Cyprid Settlement Research Articles

Antifouling activity of meroditerpenoids from the marine brown alga Halidrys siliquosa.

Nine tetraprenyltoluquinol-related metabolites (1-9) have been isolated from the organic extract of the temperate brown alga Halidrys siliquosa that exhibits antifouling properties. The planar structure of compounds 1-9 was elucidated on the basis of extensive spectroscopic analysis and by comparison of the data with those of related metabolites. Antifouling and toxicity tests were conducted on these compounds: the most active (compounds 2, 6, and 9) inhibited both the growth of four strains of bacteria (MICs < 2.5 microg/mL) and settlement of cyprids of Balanus amphitrite (EC50 < 5 microg/mL), the latter at nontoxic concentrations (LC50 > 5 microg/mL).

Inhibition of barnacle (Amphibalanus amphitrite) cyprid settlement by means of localized, pulsed electric fields

The increasing needs for environmental friendly antifouling coatings have led to investigation of new alternatives for replacing copper and TBT-based paints. In this study, results are presented from larval settlement assays of the barnacle Amphibalanus (= Balanus) amphitrite on planar, interdigitated electrodes (IDE), having 8 or 25 μm of inter-electrode spacing, upon the application of pulsed electric fields (PEF). Using pulses of 100 ms in duration, 200 Hz in frequency and 10 V in pulse amplitude, barnacle settlement below 5% was observed, while similar IDE surfaces without pulse application had an average of 40% settlement. The spacing between the electrodes did not affect cyprid settlement. Assays with lower PEF amplitudes did not show significant settlement inhibition. On the basis of the settlement assays, the calculated minimum energy requirement to inhibit barnacle settlement is 2.8 W h m−2.

Settlement of the barnacle Balanus improvisus: The roles of dopamine and serotonin

The regulation of the settlement process in barnacles has attracted research interest due to their role as fouling organisms. The involvement of neurotransmitters in the regulation of settlement of marine invertebrate larvae has been described in several species. In this work, we reported the effects of the neurotransmitters dopamine and serotonin on the settlement of cyprids of the barnacle Balanus improvisus and described differences among cyprids of different ages. Also, we tested the effects of dopaminergic and serotonergic agonists and antagonists on settlement of cyprid larvae. We found that dopamine significantly stimulated settlement of 2‐ and 4‐day‐old cyprids, while serotonin exerted an inhibitory effect, regardless of cyprid age. The agonists and antagonists to the two neurotransmitters were not able to stimulate settlement but in general had either an inhibitory or no effect. We compared our results to those previously reported of the roles of dopamine and serotonin in the settlement of Balanus amphitrite. There appeared to be striking differences in the effects of these neurotransmitters between the two species because it has been reported that serotonin induces settlement in B. amphitrite and that dopamine inhibits it. This suggested that dopamine and serotonin play pivotal roles in settlement of barnacle but may act in different ways in the two species.

Species-specific engineered antifouling topographies: correlations between the settlement of algal zoospores and barnacle cyprids

Novel, non-toxic antifouling technologies are focused on the manipulation of surface topography to deter settlement of the dispersal stages of fouling organisms. This study investigated the effect of the aspect ratio (feature height/feature width) of topographical features engineered in polydimethylsiloxane, on the settlement of cyprids of Balanus amphitrite and zoospores of Ulva linza. The correlation of relative aspect ratios to antifouling efficacy was proven to be significant. An increase in aspect ratio resulted in an increase of fouling deterrence for both zoospores and cyprids. The spore density of Ulva was reduced 42% with each unit increase in aspect ratio of the Ulva-specific Sharklet AF™ topography. Similarly, the number of settled cyprids was reduced 45% with each unit increase in aspect ratio. The newly described barnacle-specific Sharklet AF™ topography (40 μm feature height, aspect ratio of 2) reduced cyprid settled by 97%. Techniques have been developed to superimpose the smaller Ulva-specific topographies onto the barnacle-specific surfaces into a hierarchical structure to repel both organisms simultaneously. The results for spore settlement on first-generation hierarchical surfaces provide insight for the efficacious design of such structures when targeting multiple settling species.

Evidence for different pharmacological targets for imidazoline compounds inhibiting settlement of the barnacleBalanus improvisus

We describe the effect of eight different imidazoline/guanidinium compounds on the settlement and metamorphosis of larvae of the barnacle Balanus improvisus. These agents were chosen on the basis of their similar pharmacological classification in vertebrates and their chemical similarity to medetomidine and clonidine, previously described as highly potent settlement inhibitors (nanomolar range). Seven of the tested compounds were found to inhibit settlement in a dose-dependent manner in concentrations ranging from 100 nM to 10 microM without any significant lethal effects. In vertebrate systems these substances have overlapping functions and interact with both alpha-adrenoceptors as well as imidazoline binding sites. Antagonizing experiments using the highly specific alpha(2)-antagonist methoxy-idazoxan or agmatine (the putative endogenous ligand at imidazoline receptors) were performed to discriminate between putative pharmacological mechanisms involved in the inhibition of cyprid settlement. Agmatine was not able to reverse the effect of any of the tested compounds. However, methoxy-idazoxan almost completely abolished the settlement inhibition mediated by guanabenz (alpha(2)-agonist, I(2) ligand), moxonidine (alpha(2)-agonist, I(1) ligand) and tetrahydrozoline (alpha-agonist, I(2) ligand). The actions of cirazoline (alpha(1)-agonist, I(2) ligand) BU 224 (I(2) ligand) and metrazoline (I(2) ligand) were not reversed by treatment with methoxy-idazoxan. These results suggest that the settlement inhibition evoked by the I(2) ligands and alpha(2)-agonists used in this study of the neurologically simple but well-organized barnacle larva is mediated through different physiological targets important in the overall settlement process.

Barnacles, limpets and periwinkles: the effects of direct and indirect interactions on cyprid settlement and success

Conventionally, direct interactions between species are considered to be the most important biological factors determining community composition, structure and stability. However, it has been suggested that the indirect interactions occurring between species may be as important. One area of ecology where the direct effects of one species on another have been well studied is in the rocky intertidal. Examination of the effect of the presence of P. vulgata (limpets) and L. littorea (periwinkles) on the settlement and development of S. balanoides (cyprids/barnacles), over a cyprid settlement season and some six months later, in four different treatments (limpets only, limpets and periwinkles combined, periwinkles only and control (no animals)) revealed the following: (1) that the presence of limpets increased cyprid settlement and recruitment success above treatments containing no limpets; (2) that cyprid settlement and success were greatest on the limpets-only treatment, followed by the limpets-and-periwinkles treatment, then by the control treatment and then by the periwinkles-only treatment; (3) that the initial effects observed in the treatments were reflected in the long-term community structure; (4) that the effects of the treatments were independent of variations in algal biomass between treatments, i.e. the effects were not indirectly mediated through a second species (host); (5) that cyprid mortality was greatest on the periwinkles-only treatment; (6) that the source of the effect of limpets on cyprid settlement appeared to originate indirectly through the action of their residual pedal mucus trails. It is concluded that periwinkles can affect the settlement and success of barnacles directly through biological disturbance (i.e. surface ablation). However, although limpets may have a direct negative effect on barnacle settlement and success, at low to medium densities, limpets can positively indirectly influence the cyprid settlement and success. This effect operates at a factor greater than that afforded by the direct negative effects of periwinkles in a mixed-species treatment. These results illustrate how the indirect effects of one species on another can have a more important structuring effect than those derived from direct effects alone.

Isethionic Acid and Floridoside Isolated from the Red Alga, Grateloupia turuturu, Inhibit Settlement of Balanus amphitrite Cyprid Larvae

Isethionic acid (2-hydroxyethane sulfonic acid) and floridoside (2-O-α-D-galactopyranosylglycerol) were extracted from the red alga, Grateloupia turuturu, and tested for anti-settlement activity against cyprid larvae of the tropical barnacle, Balanus amphitrite and for their toxicity to nauplius larvae. Isethionic acid was active for anti-settlement but had the disadvantage of being toxic to nauplius larvae. Floridoside was a potent inhibitor of cyprid settlement at non-toxic concentrations to nauplii (0.01 mg ml−1).

Topographically generated fronts, very nearshore oceanography and the distribution and settlement of mussel larvae and barnacle cyprids

Flow patterns adjacent to shore may prevent or aid shoreward migration of benthic invertebrate larvae. We hypothesized that a front at the mouth of Sunset Bay, Oregon, prevents shoreward dispersal of larvae, significantly altering settlement of mussel larvae and barnacle cyprids. Settlement was measured at three sets of moorings (three moorings per site) distributed across the front at Sunset Bay. From 6 July to 4 September 2000, samples were collected roughly every other day. Concurrently, we made vertical zooplankton tows adjacent to each mooring site and collected physical oceanographic data. During upwelling-favorable winds, the front was always present at the bay mouth, separating significantly cooler, saltier and denser offshore water from that within the bay. During downwelling winds, the front broke down and we found no significant difference in the surface physical oceanographic parameters across the bay mouth. During upwelling, the concentration of mussel larvae was higher seaward of the front than landward, but there was no significant difference in concentration during downwelling, suggesting that the front may act as a barrier to the shoreward dispersal of mussels. Mussel settlement was too low and sporadic to allow statistical analysis. There was no difference in cyprid concentrations across the bay mouth whether the front was present or not. Cyprid settlement was, however, nearly an order of magnitude lower at moorings seaward of the front than at those landward. A significant cross-correlation was found between settlement at the offshore mooring and tidal range (r=0.464, lag=0 days) and between settlement at the mid and inner moorings and downwelling winds (r=0.532 mid bay, r=0.532 inner bay, lag=0 days). Seaward of the front, settlement varied with tidal range, while landward of the front, most settlement occurred as brief pulses during downwelling winds, periods when the front was not present. We found large differences in the distribution of cyprids, and mussel larvae and cyprid settlement relative to the front; larval distributions and settlement varied with upwelling versus downwelling winds and was due to differences in the very nearshore (i.e. within 100‐1000 m of shore) coastal oceanography.

The Effect of Gregariousness in Cyprid Settlement Assays

The in vitro settlement assay using cyprids of Balanus. amphitrite is an important tool in basic and applied research. The aim of this study was to quantify the effect of gregariousness within these assays, and to determine the interaction between gregariousness and container size, and settlement promoters and inhibitors. Assays with 1, 5, 10, 15, 20, and 40 cyprids in containers with a log range of surface area to volume ratios were conducted in a fully factorial design. Assays with the same range of cyprid numbers and six concentrations of the settlement promoter 3-isobutyl-1-methylxanthine (IBMX) or the inhibitor phloroglucinol were also conducted in a fully factorial design. Percentage settlement was analysed by GLM ANOVA. Significant (p < 0.05) gregarious effects were detected at ⩾̸ 5 cyprids in a well. Surface area:volume ratio had a strong effect on cyprid settlement, but this effect could be masked by overcrowding in very small wells. Gregarious interactions between only five cyprids magnified the effect of IBMX by a factor of 10, whereas phloroglucinol had no effect without gregarious interactions. The cyprid settlement bioassay is a valuable tool for basic and applied research but must be used with care.

A Comparative Study of the Non-acidic Chemically Mediated Antifoulant Properties of Three Sympatric Species of Ascidians Associated with Seagrass Habitats

The present study investigated aspects of the antifoulant properties of three sympatric species of ascidians found in seagrass habitats of the Gulf of Mexico, Southern Atlantic Ocean, and Caribbean. Field observations in Saint Joseph Bay, Florida indicate that all three species are common and that the tunic of the solitary ascidian Molgula occidentalis is often heavily fouled, while the outer surfaces of both the colonial ascidians Amaroucium stellatum and Botryllus planus are free of fouling organisms. Antifoulant activities of a suite of increasing hydrophilic organic extracts prepared from the tunic of M. occidentalis and whole colonies of A. stellatum and B. planus were measured using both sympatric microbial (bacteria) and macroinvertebrate (cyprid larvae of Balanus amphitrite) fouling organisms in laboratory bioassays. In addition, field antifoulant assays were conducted by combining organic extracts with controlled-release resin and subsequently coating this material on to acrylic rods deployed in the field for a 72?h period. Extracts of the tunic of M. occidentalis generally did not inhibit bacterial growth. The exception was the methanol extract, which inhibited growth in one of the six marine bacteria tested. Moreover, only the highest concentrations of hexane and methanol tunic extracts tested prevented attachment of cyprid larvae. Field assays revealed no antifoulant activity on rods coated with resin containing extracts of M. occidentalis. Inhibition of both microbial growth and cyprid settlement were much more pronounced in whole-organism extracts of the two colonial ascidians. Most potent were the aqueous methanol extracts of colonies of B. planus and A. stellatum which inhibited growth in five of the six marine bacteria tested. In addition, hydrophilic and lipophilic extracts of the colonial ascidians significantly inhibited attachment of cyprid larvae, in many instances across a wide range of extract concentrations. Field antifoulant assays indicated that extracts of both colonial ascidians inhibited settlement of bryozoans and barnacles. The findings indicate that the colonial ascidians B. planus and A. stellatum possess chemical antifoulant properties. In contrast, the solitary ascidian M. occidentalis appears to either tolerate fouling or possess other non-chemical mechanisms to cope with the risks associated with epibiont overgrowth.

Barnacle larval supply to sheltered rocky shores: a limiting factor?

In northwest Europe, sheltered rocky shores are dominated by fucoid canopy algae and barnacles are rare, although the latter are extremely abundant on exposed shores. The supply of the intertidal barnacle Semibalanus balanoides (L.) to sheltered, fucoid dominated rocky shores was investigated to determine the importance of larval supply in limiting the abundance of adults in shelter. Larval supply was measured at two spatial scales, at the scale of shore (100s of metres), by comparing larval concentrations at exposed and sheltered sites, and at a smaller spatial scale (m), by examining the role of fucoid canopies in limiting supply to the substratum. Replicate plankton trawls were carried out above the intertidal zone at high water at two sheltered sites and nearby exposed headlands. The concentration of S. balanoides cyprid larvae was significantly higher at the sheltered sites on two out of three sampling occasions with up to 14 times greater larvae on one occasion than the nearby exposed site. The effect of the macroalgal canopy on supply to the substratum was assessed in two ways: directly, by pumping water from the substratum in areas with and without Ascophyllum nodosum (L.) Le Jolis, and indirectly by measuring cyprid settlement in a canopy-manipulation experiment. Pumped plankton samples from mid tide level showed that the A. nodosum canopy did not form a barrier to larval supply and may have had a positive effect on larval concentrations at the substratum. Cyprid settlement was assessed in the mid shore A. nodosum and low shore Fucus serratus L. zones to areas with canopy algae (but protected from the sweeping effects of macroalgal fronds) and without canopy. Settlement over three consecutive 24-h periods showed a consistent pattern; settlement was consistently lower beneath the F. serratus canopy than in cleared areas, suggesting that this algal species forms a barrier, limiting supply of cyprid larvae to the substratum.

UV-B damages eyes of barnacle larvae and impairs their photoresponses and settlement success.

The impact of enhanced UV-B radiation on marine ecosystems due to ozone depletion has caused growing global concern. Barnacle larvae have evolved complex photoreceptors and elaborate phototactic behaviors, which enable them to identify suitable habitats for feeding and settlement. For the first time, we demonstrate that environmentally realistic levels of UV-B radiation can induce ocular damage in barnacle larvae, thereby impairing the phototactic behavior of naupliar larvae and reducing settlement success of cypris larvae. Significant disruptions of rhabdomeres (the photosensitive structures in which phototransduction takes place) occurred in the retinular cells of naupliar eyes when naupliar larvae were exposed to a UV-B dose of 7.2 kJ m(-2), and impairment was dependent upon dose rather than irradiance. Our experimental data also showed that phototaxis of nauplii was ca. 4 times more sensitive to UV-B than settlement of cyprids. Since barnacles play an important role in the function and structure of coastal systems worldwide, any impairment of phototactic and settlement behavior of the larvae would pose a significant threat to the sustainability of this ecologically important species. The fact that enhanced UV-B radiation can induce ocular damage and subsequent phototactic impairment in barnacle larvae suggests that UV-B may also cause similar damage to other zooplankton species.

Non-toxic Antifouling Activity of Polymeric 3-alkylpyridinium Salts from the Mediterranean Sponge Reniera sarai (Pulitzer-Finali)

The antifouling activity and toxicity of polymeric 3-alkylpyridinium salts (poly-APS) isolated from the Mediterranean sponge Reniera sarai were studied. The activity of these natural products was compared to that of zinc and copper complexes of pyrithione, two non-persistent booster biocides successfully used in current antifouling coatings. Larvae of Balanus amphitrite (cyprids and nauplii) were used to monitor settlement inhibition and the extent to which inhibition was due to toxicity. The microalga Tetraselmis suecica and larvae of the mussel Mytilus galloprovincialis were used in toxicity bioassays. Compared to the booster biocides, poly-APS were less effective at inhibiting cyprid settlement, but their effects were non toxic and reversible, with very low toxicity against the organisms used in the toxicity bioassays. Although encouraging, these results are not enough to warrant the use of poly-APS as a potential commercial antifoulant. They however justify possible future efforts to chemically synthesize poly-APS analogues for further tests.

Involvement of Acetyl Choline in Settlement of Balanus amphitrite

The aim of the present study was to investigate the presence and distribution of cholinergic molecules in Balanus amphitrite cyprids and their possible involvement in settlement and adhesion. Acetylcholinesterase (AChE, the lythic enzyme of acetylcholine) activity was detected, for the first time, by biochemical and histoenzymological methods, in the thoracic muscles, gut wall and cement gland. The immunodetection of choline acetyltransferase-like (ChAT) molecules in the same area and in the neuropil of the central nervous system suggests the presence of a cholinergic innervation, and the involvement of acetylcholine in muscular contraction and cement gland exocytosis. The binding of FITC-conjugate f -bungarotoxin in the cement gland cells confirms the latter hypothesis. Acetylcholine involvement in the settlement process was also investigated by laboratory tests employing cholinergic antagonists and agonists. An increase of available acetylcholine due to the partial inhibition of AChE activity produced an increase in cyprid settlement. The data presented support the hypothesis that acetylcholine has a neurotransmitter/neuromodulator role in settlement and adhesion of barnacle cyprids.

The Effects of Foul-release Coatings on the Settlement and Behaviour of Cyprid Larvae of the Barnacle Balanus amphitrite amphitrite Darwin

Foul-release coatings are generally assumed to affect fouling of surfaces via interfering with adhesion of fouling organisms. However, the potential effects of these coatings on other aspects of the biology of fouling organisms such as behaviour have not in general been explored. The effects of wax-based foul-release coatings containing silicone oil on the settlement and behaviour of cyprid larvae of the barnacle Balanus amphitrite were studied. Settlement (as measured by metamorphosis) of cyprids was strongly inhibited on all coatings but particularly on those containing silicone oil at concentrations of 5% or more. The behaviour of cyprids was also altered on coatings containing S 5% silicone oil, with cyprids assuming an inverted position, preventing adhesion. This effect was reversible in part; when cyprids exposed to experimental coatings for 1 d were transferred to uncoated surfaces their behaviour returned to normal, except that metamorphosis did not occur. The results indicate that model foul-release coatings containing wax and silicone oil can affect settlement and behaviour, as well as adhesion.

Role of post-settlement mortality and 'supply-side' ecology in setting patterns of intertidal distribution in the chthamalid barnacles Chthamalus montagui and C. stellatus

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 249:207-214 (2003) - doi:10.3354/meps249207 Role of post-settlement mortality and Œsupply-side¹ ecology in setting patterns of intertidal distribution in the chthamalid barnacles Chthamalus montagui and C. stellatus J. Delany1,*, A. A. Myers2, D. McGrath3, R. M. O¹Riordan2,4, A. M. Power2 1Dove Marine Laboratory, Department of Marine Sciences and Coastal Management, University of Newcastle upon Tyne NE30 4PZ, United Kingdom 2Department of Zoology and Animal Ecology, University College Cork, Lee Maltings, Prospect Row, Cork, Ireland 3Department of Life Sciences, Galway-Mayo Institute of Technology, Galway, Ireland 4Department of Biological Sciences, National University of Singapore, 117543 Singapore *Email: j.e.delany@ncl.ac.uk ABSTRACT: The chthamalid barnacles Chthamalus montagui and C. stellatus occupy distinctive distributional patterns on European rocky shores. To explore whether these patterns are determined primarily by larval settlement or by post-settlement mortality, we examined the abundance of each species from cyprid attachment through successive stages in its intertidal life history and thus attempted to determine the critical stage for the establishment of adult patterns of dominance. Sampling was carried out on 4 shores in Cork, SW Ireland. On 2 of the shores, sampling sites were in zones in the upper shore dominated by C. montagui, and on the other 2 shores, sites were in zones in the midshore dominated by C. stellatus. The patterns of cyprid settlement and recruitment of early metamorphs in these zones did not reflect that of adult abundances. Patterns of mortality of the 2 species were determined from photographs. Mortality of recruits between 6 and 12 mo after settlement differed between the 2 zones. Mortality of C. montagui was higher than that of C. stellatus in the midshore zone, while the reverse trend was observed in the upper C. montagui-dominated zone, with C. stellatus recruits suffering higher rates of mortality than those of C. montagui. Post-settlement mortality, rather than larval supply, was therefore deemed to be the more significant factor in determining the characteristic patterns of these chthamalid species on SW Ireland shores. KEY WORDS: Larval supply · Post-settlement mortality · Chthamalus montagui · C. stellatus Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 249. Online publication date: March 10, 2003 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2003 Inter-Research.

The bioactivity of bacterial isolates in Hong Kong waters for the inhibition of barnacle ( Balanus amphitrite Darwin) settlement

Three bacterial isolates ( Micrococcus sp., Rhodovulum sp., and Vibrio sp.) from natural biofilms were investigated for their effects on cyprid settlement of Balanus amphitrite in laboratory bioassays. The inhibitive effect of these bacteria was clearly demonstrated by using a choice assay, in which cyprids settled preferentially on surfaces without bacterial pretreatment over those possessing a monospecies bacterial film. This result suggested that the inhibitive effect was mediated by direct larval contact with bacterial film surface rather than the perception of diffusible bacterial products. In a no-choice assay, monospecies bacterial films of different cell densities reduced cyprid settlement in a density-dependent manner. Vibrio sp. was the most potent inhibitor among the three isolates as it effectively inhibited cyprid settlement by relatively low-density films. The cells of Vibrio sp. were the smallest among the three isolates, suggesting that the correlation between bacterial cell density and cyprid settlement might not be merely due to the reduction of free-space availability. For all three isolates, films that were killed by formaldehyde or UV treatment were as potent as untreated, live films. These films remained inhibitive even in the presence of a strong promoter for cyprid settlement, namely conspecific settlement factor (SF), obtained from adult B. amphitrite. However, SF reverted the inhibitive effect of natural biofilms developed in the intertidal region.

Larval settlement behaviour of the barnacle Balanus reticulatus in the laboratory

The effect of algal food concentration, substratum, light, salinity, cyprid density and ‘footprints’, cyprid age, films of organic biopolymers, bacteria and diatoms on the settlement of Balanus reticulatus cyprids were studied. The algal food quantity (from 7×104 to 4×105 cells ml−1) fed to nauplii had a significant effect on the settlement. Cyprids failed to settle on glass surfaces but would settle on polystyrene. Light, cyprid ‘footprints’ and age significantly affected the settlement, however, salinity (from 20 to 40 psu) and cyprid density (from 5 to 200 per 5 ml of seawater) had no effect on the settlement. Films of organic polymers, bacteria, and diatoms inhibited the settlement compared to control. It is suggested that cyprids of B. reticulatus can serve as an appropriate test material for antifouling bioassays in those areas where the former forms a dominant species.

The effect of pedal mucus on barnacle cyprid settlement: a source for indirect interactions in the rocky intertidal?

Laboratory assessment of barnacle cyprid settlement showed that it was increased by a multiple of ∼6 and by a multiple of ∼3 by the pedal mucus produced by Patella vulgata and by Littorina littorea, respectively. Field experiments showed that pedal mucus produced by P. vulgata could increase cyprid settlement by a multiple of ∼4, but that there was no effect of the pedal mucus produced by L. littorea. Evaluation of the effect of pedal mucus coated with nitro-cellulose and various pedal extracts, on cyprid settlement, ascertained that there appeared to be no chemotactic or chemotaxic effect of pedal mucus on cyprid settlement. In contrast, the use of a physical analogue to pedal mucus, silicon grease, increased cyprid settlement by a multiple of ∼18. Pedal mucus produced by P. vulgata and by L. littorea increased the time spent by cyprids in surface suitability testing by a multiple of ∼10 and ∼3, respectively. Only the pedal mucus produced by P. vulgata had any effect on the exploratory behaviour of cyprids increasing the time spent on this behaviour by a multiple of ∼3. Pedal mucus affects the settlement of cyprids through adhesive enmeshment, resulting in positive feedback to the mechanoreceptors housed in the antennules of cyprids, in what is effectively a settlement cascade. Pedal mucus produced by P. vulgata and L. littorea can affect the settlement of the majority of settling marine organisms through physical entrapment. Pedal mucus produced by L. littorea will have little, if any, effect on the settlement of organisms in the field whereas the pedal mucus produced by P. vulgata may be of major importance in determining the adult distribution patterns.

Barnacle Settlement on Hydrogels

Settlement of cultured Balanus amphitrite cyprid larvae was tested on different non-solid hydrogel surfaces. Gels consisting of alginate (highly anionic), chitosan (highly cationic), polyvinyl alcohol substituted with light-sensitive stilbazolium groups (PVA-SbQ; very low cationic) and agarose (neutral) were applied in cell culture multi-well plates. Polystyrene served as a solid surface reference. Preliminary experiments were performed to determine whether any substances leaching out of the gels could inhibit barnacle settlement. Whilst leachate from the gels revealed no toxicity towards Artemia salina nauplius larvae, PVA-SbQ in solution at and above a concentration of 0.4 ppm inhibited B. amphitrite cyprid settlement. Gels were therefore washed to avoid such effects during further testing, and toxicity and settlement tests with B. amphitrite nauplii and cyprids, respectively, applied to verify that washing was effective. Settlement was tested directly on the different test materials, followed by a quality test of non-settled larvae. All gels inhibited barnacle settlement compared to the polystyrene controls. Gels consisting of 2.5% PVA-SbQ or 0.5% agarose showed promising antifouling properties. Although some settlement occurred on 2.5% PVA-SbQ gels, metamorphosis was clearly inhibited. Only 10% of the larvae had settled on 0.5% agarose gels after 8 d. Less than 40% settlement occurred on alginate gels, as well as on 2% chitosan gels. Quality testing showed that the majority of remaining non-settled larvae in all gel experiments were able to settle when offered a suitable solid substratum.