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.     

Recent developments in superhydrophobic surfaces and their relevance to marine fouling: a review

In this review, a brief synopsis of superhydrophobicity (i.e. extreme non-wettability) and its implications on marine fouling are presented. A short overview of wettability and recent experimental developments aimed at fabricating superhydrophobic surfaces by tailoring their chemical nature and physical appearance (i.e. substratum texture) are reviewed. The formation of responsive/"smart" surfaces, which adjust their physico-chemical properties to variations in some outside physical stimulus, including light, temperature, electric field, or solvent, is also described. Finally, implications of tailoring the surface chemistry, texture, and responsiveness of surfaces on the design of effective marine fouling coatings are considered and discussed.     

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.     

Interspecific variation in life history relates to antipredator decisions by marine mesopredators on temperate reefs

As upper-level predatory fishes become overfished, mesopredators rise to become the new 'top' predators of over-exploited marine communities. To gain insight into ensuing mechanisms that might alter indirect species interactions, we examined how behavioural responses to an upper-level predatory fish might differ between mesopredator species with different life histories. In rocky reefs of the northeast Pacific Ocean, adult lingcod (Ophiodon elongatus) are upper-level predators that use a sit-and-wait hunting mode. Reef mesopredators that are prey to adult lingcod include kelp greenling (Hexagrammos decagrammus), younger lingcod, copper rockfish (Sebastes caurinus) and quillback rockfish (S. maliger). Across these mesopredators species, longevity and age at maturity increases and, consequently, the annual proportion of lifetime reproductive output decreases in the order just listed. Therefore, we hypothesized that the level of risk taken to acquire resources would vary interspecifically in that same order. During field experiments we manipulated predation risk with a model adult lingcod and used fixed video cameras to quantify interactions between mesopredators and tethered prey (Pandalus shrimps). We predicted that the probabilities of inspecting and attacking tethered prey would rank from highest to lowest and the timing of these behaviours would rank from earliest to latest as follows: kelp greenling, lingcod, copper rockfish, and quillback rockfish. We also predicted that responses to the model lingcod, such as avoidance of interactions with tethered prey, would rank from weakest to strongest in the same order. Results were consistent with our predictions suggesting that, despite occupying similar trophic levels, longer-lived mesopredators with late maturity have stronger antipredator responses and therefore experience lower foraging rates in the presence of predators than mesopredators with faster life histories. The corollary is that the fishery removal of top predators, which relaxes predation risk, could potentially lead to stronger increases in foraging rates for mesopredators with slower life histories.     

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.     

Site-specific variation in Antarctic marine biofilms established on artificial surfaces

The community structure and composition of marine microbial biofilms established on glass surfaces was investigated across three differentially contaminated Antarctic sites within McMurdo Sound. Diverse microbial communities were revealed at all sites using fluorescence in situ hybridization (FISH) and denaturing gradient gel electrophoresis (DGGE) techniques. Sequencing of excised DGGE bands demonstrated close affiliation with known psychrophiles or undescribed bacteria also recovered from the Antarctic environment. The majority of bacterial sequences were affiliated to the Gammaproteobacteria, Cytophaga/Flavobacteria of Bacteroidetes (CFB), Verrucomicrobia and Planctomycetales. Principal components analysis of quantitative FISH data revealed distinct differences in community composition between sites. Each of the sites were dominated by different bacterial groups: Alphaproteobacteria, Gammaproteobacteria and CFB at the least impacted site, Cape Armitage; green sulfur and sulfate reducing bacteria near the semi-impacted Scott Base and Planctomycetales and sulfate reducing bacteria near the highly impacted McMurdo Station. The highest abundance of archaea was detected near Scott Base (2.5% of total bacteria). Multivariate analyses (non-metric multidimensional scaling and analysis of similarities) of DGGE patterns revealed greater variability in community composition between sites than within sites. This is the first investigation of Antarctic biofilm structure and FISH results suggest that anthropogenic impacts may influence the complex composition of microbial communities.     

Interspecific interactions in the marine rotifer microcosm

Copepods and protozoans often co-exist in marinerotifer mass cultures. Interspecific interactionbetween the rotifer Brachionus rotundiformisTschugunoff and eight other zooplankton species,namely Brachionus plicatilis O. F. Müller (rotifer),Diaphanosoma celebensis Stingelin (cladoceran),Tigriopus japonicus Mori, Acartia sp. (copepod),Euplotes sp., Vorticella sp., an unidentifiedprotozoan species (P1 strain) (protozoan) and Artemiasp. (anostracan) at two developmental stages (nauplii –0.95 mm, 0 days old; adults – 3.3 mm, 19 days old) wereinvestigated in the laboratory.There was no contaminating species that contributedto an increase in rotifer population growth during theexperiments. Four types of interspecific interactionswere seen between B. rotundiformis and otherco-existing zooplankton species. These include effectson population growth: (1) both species declined, (2) onespecies is promoted while the other is not influenced,(3) one species is declined while the other is notinfluenced and (4) one species is promoted while theother declined. The first type was exhibited by B. rotundiformis vs B. plicatilis, B. rotundiformis vsD. celebensis and B. rotundiformis vs Artemia sp. The second type was exhibited by B. rotundiformis vsVorticella sp. and the third type by B. rotundiformisvs Euplotes sp. and B. rotundiformis vs T. japonicus. The fourth type was exhibited by B. rotundiformis vs Acartia sp. and B. rotundiformis vs P1 strain.     

Interspecific and temporal variation in herbivore responses to hybrid willows

We studied herbivory of two species of willows (Salix sericea and S. eriocephala) and their interspecific hybrids to test alternative hypotheses concerning the effects of hybridization on plant resistance. Individually marked plants were identified using morphological traits in the field and random amplified polymorphic DNA (RAPD) band analysis was used to verify the genetic status of many parental and hybrid plants. The desities of 12 herbivore species on plants in the field were compared between two parents and their F₂-type hybrids. We found about equal support for the additive, dominance, and hybrid susceptibility hypotheses over 4 years. In one year, one species supported the hybrid resistance hypothesis. Guild membership was not a good predictor of similar responses of species to hybrid versus parental plants. There were marked differences in support for particular hypotheses among years for four herbivore species. This study demonstrates the diversity of responses of phytophages in response to interspecific hybridization, and indicates that year-to-year variation in relative resistance of hybrid plants can be important.     

Photoreversible surfaces to regulate cell adhesion

We report the development of a photoreversible cell culture substrate. We demonstrate the capacity to modify the adhesivity of the substrate using light, altering its capacity to support cell growth. Polyelectrolyte multilayers (PEMs) were used to produce tunable substrates of different thickness and matrix stiffness, which have different intrinsic capacities to support cell adhesion and survival. Surfaces were top-coated with a poly(acrylic acid)-poly(allylamine hydrochloride) polyelectrolyte bilayer functionalized with a small fraction (<1%) of an azobenzene-based photoswitchable sidegroup, which included the cell-adhesive three-amino-acid peptide RGD. Irradiation with light-induced geometric switching of the azo bond, resulting in changes to RGD exposure and consequently to cell adhesion and survival, was investigated on a variety of surfaces of different thickness and stiffness. Substrate stiffness, as modified by the thickness, had a significant influence on the adhesion of NIH 3T3 cells, consistent with previous studies. However, by disrupting the isomerization state of the azobenzene-linked RGD and exposing it to the surface, cell adhesion and survival could be enhanced up to 40% when the positioning of the RGD peptide was manipulated on the softest substrates. These findings identify permissive, yet less-than-optimal, cell culture substrate conditions that can be substantially enhanced using noninvasive modification of the substrate triggered by light. Indeed, where cell adhesion was tuned to be suboptimal under baseline conditions, the light-induced triggers displayed the most enhanced effect, and identification of this 'Goldilocks zone' was key to enabling light triggering.     

Novel whole cell adhesion assays of three isolates of the fouling diatom Amphora coffeaeformis reveal diverse responses to surfaces of different wettability

Whole cell, strength of adhesion assays of three different isolates of the fouling diatom Amphora coffeaeformis were compared using a hydrophilic surface viz. acid washed glass (AWG), and a hydrophobic surface viz. a self assembled monolayer (SAM) of undecanethiol (UDT). Assays were performed using a newly designed turbulent flow channel that permits direct observation and recording of cell populations on a test surface. Exposure to continuous shear stress over 3?h revealed that the more motile isolate, WIL2, adhered much more strongly to both test surfaces compared to the other two strains. When the response of the isolates to shear stress after 3?h was compared, there was no significant difference in the percentage of cells removed, irrespective of surface wettability. Cells of the three isolates of A. coffeaeformis varied significantly in their response to different surfaces during initial adhesion, indicating the presence of a wide range of 'physiological races' within this species.     

Interspecific variation in growth of British pigeons Columbidae

Growth patterns of nestling Collared Doves Streptopetia decaocto , Woodpigeons Columba palumbus , Feral Pigeons C. livia and Stock Doves C. oenas , in Britain were compared. Open-nesting Collared Doves and Woodpigeons left the nest at about 60% of adult weight, hole-nesting Stock Doves at adult weight, and partial hole-nesting Feral Pigeons at an intermediate stage. Other species of pigeons and doves studied to date also fit this pattern. Stock Dove nestlings reared in nest-boxes reached heavier weights and left the nest later than those in more exposed sites. These results were correlated with differential predation pressure on open- versus hole-nesting birds.     

Adhesion and motility of fouling diatoms on a silicone elastomer

Recent demands for non-toxic antifouling technologies have led to increased interest in coatings based on silicone elastomers that 'release' macrofouling organisms when hydrodynamic conditions are sufficiently robust. However, these types of coatings accumulate diatom slimes, which are not released even from vessels operating at high speeds (>30 knots). In this study, adhesion strength and motility of three common fouling diatoms (Amphora coffeaeformis var. perpusilla (Grunow) Cleve, Craspedostauros australis Cox and Navicula perminuta Grunow) were measured on a poly-dimethylsiloxane elastomer (PDMSE) and acid-washed glass. Adhesion of the three species was stronger to PDMSE than to glass but the adhesion strengths varied. The wall shear stress required to remove 50% of cells from PDMSE was 17 Pa for Craspedostauros, 24 Pa for Amphora and >53 Pa for Navicula; the corresponding values for glass were 3, 10 and 25 Pa. In contrast, the motility of the three species showed little or no correlation between the two surfaces. Craspedostauros moved equally well on glass and PDMSE, Amphora moved more on glass initially before movement ceased and Navicula moved more on PDMSE before movement ceased. The results show that fouling diatoms adhere more strongly to a hydrophobic PDMSE surface, and this feature may contribute to their successful colonization of low surface energy, foul-release coatings. The results also indicate that diatom motility is not related to adhesion strength, and motility does not appear to be a useful indicator of surface preference by diatoms.     

Interspecific variation in resistance of two host tree species to spruce budworm

Woody plants regularly sustain biomass losses to herbivorous insects. Consequently, they have developed various resistance mechanisms to cope with insect attack. However, these mechanisms of defense and how they are affected by resource availability are not well understood. The present study aimed at evaluating and comparing the natural resistance (antibiosis and tolerance) of balsam fir (Abies balsamea [L.] Mill.) and white spruce (Picea glauca [Moench) Voss] to spruce budworm, Choristoneura fumiferana (Clem.), and how drainage site quality as a component of resource availability affects the expression of resistance over time (6 years). Our results showed that there are differences in natural resistance between the two tree species to spruce budworm, but it was not significantly affected by drainage quality. Balsam fir exhibited higher foliar toxic secondary compounds concentrations than white spruce in all drainage classes, resulting in lower male pupal mass, survival and longer male developmental time. This, however, did not prevent spruce budworm from consuming more foliage in balsam fir than in white spruce. This response suggests that either natural levels of measured secondary compounds do not provide sufficient toxicity to reduce defoliation, or spruce budworm has developed compensatory mechanisms, which allow it to utilize food resources more efficiently or minimize the toxic effects that are produced by its host's defensive compounds. Larvae exhibited lower pupal mass and higher mortality in rapidly drained and subhygric sites. Drainage class also affected the amount of foliage destroyed but its impact varied over the years and was probably influenced by climatic variables. These results demonstrate the complexity of predicting the effect of resource availability on tree defenses, especially when other confounding environmental factors can affect tree resource allocation and utilization.     

Effects of DNP on the cell surface properties of marine bacteria and its implication for adhesion to surfaces

The effect of 2, 4-dinitrophenol (DNP) on the extracelluar polysaccharides (EPS), cell surface charge, and the hydrophobicity of six marine bacterial cultures was studied, and its influence on attachment of these bacteria to glass and polystyrene was evaluated. DNP treatment did not influence cell surface charge and EPS production, but had a significant effect on hydrophobicity of both hydrophilic (p = 0.05) and hydrophobic (p = 0.01) cultures. Significant reduction in the attachment of all the six cultures to glass (p = 0.02) and polystyrene (p = 0.03) was observed after DNP treatment. Moreover, hydrophobicity but not the cell surface charge or EPS production influenced bacterial cell attachment to glass and polystyrene. From this study, it was evident that DNP treatment influenced bacterial cell surface hydrophobicity, which in turn, reduced bacterial adhesion to surfaces.     

Interspecific variation in metamorphic competence in marine invertebrates: the significance for comparative investigations into the timing of metamorphosis

Metamorphosis in marine invertebrate larvae is a dynamic, environmentallydependent process that integrates ontogeny with habitat selection.The capacity of many marine invertebrate larvae to survive andmaintain metamorphic competence in the absence of environmentalcues has been hypothesized to be an adaptive convergence (Hadfieldand others 2001). A survey of the literature reveals that asingle generalized hypothesis about metamorphic competence asan adaptive convergence is not sufficient to account for interspecificvariation in this character. In an attempt to capture this variation,we discuss the "desperate larva hypothesis" and propose twoadditional hypotheses called the "variable retention hypothesis"and the "death before dishonor hypothesis." To validate theseadditional hypotheses we collected data on taxa from the publishedliterature and performed a contingency analysis to detect correlationsbetween spontaneous metamorphosis, habitat specificity and/orlarval life-history mode, three characters relevant to environmentallyinduced settlement and metamorphosis. In order to account forphylogenetic bias in these correlations, we also constructeda phylogeny of these taxa and again performed a character-correlationanalysis. Both these tests suggest that juvenile habitat specificityis correlated to the capacity of individuals to retain the competentlarval state in the absence of substrate cues and thereforevalidate the existence of more than one hypothesis about metamorphiccompetence. We provide new data from the sea urchin Lytechinuspictus that suggest that nitric oxide (NO) and thyroxine hormonesignaling interact to determine the probability of settlementin response to a settlement cue. Similarly, we provide evidencethat thyroxine signaling in the sand dollar Dendraster excentricusincreases spontaneous metamorphosis in the absence of cues fromadult conspecifics in a manner that is independent of larvalage.     

Interspecific variation in sapling mortality in relation to growth and soil moisture

To examine the causes of landscape variation in forest community composition, we have quantified sapling mortality as a function of growth and soil moisture for seven dominant species in transition oak-northern hardwood forests of the northeastern USA. We located saplings in sites that encompassed a wide range of variation in soil moisture and light availability. In mesic conditions, the probability of mortality decays rapidly with increasing growth among shade tolerant species and more gradually among shade intolerant species: the rank order of survivorship at low growth rates is Tsuga canadensis > Fagus grandifolia > Acer saccharum > Fraxinus americana > Acer rubrum > Quercus rubra > Pinus strobus . The relationship between probability of mortality and growth does not vary with soil moisture among species insensitive to drought: Tsuga canadensis , Quercus rubra, and Pinus strobus . However, probability of mortality increases substantially with decreasing soil water availability for the other four species. Acer saccharum and Fagus grandifolia have high mortality rates under xeric conditions even when their growth is not suppressed. Acer rubrum and Fraxinus americana exhibited a steady but more gradual increase in the probability of mortality with decreasing soil moisture. Among the five deciduous hardwood species we examined there is a weak inverse relationship between the ability to survive growth suppression, a measure of shade tolerance, and the ability to survive in xeric conditions, a measure of drought tolerance. Tsuga canadensis , however, is tolerant of growth suppression and exhibits high survivorship in xeric conditions, while Pinus strobus is intolerant of growth suppression but insensitive to soil moisture. Species differences in water-dependent mortality are consistent with the species distributions across landscape gradients of soil water availability.     

Interspecific facilitation in a guild of benthic marine herbivores

Summary Interspecific relationships and trophic function within the urchin guild are considered in light of experiments and observations performed in situ. Two conclusions are reached: 1) interactions between members of the guild contribute to its persistence, and 2) the plant-herbivore interactions so important in structuring this community can best be evaluated when guild members are treated as a unit. As with other mixed species trophic units, the mechanisms of interspecies facilitation operate to reduce the effects of predation and increase foraging efficiency.     

Intraspecific variation in movement patterns: modeling individual behaviour in a large marine predator

In large marine predators, foraging entails movement. Quantitative models reveal how behaviours can mediate individual movement, such that deviations from a random pattern may reveal specific search tactics or behaviour. Using locations for 52 grey seals fitted with satellite-linked recorders on Sable Island; we modeled movement as a correlated random walk (CRW) for individual animals, at two temporal scales. Mean move length, turning angle, and net squared displacement (R²_n: the rate of change in area over time) at successive moves over 3 to 10 months were calculated. The distribution of move lengths of individual animals was compared to a Lévy distribution to determine if grey seals use a Lévy flight search tactic. Grey seals exhibited three types of movement as determined by CRW model fit: directed movers – animals displaying directed long distance travel that were significantly underpredicted by the CRW (23% of animals); residents – animals remaining in the area surrounding Sable Island that were overpredicted by the model (29% of animals); and correlated random walkers – those (48% of animals) in which movement was predicted by the CRW model. Kernel home range size differed significantly among all three movement types, as did travel speed, mean move length, mean R²_n and total distance traveled. Sex and season of deployment were significant predictors of movement type, with directed movers more likely to be male and residents more likely to be female. Only 30% of grey seals fit a Lévy distribution, which suggests that food patches used by the majority of seals are not randomly distributed. Intraspecific variation in movement behaviour is an important characteristic in grey seal foraging ecology, underscoring the need to account for such variability in developing models of habitat use and predation.