immediately occupied a substantial area. The species which predominated later in the succession, Anomia, Ostrea, encrusting bryozoans, and Mytilus, settled discontinuously so that they were unlikely to settle immediately on a newly immersed surface. Additionally, Anomia, Ostrea, and the encrusting bryozoans did not settle abundantly and did not occupy a substantial area while small. Thus, there was also a delay between the time when these species settled and the time when they had grown sufficiently large to occupy a substantial area.Mytilus was the only species that settled abundantly in established communities and thus could persist indefinitely in a community. Settlement of the other species which occurred earlier in the succession was largely restricted to newly immersed plates and consequently these species were limited in their duration in the succession by the life-spans of the individual organisms.     

Biodiversity characterisation and hydrodynamic consequences of marine fouling communities on marine renewable energy infrastructure in the Orkney Islands Archipelago,Scotland, UK

As part of ongoing commitments to produce electricity from renewable energy sources in Scotland, Orkney waters have been targeted for potential large-scale deployment of wave and tidal energy converting devices. Orkney has a well-developed infrastructure supporting the marine energy industry; recently enhanced by the construction of additional piers. A major concern to marine industries is biofouling on submerged structures, including energy converters and measurement instrumentation. In this study, the marine energy infrastructure and instrumentation were surveyed to characterise the biofouling. Fouling communities varied between deployment habitats; key species were identified allowing recommendations for scheduling device maintenance and preventing spread of invasive organisms. A method to measure the impact of biofouling on hydrodynamic response is described and applied to data from a wave-monitoring buoy deployed at a test site in Orkney. The results are discussed in relation to the accuracy of the measurement resources for power generation. Further applications are suggested for future testing in other scenarios, including tidal energy.     

Specificity of marine microbial surface interactions

The macromolecular surface components involved in intraspecific cell surface interactions of the green microalga Chlorella vulgaris and closely associated bacteria were investigated. The specific surface attachment between this alga and its associated bacteria is mediated by lectin-like macromolecules associated with the surfaces of these cells. The binding activity of these surface polymers was inhibited by specific simple sugars; this suggests the involvement of specific receptor-ligand binding sites on the interactive surfaces. Epifluorescent microscopic evaluation of bacteria-alga interactions in the presence and absence of the macromolecules that mediate these interactions showed that the glycoproteins active in these processes were specific to the microbial sources from which they were obtained. The demonstration and definition of the specificity of these interactions in mixed microbial populations may play an important role in our understanding of the dynamics of marine microbial populations in the sea.