Barnacle Balanus Improvisus Research Articles

LINKING LARVAL SUPPLY TO RECRUITMENT: FLOW-MEDIATED CONTROL OF INITIAL ADHESION OF BARNACLE LARVAE

Dispersal of propagules may have far-reaching consequences for the local dynamics of open populations. In aquatic environments the dispersal and supply of larvae is strongly influenced by coastal-scale hydrodynamics. The role of local flow on settlement and recruitment is, however, poorly understood. In a test of the effect of local hydrodynamics on recruitment dynamics we studied the relationships between local flow speed and larval supply, contact rate, settlement, and recruitment rates for the barnacle Balanus improvisus. Planktonic cyprid larvae were sampled with pumps while suspended panels were used to measure initial contact (grease-coated panels), settlement (5-d immersion), and recruitment (30-d immersion). Larval supply varied with coastal-scale upwelling but was uncorrelated to local flow speed. Settlement rate was highly correlated to contact rate, and the proportion of settling larvae increased with established recruit density. In contrast to model predictions, contact rate was negatively correlated with local flow speed, which explained 33% of total variation. This correlation was maintained through settlement and recruitment suggesting that flow-mediated initial contact is an important link between larval supply and recruitment. No evidence from field studies indicated behavioral responses by larvae to flow although observations in a laboratory flume suggested active rejection of potential settlement sites at increasing flow speeds. It is suggested that initial adhesion is limited by flow speed through drag and lift forces acting on larvae. A conceptual model of mechanisms controlling the transfer of planktonic larvae to recruited benthic individuals is proposed.

Reversible antifouling effect of the cyclotide cycloviolacin O2 against barnacles.

Cycloviolacin O2, a plant peptide of the cyclotide family, is shown to have potent effects against fouling barnacles (Balanus improvisus), with complete inhibition of settlement at a concentration of 0.25 microM. The effect of cycloviolacin O2 against barnacles is reversible and nontoxic in the bioassay employed in these studies. Cycloviolacin O2 was isolated from the terrestrial plant Viola odorata by strong cation exchange and reversed-phase HPLC and identified by mass spectrometry following aminoethylation and enzymatic cleavage.

Isolated and combined impacts of blue mussels ( Mytilus edulis) and barnacles ( Balanus improvisus) on structure and diversity of a fouling community

Effects of two presumably dominant competitors, the blue mussel Mytilus edulis and the barnacle Balanus improvisus on recruitment, population dynamics and community structure on hard substrata were experimentally investigated in the subtidal Kiel Fjord, Western Baltic. The hypothesis that blue mussels and/or barnacles are local dominants and strongly influence succession and community structure was tested by monitoring succession in the presence and absence of simulated predation on either or both species. Manipulations included blue mussel removal, barnacle removal, combined blue mussel and barnacle removal, as well as a control treatment for natural (non-manipulated) succession. In the second part of the experiment, recovery from the treatments was monitored over 1 year. During the manipulative phase of the experiment, blue mussels had a negative effect on recruitment of species, whereas barnacles had no significant effect. Even so, a negative synergistic effect of blue mussels and barnacles was detected. Calculation of species richness and diversity H′ (Shannon Index) showed a negative synergistic effect of blue mussels and barnacles on community structure. Additionally, diversity H′ was negatively affected by the dominant competitor M. edulis. These effects were also detectable in the ANOSIM-Analysis. The non-manipulative phase of the experiment brought about a drastic loss of diversity and species richness. Blue mussels dominated all four communities. Barnacles were the only other species still being able to coexist with mussels. Effects of simulated predation disappeared fast. Thus, in the absence of predation on blue mussels, M. edulis within a few months dominates available space, and diversity of the benthic community is low. In contrast, when mussel dominance is controlled by specific predators, more species may persist and diversity remains high.

Surface wettability as a determinant in the settlement of the barnacle Balanus Improvisus (DARWIN)

Several studies have shown that the initial surface wettability, is of importance in the settlement of macrofouling larvae such as barnacles, bryozoans and hydroids in the field as well as in laboratory assays. In this study we present results from laboratory assays using hydrophilic and hydrophobic polystyrene (PS) and cyprid larvae of Balanus improvisus (Darwin). The results obtained differ markedly from those reported for the barnacle Balanus amphitrite (Darwin), where a high surface wettability seemed to be preferred for settlement. Our results show that a surface with intermediary wettability (hydrophilic PS) reduced settlement by 38% as compared to surfaces of low wettability (hydrophobic PS) during an 8-day period. During the experiment, the wettability in the hydrophilic PS dishes was not significantly changed as measured by advancing contact angle with mQ water. Over an 8-day period wettability of the hydrophobic PS dishes approached that of the hydrophilic PS surfaces. We further conducted experiments with highly hydrophilic and highly hydrophobic methylsilane-treated glass surfaces with known chemistry. In this experiment, the settlement of cyprid larvae was completely inhibited by the high wettability surfaces. Contact angle measurements revealed that the wettability during the length of the experiment of the hydrophilic glass surfaces was not significantly altered. We conclude by these experiments that even an intermediate wettability can significantly affect the overall settlement success of the barnacle B. improvisus. The mechanism by which the settlement is impeded might be biologically mediated through the recognition by cyprid larvae of the molecular composition of the surface when the cyprid reverts to the settlement phase, i.e. when swimming behaviour is abandoned in favour of surface exploration, or it is mediated by physicochemical forces acting between the surface and the larval body or the larval antennules.

Antifouling activity of brominated cyclopeptides from the marine sponge Geodia barretti.

In this work, we show the potent antifouling effects of two compounds, barettin (cyclo[(6-bromo-8-entryptophan)arginine]) (1), isolated as a Z/E mixture (87/13), and 8,9-dihydrobarettin (cyclo[(6-bromotryptophan)arginine]) (2), isolated from the marine sponge Geodia barretti. The compounds were isolated guided by their ability to inhibit the settlement of cyprid larvae of the barnacle Balanusimprovisus, and their structures were determined by means of mass spectrometry, NMR, and quantitative amino acid analysis. The activities of these brominated diketopiperazine-like cyclic dipeptides are in the range of antifouling agents in use today, as shown by their EC(50) values of 0.9 and 7.9 microM, respectively. However, contrary to today's antifouling agents, the effects of barettin and 8,9-dihydrobarettin are nontoxic and reversible. A small set of synthetic analogues, including l-arginine, l-tryptophan, 5-bromo-d,l-tryptophan, 6-bromo-d,l-tryptophan, and 6-fluoro-d,l-tryptophan, were tested for possible structure-activity relationships. None of these compounds showed any effect at a concentration of 10 microM. We hypothesize that the isolated compounds are part of the sponge's chemical defense to deter fouling organisms. This theory is supported by the fact that barettin is found in water exposed to living specimens of G. barretti in concentrations that completely inhibit barnacles from settling.

Rejection of unsuitable substrata as a potential driver of aggregated settlement in the barnacle Balanus improvisus

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 275:199-210 (2004) - doi:10.3354/meps275199 Rejection of unsuitable substrata as a potential driver of aggregated settlement in the barnacle Balanus improvisus K. M. Berntsson1,*, P. R. Jonsson1, A. I. Larsson1, S. Holdt2 1Tjärnö Marine Biological Laboratory, Department of Marine Ecology, Göteborg University, 452 96 Strömstad, Sweden 2Zoological Institute, University of Copenhagen, 2100 Copenhagen, Denmark *Email: kent.berntsson@tmbl.gu.se ABSTRACT: Many marine invertebrate larvae have the capacity to reject or accept settlement sites based on a broad range of cues. Species-specific settlement responses to different cues are often inferred from final settlement choice in the field. Little is known about species-specific larval behaviour in response to different cues and, in particular, how the behaviour is linked to final settlement. Rejection of unsuitable substrata may be an important driving force that leads to aggregated settlement patterns. This study examines rejection responses in relation to surface attractiveness for settlement under field and laboratory conditions in the barnacle Balanus improvisus. The attractiveness for settlement was manipulated by varying surface texture in combination with crude extract from conspecific adults. Active rejection behaviour was examined as a function of surface texture and conspecific pheromones in the field and then related to behavioural responses under static and flowing conditions in the laboratory. Recruitment was heavily reduced on substrata with ribbed microtexture compared to smooth substrata and unaffected by crude extract from conspecific adults. On average, 28% of the cyprids that encountered smooth settlement panels recruited. The proportion of cyprids recruiting on 2 microtextured substrata after encounter was 5 and 1% respectively. In behavioural experiments cyprids showed higher motion speed and dispersal rate on textured substrata, which indicated less exploratory behaviour than on smooth substrata, while an addition of conspecific extract increased intensities of surface exploration on all types of substrata. Flume experiments further demonstrated that cyprids are more prone to leave textured substrata and that the rejection rate was independent of conspecific extract. This work emphasises the role of larval behaviour as a potentially powerful mechanism determining final recruitment pattern. It is concluded that the choice of settlement site is an important factor in the settlement process of B. improvisus, and the results suggest that surface topography may be a stronger cue for settlement than chemical attraction by conspecific adults in this species. This study presents an example whereby rejection of unsuitable substrata leads to an increased larval pool on adjacent substrata that are suitable for settlement, and indicates that this process may drive aggregated settlement in the barnacle B. improvisus. KEY WORDS: Balanus improvisus · Barnacle · Cyprid · Larval behaviour · Settlement · Recruitment · Surface texture · Larval ecology Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 275. Online publication date: July 14, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.

Chemical settlement inhibition versus post-settlement mortality as an explanation for differential fouling of two congeneric seaweeds.

It has been proposed that seaweed secondary metabolites, e.g. brown algal phlorotannins, may have an ecologically important function as a chemical defence against epiphytes, by acting against colonisation of epiphytic organisms. We tested whether the low epiphytic abundance on the invasive brown seaweed Fucus evanescens, compared to the congeneric F. vesiculosus, is due to a more effective chemical defence against epiphyte colonisation. A field survey of the distribution of the common fouling organism Balanus improvisus (Cirripedia) showed that the abundance was consistently lower on F. evanescens than on F. vesiculosus. However, contrary to expectations, results from experimental studies indicated that F. vesiculosus has a more effective anti-settlement defence than F. evanescens. In settlement experiments with intact fronds of the two Fucus species, both species deterred settlement by barnacle larvae, but settlement was lower on F. vesiculosus both in choice and no-choice experiments. Phlorotannins from F. vesiculosus also had a stronger negative effect on larval settlement and were active at a lower concentration than those from F. evanescens. The results show that Fucus phlorotannins have the potential to inhibit settlement of invertebrate larvae, but that settlement inhibition cannot explain the lower abundance of the barnacle Balanus improvisus on F. evanescens compared to F. vesiculosus. Assessment of barnacle survival in the laboratory and in the field showed that this pattern could instead be attributed to a higher mortality of newly settled barnacles. Observation suggests that the increased mortality was due to detachment of young barnacles from the seaweed surface. This shows that the antifouling mechanism of F. evanescens acts on post-settlement stages of B. improvisus.

Geographical and seasonal variation of trace metal bioavailabilities in the Gulf of Gdansk, Baltic Sea using mussels ( Mytilus trossulus ) and barnacles ( Balanus improvisus ) as biomonitors

The barnacle Balanus improvisus and the mussel Mytilus trossulus have been used as biomonitors of the trace metals Cu, Zn, Cd, Fe, Pb, Mn and Ni at five sublittoral sites in the Gulf of Gdansk (Baltic Sea) between February 2000 and September 2001. The study has established a benchmark against which future biomonitoring programmes will be able to establish changes in local metal pollution, particularly if metal loadings in the river Vistula (draining into the Gulf) alter in the future. The study highlighted differences in trace metal bioavailabilities to both barnacles and mussels, geographically and over time. Accumulated metal concentrations of Cu, Zn, Fe, Pb and Ni, but not Cd or Mn, were correlated in the barnacles and mussels, suggesting that the bioavailabilities of the former metals to the two biomonitors were similar. The barnacles showed greater discriminatory power than the mussels as trace metal biomonitors. Concentrations of trace metals in surficial sediments (<63 μm) did not correlate significantly with accumulated metal concentrations in either barnacles or mussels, indicating that sediment metal concentrations are not necessarily good proxy measures of ambient trace metal bioavailabilities to the local coastal filter feeders.

Inhibitory effects of red algal extracts on larval settlement of the barnacle Balanus improvisus

We examined the chemical antifouling properties of four sublittoral red algae, Chondrus crispus, Delesseria sanguinea, Osmundea ramosissima, and Polyides rotundus, which are all rarely fouled in the field. Two different approaches were used. Firstly, we tested the effects of lipophilic crude extracts on the settlement behaviour of cyprid larvae of the co-existing barnacle Balanus improvisus. Secondly, in a settlement preference experiment, we tested whether B. improvisus cyprid larvae settle on living algae when given a choice between natural algal surfaces and control surfaces. With this procedure, we were able to test both if the algae inhibit recruitment of cyprids, and if this inhibition is a result of chemistry. The settlement of B. improvisus larvae was strongly inhibited at concentrations estimated to be potentially ecologically relevant for all of the tested extracts. However, only C. crispus significantly inhibited settlement in the preference experiment, even though there was also a tendency for settlement inhibition on P. rotundus and O. ramosissima. In contrast, D. sanguinea seemed to stimulate settlement. This contradiction probably resulted from an extraction of metabolites that naturally occur only inside the alga. However, as this study shows, a combination of settlement assays with whole-cell extracts and preference tests of ecologically relevant fouling organisms on natural algal and control surfaces may be a useful procedure to avoid erroneous conclusions regarding natural antifouling roles of compounds based on settlement assays with only whole-cell extracts. Furthermore, this study also shows that production of inhibitory metabolites may explain the low degree of fouling, especially by B. improvisus, on C. crispus.

Temporal and Spatial Patterns in Recruitment and Succession of a Temperate Marine Fouling Assemblage: a Comparison of Static Panels and Boat Hulls during the Boating Season

Protection against biofouling is essential for efficient operation of boats and ships. Restrictions on the use of traditional, toxic antifouling coatings call for new less toxic methods. Future antifouling strategies will likely be based on more specific action against dominant foulers and will require more detailed information about spatial and temporal differences in fouling communities on artificial substrates. In this study, the recruitment and succession of fouling organisms was examined on artificial (PMMA) panels exposed to natural flow speeds on the Skagerrak coast (Sweden). The recruitment of foulers on static panels was then compared to fouling allowed to develop on boat hulls in surveys of new non‐toxic coatings. The temporal and spatial variation in recruitment was examined on a monthly interval within the boating season, from May‐September. Furthermore, the succession of the fouling community was examined during the same interval. A total of 12 sessile inverte brate species was recorded on the static panels with dominant foulers being the barnacle Balanus improvisus (July‐September) and the mussel Mytilus edulis (June‐August). The mean abundance during peak settlement on panels after 1 month's deployment was 370±134 individuals dm‐2 for B. improvisus and 340±415 individuals dm‐2 for M. edulis. The succession of foulers on the panels led to a dominance of M. edulis (maximum of 7470±2830 individuals dm‐2) over B. improvisus (maximum of 2295±680 individuals dm‐2). This was in contrast to the fouling development on boat hulls, examined after 4 months exposure in 3 successive years, where B. improvisus was the dominant species (mean abundance 222±104 and maximum 713±527 indivi duals dm‐2). Some boats were covered to an extent of almost 100% by B. improvisus with only a few M. edulis (mean abundance 20±16). The biomass of fouling on boat hulls varied from average dry weights of 1.3±1 to 13±5 g dm‐2. These results show that extrapolation from static panels (common in evaluation of antifouling performance) to fouling on boat hulls may be proble matic.

Temporal and spatial patterns in recruitment and succession of a temperate marine fouling assemblage: A comparison of static panels and boat hulls during the boating season

Protection against biofouling is essential for efficient operation of boats and ships. Restrictions on the use of traditional, toxic antifouling coatings call for new less toxic methods. Future antifouling strategies will likely be based on more specific action against dominant foulers and will require more detailed information about spatial and temporal differences in fouling communities on artificial substrates. In this study, the recruitment and succession of fouling organisms was examined on artificial (PMMA) panels exposed to natural flow speeds on the Skagerrak coast (Sweden). The recruitment of foulers on static panels was then compared to fouling allowed to develop on boat hulls in surveys of new non‐toxic coatings. The temporal and spatial variation in recruitment was examined on a monthly interval within the boating season, from May‐September. Furthermore, the succession of the fouling community was examined during the same interval. A total of 12 sessile inverte brate species was recorded on the static panels with dominant foulers being the barnacle Balanus improvisus (July‐September) and the mussel Mytilus edulis (June‐August). The mean abundance during peak settlement on panels after 1 month's deployment was 370±134 individuals dm‐2 for B. improvisus and 340±415 individuals dm‐2 for M. edulis. The succession of foulers on the panels led to a dominance of M. edulis (maximum of 7470±2830 individuals dm‐2) over B. improvisus (maximum of 2295±680 individuals dm‐2). This was in contrast to the fouling development on boat hulls, examined after 4 months exposure in 3 successive years, where B. improvisus was the dominant species (mean abundance 222±104 and maximum 713±527 indivi duals dm‐2). Some boats were covered to an extent of almost 100% by B. improvisus with only a few M. edulis (mean abundance 20±16). The biomass of fouling on boat hulls varied from average dry weights of 1.3±1 to 13±5 g dm‐2. These results show that extrapolation from static panels (common in evaluation of antifouling performance) to fouling on boat hulls may be proble matic.

Biomonitoring of trace metal availabilities in the Thames estuary using a suite of littoral biomonitors

This study employed a suite of three biomonitors to investigate trace metal pollution in the Thames estuary, a region of significant clean-up of contaminants and the cumulative return of fauna and flora over the last two decades. The biomonitors chosen are the brown seaweed Fucus vesiculosus (bladder wrack), the barnacle Balanus improvisus and the talitrid amphipod crustacean Orchestia gammarellus, in order to obtain data on the bioavailabilities of Zn, Cu, Cd, Pb, Fe, Ag and Mn in the Thames estuary in 2001, as a basis for future comparisons as pollution is further reduced in the Thames. Accumulated metal concentrations in these organisms represent integrated records of the total bioavailabilities of the metals to that organism at that location over a previous time period, and comparisons of accumulated concentrations in a biomonitor between sites are indeed comparisons of the recent contaminant bioavailabilities to that biomonitor. All three biomonitors showed geographical differences in trace metal bioavailabilities along the Thames estuary. There was general agreement in the conclusions to be drawn from each of the three species used. Raised bioavailabilities of zinc, cadmium, lead, iron and manganese are present, particularly in the middle region of the Thames investigated, downstream of the effluent discharges of the sewage works at Beckton and Crossness.

Relative strengths of competition for space and food in a sessile filter feeder.

Previous workers have demonstrated that sessile filter feeders compete for food and space, but little is known about the relative strengths of these two processes. To determine this, the density and position of barnacles (Balanus improvisus) in a unidirectional current were manipulated to alter the amount of competition for space and food, respectively. Results indicated that competition for space significantly reduced growth, and marginally reduced survivorship. Competition for food was also detected, but only among uncrowded individuals; thus, it appears to be the weaker of the two interactions. However, under crowded conditions, downstream individuals actually grew more than those upstream. The most likely explanation for this result is that downstream individuals fed more efficiently because they were not exposed to the full force of the current. The results also suggest that since natural densities started high but continually decreased throughout the study, barnacles undergo an ontogenetic shift in the relative importance of these processes.

The Baltic—a sea of invaders

There are about 100 nonindigenous species recorded in the Baltic Sea. Invasive species have resulted in major changes in nearshore ecosystems, especially in coastal lagoons and inlets that can be identified as "centres of xenodiversity". Fewer than 70 of these species have established reproducing populations. Dominant invasion vectors include unintentional introductions via ballast water, tank sediments, and hull fouling, aquaculture, and the construction of canals that have facilitated active or passive natural dispersal. Of the approximately 60 unintentionally introduced species with a known invasion history, 38 are transoceanic (including 19 Atlantic species of American origin) and 18 of Ponto-Caspian origin. Species that have caused economic damage to fisheries, shipping, and industry include the hydrozoan Cordylophora caspia, the barnacle Balanus improvisus, the cladoceran Cercopagis pengoi, and the bivalve Dreissena polymorpha. The Baltic Sea has served as a secondary source of nonindigenous species to the North American Great Lakes. Further study is warranted to quantify large-scale ecosystem changes in the Baltic associated with establishment and population growth of nonindigenous species and to prevent future invasions.

Interactions between substratum rugosity, colonization density and periwinkle grazing efficiency

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 225:239-249 (2002) - doi:10.3354/meps225239 Interactions between substratum rugosity, colonization density and periwinkle grazing efficiency M. Wahl1,*, K. Hoppe2 1University of Namibia, Windhoek, Namibia 2Zoologisches Insitut, Universität Kiel, Olshausenstr. 40, 24098 Kiel, Germany *E-mail: mwahl@zoologie.uni-kiel.de ABSTRACT: Both surface texture and littorinid grazing are known to influence the establishment of many shallow-water benthic hard-bottom communities. However, the effects of these factors and their interactions have not yet been investigated in a quantifiable manner. This investigation aims to assess the interactive effect of both factors in a strictly standardized manner. Natural recruitment by diatoms, the barnacle Balanus improvisus and the tube-building polychaete Polydora sp. was monitored under a 2-factorial treatment: grazing by the periwinkle Littorina littorea (Factor 1; 2 levels: 1 or no snails per plate) on artificial recruitment plates of different initial surface rugosities (Factor 2; 5 levels: smooth, 0.1, 0.5, 1 and 5 mm rugosity elements). In the absence of grazers, barnacle recruitment decreased with increasing initial rugosity, polychaete recruitment peaked at intermediate rugosities, and diatoms exhibited contrasting recruitment patterns in an in vitro and an in situ experiment. When preferred recruitment sites coincided for Polydora and B. improvisus, a competition for space could be inferred from a negative correlation between the 2 species. However, when the overlap of requirements weakened on the 5 rugosities, the relationship was positive, but was not statistically significant. Grazing efficiency by L. littorea depended on initial rugosity, generally showing minimum values on intermediate rugosities which is attributable to a mismatch between radula dimensions and surface structures in these rugosity classes. Additionally, grazing effects tended to increase with higher prey densities. As all factors‹initial rugosity, grazing, colonizer species‹interact with each other, the outcome of recruitment under combined factors is difficult to predict from single factor effects. KEY WORDS: Grazing efficiency · Surface rugosity · Recruitment · Multiple interactions Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 225. Online publication date: January 11, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

The adhesion of the barnacle, Balanus improvisus, to poly(dimethylsiloxane) fouling-release coatings and poly(methyl methacrylate) panels: The effect of barnacle size on strength and failure mode

Measurements were made of the bond strength of cyprids and barnacles (Balanus improvisus) attached to poly(dimethylsiloxane) (PDMS) fouling-release coatings and poly(methyl methacrylate) (PMMA) panels as a function of barnacle base plate size (0.05-90 mm2). The vertical forces necessary to dislodge cyprids and newly metamorphosed barnacles (base plate < 0.5 mm2) were found to be equal for the two different substrates. This unexpected result was explained by the occurrence of cohesive failure in the cyprid/barnacle part. A significantly higher detachment force was observed for larger barnacles (base plate > 0.5 mm2) when dislodged from the PMMA compared to the PDMS. Analysis of the failure surfaces with light microscopy and scanning electron microscopy (SEM) showed a gradual transition in failure mode from a total cohesive within the barnacle to a mixed failure mode during barnacle growth. This transition, which is a measure of the balance between the cohesive strength of the barnacle base plate and the adhesion bond to the surface, occurs earlier or with smaller barnacles when detached from the PDMS. The quantification of the remaining fraction of the base plate at the polymeric failure surfaces appears to be a function of barnacle bioadhesive bond strength and is, therefore, suggested to be used as a new parameter for evaluating the release properties of new coatings formulations.

Surface active adrenoceptor compounds prevent the settlement of cyprid larvae of Balanus improvisus

The barnacle Balanus improvisus is the major fouling macroorganism in Swedish waters and it colonizes most man‐made surfaces submerged in the sea. New or impending legislation restricts the use of traditional, hazardous antifouling coatings based on heavy metals, mainly copper and tin. This calls for the development of new non‐toxic methods that prevent barnacle settlement. In this work several adrenoceptor compounds are shown to be very efficient in preventing the settlement of cyprid larvae of B. improvisus. The settlement rate of laboratory‐reared cyprids was studied in hydrophilised polystyrene dishes containing adrenoceptor antagonists and agonists dissolved in seawater. Two of these drugs, medetomidine and clonidine, repeatedly inhibited settlement at concentrations between 1 nM and 10 nM. In the vertebrate adrenoceptor classification system, which separates pharmacological substances according to their receptor affinity, both of these substances are classified as α2 adrenoceptor agonists. An inhibiting effect on presyn‐aptic receptors is suggested, but the localization of the receptor effect requires futher studies. Experiments also revealed that the inhibiting effect of medetomidine was reversible. Cyprids incubated with medetomidine for 20 h attached and metamorphosed into juvenile barnacles after washing and transferrence to seawater. The antagonizing compound atipamezole reversed the effect of medetomidine. This observation supports the assumption that this substance acts at the receptor level. Studies of the surface affinity of medetomidine revealed a strong tendency to accumulate in solid/ liquid phase boundaries. This ability makes it particularly attractive as a candidate for the development of a slow‐release carrier in marine coatings. Panels coated with medetomidine in an acrylate polymer and exposed in the field reduced the recruitment of B. improvisus by 96% after 4 weeks and by 70% after 8 weeks.

Mechanical aspects of silicone coatings for hard foulant control

Barnacle release mechanisms and the durability of silicone coatings have been studied. Release studies were performed on both transparent, single‐layer silicone coatings and duplex silicone coatings. The release forces of pseudobarnacles (epoxied studs) and Chesapeake Bay barnacles (Balanus improvisus) were measured with a pull‐off (tension) tester; modes of release were revealed in video recordings of the separation process from transparent coatings on glass. Scratch tests with 0.8 mm spherically‐tipped diamond provided a measure of durability (tear resistance). Release forces from both coatings decreased as coating thickness increased. Both pseudobarnacles and barnacles separated by a peeling process, although differences in peeling modes were seen. The durability of coatings increased with increasing coating thickness. Release behavior is discussed in terms of a fracture mechanic's model for pull‐off separation, and the differences in adhesion between barnacles and pseudobarnacles are described.

Reduction of barnacle recruitment on micro‐textured surfaces: Analysis of effective topographic characteristics and evaluation of skin friction

This study investigates five designed micro‐textured surfaces and their effects on barnacle fouling and hydrodynamic drag. Three of the micro‐textures were developed in the present study and evaluated together with two commercial riblet films. All micro‐structures were arranged as longitudinal grooves with different profile depths, widths and angles of inclination. In field tests the recruitment of the barnacle Balanus improvisus on micro‐textured surfaces and smooth controls was evaluated. All micro‐textured surfaces reduced recruitment, and the most efficient texture reduced recruitment by 98%. For some micro‐textures the reduction of recruitment declined as settlement intensity increased. In a correlative analysis, the trigonometric inclination of the micro‐structures explained most of the recruitment reduction. The steepest angle of inclination caused a massive reduction in barnacle settlement. Surface micro‐structures may affect the boundary‐layer flow and the hydrodynamic drag (skin friction) of the surface. The skin friction was empirically measured in a flow channel using a sub‐set of the tested micro‐textures. The measurements of skin friction showed that the orientation of the microstructures is important, with a minimum friction when the grooves are parallel to the flow. For one of the micro‐textures the skin friction was ca 10% lower compared to a hydraulically smooth surface. It is concluded that, depending on the flow speed, micro‐textures will not significantly increase skin friction when arranged parallel to the flow, even at moderate protrusion through the viscous sub‐layer.

Analysis of behavioural rejection of micro-textured surfaces and implications for recruitment by the barnacle Balanus improvisus

Experiments performed in the field and in the laboratory show that the barnacle, Balanus improvisus, preferentially settles on smooth surfaces. Settlement and recruitment of B. improvisus was evaluated on micro-textured surfaces with scales of surface texture ranging from 1 to 100 µm in profile heights. Surface texture with profile heights within a topographic range of 30-45 µm reduced settlement and recruitment by 92% as compared to smooth surfaces. The reduction in recruitment on micro-textured surfaces is best explained by behavioural responses to surface topography. Behavioural experiments show that cyprids have a higher propensity for smooth surfaces than for micro-textured surfaces. Cyprids spend more time exploring smooth surfaces and more time swimming when exposed to micro-textured surfaces. Micro-textured surfaces are more often rejected by cyprids after exploration than smooth surfaces. It is suggested that some scales of surface texture could be exploited to improve future anti-fouling techniques in geographical areas where Balanus improvisus is a severe fouling problem.