Barnacle Settlement Research Articles

Metamorphosis in the cirripede crustacean Balanus amphitrite.

Stalked and acorn barnacles (Cirripedia Thoracica) have a complex life cycle that includes a free-swimming nauplius larva, a cypris larva and a permanently attached sessile juvenile and adult barnacle. The barnacle cyprid is among the most highly specialized of marine invertebrate larvae and its settlement biology has been intensively studied. By contrast, surprisingly few papers have dealt with the critical series of metamorphic events from cementation of the cyprid to the substratum until the appearance of a suspension feeding juvenile. This metamorphosis is both ontogenetically complex and critical to the survival of the barnacle. Here we use video microscopy to present a timeline and description of morphological events from settled cyprid to juvenile barnacle in the model species Balanus amphitrite, representing an important step towards both a broader understanding of the settlement ecology of this species and a platform for studying the factors that control its metamorphosis. Metamorphosis in B. amphitrite involves a complex sequence of events: cementation, epidermis separation from the cypris cuticle, degeneration of cypris musculature, rotation of the thorax inside the mantle cavity, building of the juvenile musculature, contraction of antennular muscles, raising of the body, shedding of the cypris cuticle, shell plate and basis formation and, possibly, a further moult to become a suspension feeding barnacle. We compare these events with developmental information from other barnacle species and discuss them in the framework of barnacle settlement ecology.

Observations on the settlement and cementation of barnacle (Balanus amphitrite) cyprid larvae after artificial exposure to noradrenaline and the locations of adrenergic-like receptors

Exploration of substrata prior to cementation and metamorphosis is a critical step in the life cycle of Cirripedes. To this end, barnacle cyprid larvae have evolved sophisticated sensory mechanisms to investigate chemical as well as topographical composition of the substratum. Since barnacles are major biofoulers, the sensory structures of Balanus amphitrite cyprids have been described in detail using ultrastructural techniques like SEM and TEM. Settlement assays have shown that cyprid settlement is deterred by adrenergic receptor agonists and antagonists, yet the exact location of these receptors on cyprid sensory structures is unknown. Here, using a fluorescent adrenergic receptor antagonist (Bodipy FL-Prazosin) with the aid of confocal microscopy we describe the putative locations of adrenergic-like receptors in B. amphitrite cyprids. Our results indicate that postaxial setae 2 and 3 of the 2nd and 3rd segments respectively, the sub-terminal setae of the 4th antennular segment and the cement gland secretory cells seem to bear the adrenergic-like receptors. Using optical and electron microscopy we further studied the effects of noradrenaline (NA), an adrenergic receptor agonist, on cyprid settlement and metamorphosis. NA treated cyprids forgo the typical settlement behavior and metamorphose into juvenile barnacles without cementing to the substratum. Cyprid-barnacle metamorphosis in NA treated cyprids is also prolonged as compared to untreated barnacles. The key role played by adrenergic-like receptors during surface sensing, cementation and metamorphosis is discussed.

Comparative Glycoproteome Analysis: Dynamics of Protein Glycosylation during Metamorphic Transition from Pelagic to Benthic Life Stages in Three Invertebrates

The life cycle of most benthic marine invertebrates has two distinct stages: the pelagic larval stage and the sessile juvenile stage. The transition between the larval stage and the juvenile stage is often abrupt and may be triggered by post-translational modification of proteins. Glycosylation, a very important post-translational modification, influences the biological activity of proteins. We used two-dimensional gel electrophoresis (2-DE) followed by glycoprotein-specific fluorescence staining and mass spectrometry with the goal of identifying glycosylation pattern changes during larval settlement and metamorphosis in barnacles, bryozoans, and polychaetes. Our results revealed substantial changes in the protein glycosylation patterns from larval to juvenile stages. Before metamorphosis, the degree of protein glycosylation was high in the barnacle Balanus (=Amphibalanus) amphitrite and the spionid polychaete Pseudopolydora vexillosa, whereas it increased after metamorphosis in the bryozoan Bugula neritina. We identified 19 abundant and differentially glycosylated proteins in these three species. Among the proteins, cellular stress- and metabolism-related proteins exhibited distinct glycosylation in B. amphitrite and B. neritina, whereas fatty acid metabolism-related proteins were abundantly glycosylated in P. vexillosa. Furthermore, the protein and gene expression analysis of some selected glycoproteins revealed that the degree of protein glycosylation did not always complement with transcriptional and translational changes associated with the larval-juvenile transition. The current study provides preliminary information on protein glycosylation in marine invertebrates that will serve as a solid basis for future comprehensive analysis of glycobiology during larval settlement and metamorphosis.

Numerical simulations of barnacle larval dispersion coupled with field observations on larval abundance, settlement and recruitment in a tropical monsoon influenced coastal marine environment

Larval abundance in an area depends on various factors which operate over different spatial and temporal scales. Identifying the factors responsible for variations in larval supply and abundance is important to understand the settlement and recruitment variability of their population in a particular area. In view of this, observations were carried out to monitor the larval abundance, settlement and recruitment of barnacles on a regular basis for a period of two years. The results were then compared with the numerical modelling studies carried out along the west coast of India. Field observations of larval abundance showed temporal variations. The least abundance of larvae was mostly observed during the monsoon season and the peak in abundance was mostly observed during the pre-monsoon season. Numerical simulations also showed a seasonal change in larval dispersion and retention patterns. During pre-monsoon season the larval movement was mostly found towards south and the larvae released from the northern release sites contributed to larval abundance within the estuaries, whereas during the monsoon season the larval movement was mostly found towards north and the larvae released from southern release sites contributed to larval abundance within the estuary. During post-monsoon season, the larval movement was found towards the north in the beginning of the season and is shifted towards the south at the end of the season, but the movement was mostly restricted near to the release sites. Larval supply from the adjacent rocky sites to the estuaries was higher during the pre-monsoon season and the retention of larvae released from different sites within the estuaries was found to be highest during the late post-monsoon and early pre-monsoon season. Maximum larval supply and retention during the pre-monsoon season coincided with maximum larval abundance, settlement and recruitment of barnacles observed in the field studies. These observations showed that the pattern of larval dispersion and retention in the region is predominantly driven by local hydrodynamics operating in the vicinity. Linking larval dispersion and retention with settlement and recruitment of barnacles indicated that the processes are mainly influenced by wind and resultant current patterns. These findings facilitate unravelling the processes operating in the region and to understand the distribution pattern of the intertidal organisms in general in this tropical environment influenced by monsoons.

Coastal upwelling is linked to temporal genetic variability in the acorn barnacle Balanus glandula

Dispersal and recruitment are central processes that shape the geographic and temporal distributions of populations of marine organisms. However, significant variability in factors such as reproductive output, larval transport, survival, and settlement success can alter the genetic identity of recruits from year to year. We designed a temporal and spatial sampling protocol to test for genetic heterogeneity among adults and recruits from multiple time points along a similar to 400 km stretch of the Oregon (USA) coastline. In total, 2824 adult and recruiting Balanus glandula were sampled between 2001 and 2008 from 9 sites spanning the Oregon coast. Consistent with previous studies, we observed high mitochondrial DNA diversity at the cytochrome oxidase I locus (884 unique haplotypes) and little to no spatial genetic population structure among the 9 sites (Phi(ST) = 0.00026, p = 0.170). However, subtle but significant temporal shifts in genetic composition were observed among year classes (Phi(ST) = 0.00071, p = 0.035), and spatial Phi(ST) varied from year to year. These temporal shifts in genetic structure were correlated with yearly differences in the strength of coastal upwelling (p = 0.002), with greater population structure observed in years with weaker upwelling. Higher levels of barnacle settlement were also observed in years with weaker upwelling (p < 0.001). These data suggest the hypothesis that low upwelling intensity maintains more local larvae close to shore, thereby shaping the genetic structure and settlement rate of recruitment year classes.

Role of conspecific cues and sugars in the settlement of cyprids of the barnacle, Balanus amphitrite

Gregarious settlement in barnacle is attributed to the settlement-inducing protein complex of cuticular glycoprotein, arthropodin. In this study, we characterized arthropodin protein complex (APC) from crude protein extracts of whole barnacle (AE), and also from soft body (SbE) and shell (ShE). The settlement of cyprids exposed to surfaces coated with different crude protein extracts and APC components was evaluated. In the natural environment, larvae are also exposed to different dissolved sugars. Therefore, the cyprids were tagged with different sugars and exposed to AE, SbE and ShE in order to elucidate their specific role in determining the way barnacle cyprids identify conspecifics. A previously undescribed 66-kDa subunit was observed in shell and soft body APC, and a 98-kDa subunit was observed in shell APC. Both the subunits were shown to inhibit settlement when alone but promoted settlement in combination (ShE), suggesting that these proteins interact in a coordinated manner. The crude adult extract (AE) facilitated higher settlement compared with shell or soft body extract. However, when cyprids were tagged with different sugars and exposed to the surfaces coated with different crude protein extracts, settlement response differed and was jointly determined by the type and concentration of sugars. Such interactions could play an important role in nature as larvae encounter surfaces covered with different glycoproteins and also experience different dissolved cues.

Antifouling activity of marine sessile organisms from China against barnacle settlement

The antifouling activity of a series of hexane, ethyl acetate, ethanol and aqueous extracts from 11 species of marine sessile organisms collected from the south-east coast of China was investigated. Settlement inhibition of cyprid larvae of the barnacleBalanus albicostatuswas used to evaluate their antifouling efficacy. Screening of the 44 extracts showed antifouling activity in 90.9% of the hexane extracts followed by 90.9% of the ethyl acetate, 72.7% of the ethanol and 36.4% of the aqueous extracts. The hexane extracts ofTubularia mesembryanthemum, Notarcus leachii cirrosusandStyela canopus, the ethyl acetate extracts ofBugula neritinaandN. leachii cirrosus,and the ethanol extracts of B. neritinaandAnthopleura sp.were the most active in inhibiting the settlement ofB. albicostatus, with EC50values all below 50 μg/ml. At least one of the four extracts of each tested species exhibited antifouling activity, suggesting that all 11 marine sessile organisms contained antifouling substances and they may have evolved chemical defences against biofouling on their surfaces.

Biofilms and Marine Invertebrate Larvae: What Bacteria Produce That Larvae Use to Choose Settlement Sites

Communities of microorganisms form thin coats across solid surfaces in the sea. Larvae of many marine invertebrates use biofilm components as cues to appropriate settlement sites. Research on the tube-dwelling polychaete worm Hydroides elegans, a globally common member of biofouling communities, is described to exemplify approaches to understanding biofilm bacteria as a source of settlement cues and larvae as bearers of receptors for bacterial cues. The association of species of the bacterial genus Pseudoalteromonas with larval settlement in many phyla is described, and the question of whether cues are soluble or surface-bound is reviewed, concluding that most evidence points to surface-bound cues. Seemingly contradictory data for stimulation of barnacle settlement are discussed; possibly both explanations are true. Paleontological evidence reveals a relationship between metazoans and biofilms very early in metazoan evolution, and thus the receptors for bacterial cues of invertebrate larvae are very old and possibly unique. Finally, despite more than 60 years of intense investigation, we still know very little about either the bacterial ligands that stimulate larval settlement or the cellular basis of their detection by larvae.

Long-term in situ observation of barnacle growth on soft substrates with different elasticity and wettability

In this paper, settlement, metamorphosis, and long term growth of barnacles on soft substrates with a wide elasticity range (modulus 0.01–0.47 MPa) as well as with the variation in wettability were investigated for the first time in vitro, in the laboratory environment. Tough double-network (DN) hydrogels and polydimethylsiloxane (PDMS) were used as the soft hydrophilic substrates and hydrophobic substrates, respectively, and polystyrene (PS), a hard and hydrophobic substrate, was used as a control. It was observed that (1) the initial settlement and metamorphosis of cyprid larvae dramatically increase with the substrate elastic modulus while not showing an explicit dependence on the substrate wettability; (2) the growth rate of barnacles on both DN gels and PDMSs does not show an explicit dependence on the elasticity of the soft substrates, while it shows a slightly higher value on the hydrophobic PDMSs than on the hydrophilic DN gels; (3) the growth rate on these soft substrates is explicitly lower than that on the rigid PS substrate at the late stage of the growth; (4) the “self-release” phenomenon of barnacles was observed for the PDMS substrate with a modulus higher than 0.01 MPa. Based on these observations, the antifouling effects of the soft substrates on barnacles were discussed.

Variation in mussel and barnacle recruitment parallels a shift in intertidal community structure in the Cook Strait region of New Zealand

Recruitment influences populations and communities of marine organisms to varying degrees and across a range of spatial scales. We hypothesised that recruitment plays a role in maintaining different intertidal invertebrate assemblages between two nearby locations in New Zealand (Wellington Harbour and the south coast), long reported to have dramatically different communities (with greater cover of sessile invertebrates in the Harbour). Sites in Wellington Harbour were hypothesised to have higher monthly recruitment rates of mussels and barnacles and greater barnacle colonisation after 1 year. Surveys were conducted to quantify community differences. In Wellington Harbour, the mid-intertidal zone was dominated by the mussel Mytilus galloprovincialis and the barnacle Chamaesipho columna and the high intertidal zone by C. columna. In contrast, on the south coast mussels were almost completely absent from both tidal heights and barnacles (predominantly Chamaesipho brunnea) were sparse. In the high zone, monthly recruitment and long term colonisation (over 1 year) of barnacles was much greater in the Harbour; in the mid-intertidal zone, mussel recruitment was up to two orders of magnitude greater in the Harbour than the south coast. Species-specific recruitment patterns differed between the locations, however and were consistent with those of adult abundance.

Noradrenaline deters marine invertebrate biofouling when covalently bound in polymeric coatings

Marine biofouling is the unwanted accumulation of marine organisms on submerged structures and ships. Attempts to develop effective marine antifouling paints and coatings have had deleterious effects on marine and aquatic ecosystems. Current research efforts for designing an effective antifouling coating are focused on understanding the biology of the fouling organisms. Prior to settlement and metamorphosis, larvae of many marine invertebrates investigate surfaces using exploratory structures bearing an array of sensory cells. Interfering with these settlement and attachment mechanisms could be a promising alternative to existing antifouling strategies. Herein, we report the innovation of “fouling deterrence”, an antifouling strategy in which marine invertebrate larval exploratory behaviors are exploited to defeat biofouling. Our approach is predicated upon larval recognition of covalently bound ligands, such as the catecholamine, noradrenaline which presents ‘unfavorable’ cues to deter larval settlement. To test this concept, we developed noradrenaline conjugated poly-HEMA (hydroxyethylmethacrylate) and poly-MAA (methacrylic acid) polymer systems. The bioactivity of covalently conjugated noradrenaline molecules was assessed using oyster hemocyte cellular assays followed by larval settlement assays using pediveliger larvae of the Eastern Oyster, Crassostrea virginica and the cyprid larvae of the barnacle, Balanus amphitrite. Noradrenaline conjugated polymer surfaces induced apoptosis in oyster hemocytes and deterred larval settlement in both oysters and barnacles.

Barnacle settlement and the adhesion of protein and diatom microfouling to xerogel films with varying surface energy and water wettability

Previous work has shown that organosilica-based xerogels have the potential to control biofouling. In this study, modifications of chemistry were investigated with respect to their resistance to marine slimes and to settlement of barnacle cyprids. Adhesion force measurements of bovine serum albumin (BSA)-coated atomic force microscopy (AFM) tips to xerogel surfaces prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl-containing precursors, indicated that adhesion was significantly less on the xerogel surfaces in comparison to a poly(dimethylsiloxane) elastomer (PDMSE) standard. The strength of adhesion of BSA on the xerogels was highest on surfaces with the highest and the lowest critical surface tensions, γC and surface energies, γS, and duplicated the ‘Baier curve’. The attachment to and removal of cells of the diatom Navicula perminuta from a similar series of xerogel surfaces were examined. Initial attachment of cells was comparable on all of the xerogel surfaces, but the percentage removal of attached cells by hydrodynamic shear stress increased with γC and increased wettability as measured by the static water contact angle, θWs, of the xerogel surfaces. The percentage removal of cells of Navicula was linearly correlated with both properties (R 2 = 0.74 for percentage removal as a function of θWs and R 2 = 0.69 for percentage removal as a function of γC). Several of the aminopropylsilyl-containing xerogels showed significantly greater removal of Navicula compared to a PDMSE standard. Cypris larvae of the barnacle B. amphitrite showed preferred settlement on hydrophilic/higher energy surfaces. Settlement was linearly correlated with θWs (R 2 = 0.84) and γC (R 2 = 0.84). Hydrophilic xerogels should prove useful as coatings for boats in regions where fouling is dominated by microfouling (protein and diatom slimes).

Natural antifoulants from the marine cyanobacterium Lyngbya majuscula

Filamentous benthic marine cyanobacteria are a prolific source of structurally unique bioactive secondary metabolites. A total of 12 secondary metabolites, belonging to the mixed polyketide–polypeptide structural class, were isolated from the marine cyanobacterium, Lyngbya majuscula, and were tested to determine if they showed activity against barnacle larval settlement. The assays revealed four compounds, dolastatin 16 (1), hantupeptin C (4), majusculamide A (10), and isomalyngamide A (12), that showed moderate to potent anti-larval settlement activities, with EC50 values ranging from 0.003 to 10.6 μg ml−1. In addition, field testing conducted over a period of 28 days (using the modified Phytagel™ method) based on the cyanobacterial compound, dolastatin 16, showed significantly reduced barnacle settlement as compared to controls at all the concentrations tested. The results of this study highlight the importance of marine cyanobacteria as an underexplored source of potential environmentally friendly antifoulants.

The influence of estuarine water quality on cover of barnacles and Enteromorpha spp.

The influence of ambient water quality on the settlement of barnacles and the green alga Enteromorpha spp. to an artificial substratum in the estuaries of Sydney, Australia, was investigated to test the efficacy of both groups of organisms as indicators of changes in water quality due to urban stormwater runoff and/or sewage overflows. Wooden settlement panels were immersed for 4months on 17 occasions between 1996 and 2005 at 11 locations known to vary in water-quality parameters (conductivity, total uncombined ammonia, oxidised nitrogen, total nitrogen, filterable phosphorus, total phosphorus, faecal coliforms and chlorophyll-a) and ambient meteorological conditions (total rainfall, maximum rainfall). Water-quality data were collected during the time that the settlement panels were deployed. Cover of barnacles was highly variable among locations (range 1.2-55.2%). Hierarchical partitioning found that chlorophyll-a, total phosphorus and total nitrogen had significant independent positive effects on barnacle cover. Together, these variables explained 26% of the variation in barnacle cover. Mean cover of Enteromorpha spp., however, did not vary significantly among locations suggesting that other potentially more important factors are influencing its settlement and growth. The results of this study suggest that barnacle cover is likely to be a useful indicator of some components of water quality.

Ecological relevance of a conspecific, waterborne settlement cue in Balanus amphitrite (Cirripedia)

Planktonic marine invertebrate larvae are now considered to exhibit varying degrees of control over their transition back to benthic habitats through behavioural and ontogenetic adaptations. Gregarious settlement in barnacles is attributed to the settlement-inducing protein complex (SIPC), the cypris larva temporary adhesive and a waterborne cue; the latter obtained by conditioning seawater with adult Balanus amphitrite (= Amphibalanus amphitrite). By responding to a waterborne settlement cue, a swimming larva may elect to settle without contacting a surface. The evidence for such a role is, however, limited. This theme is examined here by evaluating the behavioural response of cyprids to the cue through various laboratory techniques – settlement assays, motion tracking and enumeration of antennule movements – and linking the cue to recruitment of larvae in the field. The cue is detected in solution, remains active upon dilution, induces a similar response in young and aged larvae, and only a brief (3–15 min) exposure to conditioned seawater is required to stimulate settlement. Seawater collected in situ, close to piling fouled with B. amphitrite at Duke University Marine Laboratory, North Carolina, induced settlement over samples collected at a distance from the piling. The evidence derived from experiments on laboratory-conditioned and field-collected seawater is consistent with an important role for the waterborne cue in the settlement of barnacle cypris larvae.

Supply-side ecology, barnacle recruitment, and rocky intertidal community dynamics: Do settlement surface and limpet disturbance matter?

The supply of new recruits can be a critical determinant of community structure, but estimating recruitment density can be challenging due to variation in larval supply, settlement, substratum, species interactions and physical stresses. We evaluated the effect of surface type and limpet “bulldozing” on settlement and recruitment of barnacles, using replicated field experiments sampled monthly at each of four sites along the central Oregon coast in 2001, 2003, and 2008. A particular goal was to evaluate the efficacy of Saf-T-Walk, a widely used textured surface, in quantifying actual patterns and levels of recruitment. In 2001 and 2003 experiments, surfaces were bare rock (ROCK) and Saf-T-Walk (STW). In 2008 experiments, to further evaluate the influence of surface rugosity, we added two additional artificial substratum types — smooth PVC plates (no texture) and travertine plates (TRAV, low texture). Limpet activity was manipulated using barriers of anti-fouling paint. Results indicated the overwhelming importance of surface texture. Recruitment density was highest in 2001, lower in 2003, and lowest in 2008. Recruitment on STW, the most textured surface, ranged up to 87 times greater than on ROCK, and the rank order of surfaces for recruitment density was STW > ROCK > TRAV > PVC which matches that for texture. Settlement differences were even greater, with up to 1180-fold higher settlement on STW than ROCK. Limpets usually had a negative effect on recruitment of Balanus glandula on ROCK, likely due to bulldozing and direct consumption, but had a positive effect on STW. These impacts were reduced or negated when recruitment density was higher (e.g., 2001) or lower than average (e.g., 2008). Limpets had no consistent effect on Chthamalus dalli. Abundances of settlers and recruits on the different surfaces were positively correlated (explaining up to 71% of the variance), and correlations between STW and other surfaces generally were stronger in the absence of limpets. Although compared to bare rock, recruitment to STW overestimates absolute rates of recruitment, use of STW settlement plates provides an effective and relatively efficient means of determining spatial and temporal patterns of recruitment at local to geographic scales.

Effects of solar radiation on barnacle settlement, early post-settlement mortality and community development in the intertidal zone

We examined the role of solar radiation, and particularly the role of ultraviolet radiation (UVR), in regulating small-scale settlement patterns and early post-settlement mortality in the barna- cle Balanus glandula, as well as community development of sessile organisms colonizing the upper mid-intertidal zone. Settlement of B. glandula cyprids was similar in treatments with and without UVR, suggesting that UVR does not directly influence site selection by cyprids. Once attached, mor- tality during the 1 to 2 d period from attachment to metamorphosis ranged from 60 to 100%, and half of the settlers that did metamorphose died during the following 5 d. Mortality during the period from attachment to metamorphosis was significantly lower in locations protected from UVR than in loca- tions exposed to the full spectrum of solar radiation, but only by ca. 10%. Furthermore, UVR expo- sure had no detectable effect on the mortality rate of metamorphosed early juveniles. Ambient UVR levels also appear to have had little effect on the colonization of mid-intertidal habitats by sessile organisms: our study locations were colonized by 2 sessile invertebrate species and 2 algal species over a period of 2.5 mo in mid-summer, and densities of these species were similar in treatments with and without UVR. Nevertheless, solar radiation dose explained 43 to 65% of the variation in mortal- ity among daily cohorts of B. glandula, and daily cohort mortality was often 100% during periods with the highest doses. This relationship between solar radiation and survival to metamorphosis was likely due to the effect of solar radiation on desiccation and heat stress. The high sensitivity of early post- settlement mortality rates to solar radiation suggests global climate change may significantly alter patterns of survivorship through this critical stage of life.

Spatial patterns of barnacle settlement in central Chile: Persistence at daily to inter-annual scales relative to the spatial signature of physical variability

Recruitment patterns of coastal species with complex life cycles are heavily influenced by physical variability in the coastal ocean. Spatial and temporal patterns of variability in rates of larval settlement may provide clues as to the processes that drive their transport and onshore delivery, as well as variation in the supply side of population dynamics. Over 3 consecutive seasons (2006–2008), the settlement of three intertidal barnacles (the chthamaloids Jehlius cirratus and Notochthamalus scabrosus, and the balanoid Notobalanus flosculus) was monitored daily at 5 to 6 sites spread over ca. 10 km around the bay of Cartagena in central Chile, and over periods of 48, 71 and 53 consecutive days that encompassed the settlement season of these species. This sampling effort yielded settlement data with an unprecedented combination of temporal resolution and spatial coverage, which allowed us to assess and compare: (1) spatial patterns of settlement and their persistence over scales of days within each season, (2) inter-annual variation in pattern persistence, and (3) the relationship between such variation and inter-annual changes in spatial patterns of sea surface temperature (SST) variability over synoptic and high-frequency scales. While on average the spatial pattern of settlement in chthamaloids became less persistent from 2006 to 2008, the settlement pattern of N. flosculus across sites remained persistent regardless of inter-annual changes in mean settlement rates. Within seasons, the spatial patterns of settlement of N. flosculus were persistent over scales of at least 15 days, whereas for chthamaloids a spatially ordered pattern of settlement in 2006 disappeared in subsequent years. Together, these results suggest that spatially structured processes that drive larval transport, and which can vary from year to year, may have played a greater role in shaping settlement patterns of chthamaloids versus balanoids. Synoptic-scale SST variability (i.e. days) exhibited spatial structure that was highly persistent within all three seasons. Although high-frequency SST variability (i.e. hours) has been associated to onshore larval transport within the study region, its among-site patterns were not as persistent as the daily ones. Since neither synoptic-scale nor high-frequency processes shaping patterns of physical variability are sufficient to explain inter-annual variability in patterns of larval settlement, more complex physical–biological interactions must be examined. We suggest that inter-annual changes in the pattern of wind forcing relative to local topography, and the thermal structure that results from such interaction, might be related to whether the spatial structure of barnacle settlement is persistent or fluctuating within a given season. We discuss the limitations of inferences that can be made regarding transport processes from time series of larval settlement, and the insights that can be gained by focusing on the variability of spatial patterns rather than temporal changes at individual sites.

Colonization of an artificial reef in south-west England—ex-HMS ‘Scylla’

An ex-Royal Navy frigate, HMS ‘Scylla’, was placed on the seabed in Whitsand Bay, south Cornwall on 27 March 2004. After five years, the reef supported a mature steel wreck community. The colonization of the reef showed wide fluctuations in species abundance in the first two years but, by 2006, most species that dominated or characterized the reef after five years had settled. Significant colonization events included settlement of barnacles, tubeworms and hydroids within a month and remarkably high settlements of the sea urchin Psammechinus miliaris and the queen scallop Aequipecten opercularis in the first year together with starfish Asterias rubens, solitary sea squirts and ephemeral algae. The plumose anemone Metridium senile, a characteristic species of wrecks, arrived in late summer 2004 but the widely distributed dead man's fingers Alcyonium digitatum was not observed until spring 2005. Wrasse were slow to colonize the reef but were established in small numbers by the end of 2007. Sea fans, Eunicella verrucosa, were first observed in August 2007. The species count for the reef stood at 263 taxa by the end of March 2009. The inside of the reef remained poorly colonized even after five years. Areas coated with tributyltin (TBT) antifouling paint only had colonization where the paint had flaked-off or on non-toxic paint markings, but with some indication that colonization may be occurring by a very few species especially near to non-TBT areas. Many species characteristic of natural reefs had not settled and neither do they occur on older wrecks including branching axinellid sponges, some cushion sponges and the yellow cluster anemone Parazoanthus axinellae. The artificial reef developed a community that was distinctly different to nearby natural rock reefs and such artificial structures should not be considered as a replacement for damaged or destroyed natural habitats.

Barnacle repellent nanostructured surfaces formed by the self-assembly of amphiphilic block copolymers

Well-defined nanostructured surface with domains of dimension ∼20 nm was formed by the self-assembly of brush-type amphiphilic block copolymers of poly[poly(ethylene glycol)methyl ether methacrylate]-block-poly(2,3,4,5,6-pentafluorostyrene) (P(PEGMA)-b-PPFS) which demonstrate promise in discouraging barnacle settlement as proven using laboratory settlement assays and marine field tests.