Measurement of the Adhesion Force of a Living Sessile Organism on Antifouling Coating Surfaces Prepared with Polysulfobetaine-Grafted Particles

An antifouling polymer brush-like structure was fabricated by a simple and versatile dip-coating method of sulfobetaine containing copolymer-grafted silica nanoparticles (SiNPs) and alkyl diiodide cross-linkers. Surface-initiated atom transfer radical copolymerization of 3-(N-2-methacryloyloxyethyl-N,N-dimethyl)ammonatopropanesulfonate (MAPS) and N,N-dimethylaminoethyl methacrylate (DMAEMA) was carried out from initiator-immobilized SiNPs to give poly(MAPS-co-DMAEMA)-grafted SiNPs (MAPS/DMAEMA = 9/1, mol/mol) with diameters of 150-170 nm. The SiNP-g-copolymer/2,2,2-trifluoroethanol solution was dip-coated on silicon and glass substrates. Successive treatment with 1,4-diiodobutane in methanol gave a hydrophilic cross-linked coating film for the SiNP-g-copolymer. The cross-linked particle brushes did not peel off from the substrate even after washing with water in an ultrasonic cleaner despite the simple physical absorption of the SiNP-g-copolymer on the substrate surface. The adhesion force of the tentacle of a living barnacle cyprid on a glass surface covered with the cross-linked SiNP-g-copolymer was directly measured by scanning probe microscopy in seawater. The coating film exhibited extremely low adhesion to the cypris larva in the seawater, expecting this to be an effective antifouling property.

Conditioning of metal surfaces enhances Shewanella chilikensis adhesion

Microbiologically influenced corrosion and biofouling of steels depend on the adsorption of a conditioning film and subsequent attachment of bacteria. Extracellular deoxyribonucleic acid (eDNA) and amino acids are biologically critical nutrient sources and are ubiquitous in marine environments. However, little is known about their role as conditioning film molecules in early biofilm formation on metallic surfaces. The present study evaluated the capacity for eDNA and amino acids to form a conditioning film on carbon steel (CS), and subsequently, the influence of these conditioning films on bacterial attachment using a marine bacterial strain. Conditioning films of eDNA or amino acids were formed on CS through physical adsorption. Biochemical and microscopic analysis of eDNA conditioning, amino acid conditioning and control CS surfaces demonstrated that organic conditioning surfaces promoted bacterial attachment. The results highlight the importance of conditioning the surface in initial bacterial attachment to steel.

Transcriptome analyses suggest a molecular mechanism for the SIPC response of Amphibalanus amphitrite

Barnacles are notorious marine fouling organisms. Their successful attachment to a substrate requires that they search for an appropriate habitat during their cyprid stage. A chemical cue called SIPC (Settlement-Inducing Protein Complex) has been shown to play a key role in the induction of cyprid gregarious settlement; however, the underlying biochemical mechanism remains unclear. Here, RNA-seq was used to examine the gene expression profiles of Amphibalanus amphitrite cyprids in response to SIPC and to identify SIPC-activated intracellular signaling pathways. A total of 389 unigenes were differentially expressed in response to SIPC, and cement protein genes were not among them. KEGG enrichment analysis suggested that SNARE interactions in the vesicular transport pathway were significantly influenced by SIPC treatment, indicating a possible role for SIPC in triggering protein transportation and secretion. Several genes with specific functions in metamorphosis were found among the differentially expressed genes (DEGs). GO (Gene Ontology) enrichment analysis revealed that the DEGs were significantly enriched in enamel mineralization pathways, suggesting that SIPC may also be involved in the activation of mineralization.

Love at First Taste: Induction of Larval Settlement by Marine Microbes

Marine biofilms are composed of many species of bacteria, unicellular algae, and protozoa. Biofilms can induce, inhibit, or have no effect on settlement of larvae and spores of algae. In this review, we focus on induction of larval settlement by marine bacteria and unicellular eukaryotes and review publications from 2010 to September 2019. This review provides insights from meta-analysis on what is known about the effect of marine biofilms on larval settlement. Of great interest is the impact of different components of marine biofilms, such as bacteria and diatoms, extracellular polymeric substances, quorum sensing signals, unique inductive compounds, exoenzymes, and structural protein degradation products on larval settlement and metamorphosis. Molecular aspects of larval settlement and impact of climate change are reviewed and, finally, potential areas of future investigations are provided.

Quantitative analysis of the complete larval settlement process confirms Crisp's model of surface selectivity by barnacles

For barnacle cypris larvae at the point of settlement, selection of an appropriate surface is critical. Since post-settlement relocation is usually impossible, barnacles have evolved finely tuned surface-sensing capabilities to identify suitable substrata, and a temporary adhesion system for extensive surface exploration. The pattern of exploratory behaviour appears complex and may last for several hours, imposing significant barriers to quantitative measurement. Here, we employ a novel tracking system that enables simultaneous analysis of the larval body movement of multiple individuals over their entire planktonic phase. For the first time, to our knowledge, we describe quantitatively the complete settlement process of cyprids as they explore and select surfaces for attachment. We confirm the 'classic' behaviours of wide searching, close searching and inspection that comprise a model originally proposed by Prof. Dennis Crisp FRS. Moreover, a short-term assay of cyprid body movement has identified inspection behaviour as the best indicator of propensity to settle, with more inspection-related movements occurring in conditions that also promote higher settlement. More than half a century after the model was first proposed by Crisp, there exists a precise method for quantifying cyprid settlement behaviour in wide-ranging investigations of barnacle ecology and applied studies of fouling management.

Chemical Ecology of Wave-Swept Shores: the Primacy of Contact Cues in Predation by Whelks

Wave-swept shores are valuable for developing and testing key ecological principles. A synthesis of research is nonetheless missing a critical component: the chemosensory basis for behavioral interactions that determine population- and community-wide attributes. Chemical signaling environments on wave-swept shores, given their intense, turbulent mixing and complex topographies, would be difficult or impossible to simulate in a laboratory setting. For this reason, appropriately scaled field studies are needed to advance understanding of chemical stimuli and their biotic effects. Here, we performed a field investigation to establish the relative roles of dissolved and contact cues in predation by whelks (Acanthinucella spirata) on barnacles (Balanus glandula), their preferred prey. Experiments tested responses of whelks to seawater drawn above dense prey patches (10,240-12,180 barnacles m^-2) and also over adjacent sand flats (no prey present). There was no evidence of waterborne stimuli associated with prey, even when sea states were nearly tranquil. Field trials also tested faux prey, which were constructed from cleaned barnacle shells and flavored gels. Prospective contact cues were presented to whelks at concentrations typical of epidermal tissue and cuticle in live, intact barnacles. These compounds were highly effective inducers of attack behavior and feeding. Selective enzyme degradations showed that the bioactive material was proteinaceous. Moreover, whelks did not distinguish faux barnacles with a single, purified glycoprotein (named "MULTIFUNCin") from live counterparts. Combined field results thus demonstrate the importance of contact cues, and indicate little, if any, effect of waterborne cues on predation by whelks under native conditions. Our findings underscore the need for appropriately scaled field experiments, and highlight surface chemistry as a critical factor that drives trophic interactions on rocky, wave-swept shores.

A multifunctional chemical cue drives opposing demographic processes and structures ecological communities

Foundation species provide critical resources to ecological community members and are key determinants of biodiversity. The barnacle Balanus glandula is one such species and dominates space among the higher reaches of wave-swept shores (Northeastern Pacific Ocean). This animal produces a cuticular glycoprotein (named "MULTIFUNCin") of 199.6 kDa, and following secretion, a 390 kDa homodimer in native form. From field and lab experiments, we found that MULTIFUNCin significantly induces habitat selection by conspecific larvae, while simultaneously acting as a potent feeding stimulant to a major barnacle predator (whelk, Acanthinucella spirata). Promoting immigration via settlement on the one hand, and death via predation on the other, MULTIFUNCin drives opposing demographic processes toward structuring predator and prey populations. As shown here, a single compound is not restricted to a lone species interaction or sole ecological function. Complex biotic interactions therefore can be shaped by simple chemosensory systems and depend on the multifunctional properties of select bioactive proteins.

Barnacle biology before, during and after settlement and metamorphosis: a study of the interface

Mobile barnacle cypris larvae settle and metamorphose, transitioning to sessile juveniles with morphology and growth similar to adults. Because biofilms exist on immersed surfaces on which they attach, barnacles must interact with bacteria during initial attachment and subsequent growth. The objective of this study was to characterize the developing interface of the barnacle and substratum during this key developmental transition to inform potential mechanisms that promote attachment. The interface was characterized using confocal microscopy and fluorescent dyes to identify morphological and chemical changes in the interface and the status of bacteria present as a function of barnacle developmental stage. Staining revealed patchy material containing proteins and nucleic acids, reactive oxygen species amidst developing cuticle, and changes in bacteria viability at the developing interface. We found that as barnacles metamorphose from the cyprid to juvenile stage, proteinaceous materials with the appearance of coagulated liquid were released into and remained at the interface. The patchy material was associated with cuticle expansion and separation during later stages of metamorphosis, and spanned the entire vertical interface in the gap between the juvenile base and the substratum. It stained positive for proteins, including phosphoprotein, as well as nucleic acids. Regions of the developing cuticle and the patchy material itself stained for reactive oxygen species. Bacteria were absent until the cyprid was firmly attached, but populations died as barnacle development progressed. The oxidative environment may contribute to the cytotoxicity observed for bacteria and has potential for oxidative crosslinking of cuticle and proteinaceous materials at the interface.

Peptide-mediated behaviors in marine organisms Evidence for a common theme

Biology has many common themes such as DNA, RNA, the other biopolymers, and their building blocks. Chemical communication systems have similar common themes. An example is the common usage of amino acids, sugars, and nucleotides as food cues. It is likely that communication systems began with the evolution of specific meanings for preexisting molecules. One class of molecules used in specific communication is peptides. These peptides are generated as part of the body odor of organisms in aquatic environments and can act at a distance or by contact. Evidence is given for a common type of peptide receptor system. Four peptide-mediated behaviors, three in diverse crustacean groups and one in a mollusc, are discussed. The behaviors are of major survival importance, are cued by nanomolar concentrations of peptides generated by serine proteases, and the basic carboxy terminal amino acid is required. The behaviors include attraction to new shells, attraction to living prey, release of larvae, and induction of larval settlement behavior. Studies with pure di- and tripeptides show the same molecules evoke larval release behavior, shell attraction responses, and larval settlement behavior. The pure compounds are effective at nanomolar or lower concentrations. Similar peptides function as specific cues in vertebrates in response to wounding. Thus, peptide communication using serine protease-generated peptides appears to be a common theme.

Bacterial-barnacle interaction: Potential of using juncellins and antibiotics to alter structure of bacterial communities

In preparation for studies using natural products to probe interactions between bacterial consortia and settlement stage barnacles, we isolated 16 strains of bacteria associated with barnacles and examined: (1) effects of films of bacterial isolates on barnacle settlement, and (2) bacteriostatic effects of juncellins and standard antibiotics. Bacteria were isolated from the biofilm associated withBalanus amphitrite. On the basis of morphological and biochemical characteristics, bacteria were classified into five major groups:Aeromonas, Alcaligenes, Flavobacterium, Pseudomonas, andVibrio. Barnacle settlement was inhibited by allVibrio films and 64% of the other isolates. No film stimulated barnacle settlement. Juncellins were approximately as potent as standard antibiotics for all bacterial species tested.Vibrio spp. were most resistant to juncellins.

Habitat Selection and Animal Distribution in the Sea: the Evolution of a Concept

This paper considers the evolution of the concept that the local distribution of animals in the sea is largely determined by the habitat preferences and behaviour of the animals themselves. Examples are mainly taken from studies on invertebrate animals. Nineteenth-century investigations on the behavioural responses of micro-organisms to such variables as light, salinity and oxygen, stimulated analogus investigations on the behaviour of marine invertebrates. From 1920 onwards, various lines of research have developed, notably on the settlement of marine larvae, but also on habitat selection by adult planktonic and benthic invertebrates, and on host finding by parasites and commensals.

Attention has been drawn to the relevance of genetic studies on behaviour, and to the significance of investigations on terrestrial animals. A synoptic view of habitat selection has been advanced in which animals respond to a complex of interacting stimuli from their physical, chemical and biological environment.

Simple models have been presented which consider the influence of dilution of the preferred habitat by less preferred alternatives, alteration of the rate of change of a habitat, the relation between habitat preferences and lethal limits, and the colonisation of new habitats.

Modulation of barnacle (Balanus amphitrite Darwin) cyprid settlement behavior by sulfobetaine and carboxybetaine methacrylate polymer coatings

Zwitterionic polymers such as poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine methacrylate) (polyCBMA) have demonstrated impressive fouling-resistance against proteins and mammalian cells. In this paper, the effects of these surface chemistries on the settlement and behavior of an ubiquitous fouling organism, the cypris larva of the barnacle Balanus amphitrite (=Amphibalanus amphitrite), were studied in the laboratory. Conventional settlement assays and behavioral analysis of cyprids using Noldus Ethovision 3.1 demonstrated significant differences in settlement and behavior on different surfaces. Cyprids did not settle on the polySBMA or polyCBMA surfaces over the course of the assay, whereas settlement on glass occurred within expected limits. Individual components of cyprid behavior were shown to differ significantly between glass, polySBMA and polyCBMA. Cyprids also responded differently to the two zwitterionic surfaces. On polySBMA, cyprids were unwilling or unable to settle, whereas on polyCBMA cyprids did not attempt exploration and left the surface quickly. In neither case was toxicity observed. It is concluded that a zwitterionic approach to fouling-resistant surface development has considerable potential in marine applications.

Marine glycobiology: current status and future perspectives

Glycobiology, which is the study of the structure and function of carbohydrates and carbohydrate containing molecules, is fundamental to all biological systems.Progress in glycobiology has shed light on a range of complex biological processes associated with, for example,disease and immunology, molecular and cellular communication,and developmental biology. There is an established,if rather modest, tradition of glycobiology research in marine systems that has primarily focused on reproduction,biofouling, and chemical communication. The current status of marine glycobiology research is primarily descriptive with very limited progress on structural elucidation and the subsequent definition of precise functional roles beyond a small number of classical examples, e.g., induction of the acrosome reaction in echinoderms. However, with recent advances in analytical instrumentation, there is now the capacity to begin to characterize marine glycoconjugates,many of which will have potential biomedical and biotechnological applications. The analytical approach to glycoscience has developed to such an extent that it has acquired its own "-omics" identity. Glycomics is the quest to decipher the complex information conveyed by carbohydrate molecules--the carbohydrate code or glycocode. Due to the paucity of structural information available, this article will highlight the fundamental importance of glycobiology for many biological processes in marine organisms and will draw upon the best defined systems. These systems therefore may prove genuine candidates for full carbohydrate characterization.

Establishment and succession of an epibiotic community on chromated copper arsenate-treated wood in Mediterranean waters

Colonization and succession of an epibiotic animal community on chromated copper arsenate (CCA)-treated wood were studied for 18 months in the eastern Mediterranean (Saronikos Gulf, Aegean Sea). Pine wood panels, 200 x 100 x 25 mm, impregnated with CCA at retentions of 0, 12, 24, and 48 kg m(-3) were used. The abundance or surface coverage of the most characteristic taxa (polychaetes, mollusca, crustacea bryozoa, sponges, ascidians) was measured in situ, while 12 months after submersion two panels of each retention were removed and examined in the laboratory. A total of 26 taxa were identified, among which polychaetes of the family Serpulidae dominated. The controls carried the largest number of species (17) but the lowest number of individuals. On panels with CCA retentions of 12 and 24 kg m(-3), 14 and 16 species were observed, respectively, while at 48 kg m(-3), only 9 species were found. Only the controls were affected by boring bivalves of the family Teredinidae and started to break up within 3 months of submersion. Statistically significant differences in barnacle and polychaete abundance were found between treated and untreated panels. There were no significant differences among panels treated at the three CCA loadings. Ordination by nonmetric multidimensional scaling showed a seasonal effect on the colonization of the treated panels, with the highest recruitment during the warmer months of the study.

Quantifying the exploratory behaviour of Amphibalanus amphitrite cyprids

The behavioural response of cypris larvae from A. amphitrite (=Balanus amphitrite) exploring three model glass surfaces is quantified by close-range microscopy. Step length and step duration measurements reveal a response to both surface properties and flow. Without flow, 2-day-old cyprids took larger steps with shorter step duration on hydrophilic glass surfaces (bare and NH2-treated) vs hydrophobic glass (CH3-treated). These parameters suggest a more detailed, local inspection of hydrophobic surfaces and a more extensive exploration for hydrophilic surfaces. Cyprids under flow took longer steps and exhibited shorter probing times on hydrophobic glass. On hydrophilic glass, cyprids increased their step duration under flow. This active response is attributed to drag and lift forces challenging the cyprids' temporary anchoring to the substratum. Seven-day-old cyprids showed almost no discrimination between the model surfaces. Microscopic-scale observation of cyprid exploration is expected to provide new insights into interactions between cyprids and surfaces.

Purification and partial amino acid sequence analysis of the larval settlement-inducing pheromone from adult extracts of the barnacle, Balanus amphitrite (=Amphibalanus amphitrite)

A previously undescribed larval settlement-inducing protein was purified from adult extracts of the barnacle, Balanus amphitrite (=Amphibalanus amphitrite). Results of SDS-PAGE indicated that the relative molecular mass of the protein in reduced and denatured form is 31,600 +/- 500 kDa, and that it is distinct from the Settlement Inducing Protein Complex (SIPC) which has previously been determined as a larval settlement-inducing pheromone. The N-terminal 33-residue sequence of the intact protein showed no similarity with previously reported proteins in the EMBL/Genbank/DDBJ databases. The purified protein at a concentration of 10 microg ml(-1) induced approximately four times more larval settlement than the control (filtered natural seawater). In addition, results of the assay using both 24-well polystyrene plates and agarose gels indicated that this protein is probably released into seawater and attracts cypris larvae. These results suggest that the purified protein is a waterborne type pheromone which induces settlement of larvae of B. amphitrite.

Interaction of conspecific cues in Balanus amphitrite Darwin (Cirripedia) settlement assays: continued argument for the single-larva assay

Gregariousness in marine invertebrate larvae is an important regulator of benthic community structure. Previous laboratory settlement assays employing Balanus amphitrite Darwin cyprids found gregarious effects with as few as 3 larvae well(-1), together with modulation of such effects by chemical cues. Here, the relationship between settlement rate and larval density was rigorously tested through a fully randomised design. Seawater conditioned with adult B.amphitrite was tested alongside unconditioned seawater to determine the effect of a conspecific cue on gregarious interactions. Gregarious effects were detected in both conditioned and unconditioned seawater at < or =4 larvae well(-1). In untreated seawater, settlement rate increased linearly with larval density, levelling off at densities of > or =10 larvae well(-1). In conditioned seawater, settlement induction was observed at < or =4 larvae well(-1), switching to inhibition at 6, 8 and 10 larvae well(-1), before asymptoting at the highest densities tested. These results advocate the use of individual larvae in laboratory assays that investigate factors stimulating barnacle settlement.

Field-based video observations of wild barnacle cyprid behaviour in response to textural and chemical settlement cues

Many marine invertebrate larvae respond behaviourally to environmental settlement cues, yet behaviours are often only inferred from settlement patterns or are limited to laboratory studies. The behaviour of wild cypris larvae of Semibalanus balanoides L. was filmed on settlement tiles in the field. Tiles were of five different textures with a nested treatment of crude conspecific adult extract (AE). The effects of texture and AE on eleven defined behaviours were analysed. Texture affected the gross and net exploratory distances, velocity, acceleration and time spent exploring. AE attracted more cyprids during the first minute of immersion and increased the time spent on surfaces. Relatively few arrivals that either travel far and fast, or exit the surface rapidly, may indicate a lower chance of settlement. An increase in time spent on a surface may increase the probability of being in contact with the surface when the sign stimulus to settle occurs.

The adhesive strategies of cyprids and development of barnacle-resistant marine coatings

Over the last decade, approaches to the development of surfaces that perturb settlement and/or adhesion by barnacles have diversified substantially. Although, previously, coatings research focussed almost exclusively on biocidal technologies and low modulus, low surface-free-energy 'fouling-release' materials, novel strategies to control surface colonisation are now receiving significant attention. It is timely, therefore, to review the current 'state of knowledge' regarding fouling-resistant surface characteristics and their mechanisms of action against settling larvae of barnacles. The role of the barnacle in marine fouling is discussed here in the context of its life cycle and the behavioural ecology of its cypris larva. The temporary and permanent adhesion mechanisms of cyprids are covered in detail and an overview of adult barnacle adhesion is presented. Recent legislation has directed academic research firmly towards environmentally inert marine coatings, so the actions of traditional biocides on barnacles are not described here. Instead, the discussion is restricted to those surface modifications that interfere with settlement-site selection and adhesion of barnacle cypris larvae; specifically, textural engineering of surfaces, development of inert 'non-fouling' surfaces and the use of enzymes in antifouling.

Smelly feet are not always a bad thing: the relationship between cyprid footprint protein and the barnacle settlement pheromone

A critical phase in the life cycle of sessile benthic marine invertebrates is locating a suitable substratum for settlement. For barnacles, it is the lecithotrophic cypris larva that makes this plankto-benthic transition. In exploring possible substrata for settlement, the cyprid leaves behind 'footprints' of a proteinaceous secretion that reportedly functions as a temporary adhesive, and also acts as a secondary cue in larval-larval interactions at settlement. Here, we show that two polyclonal antibodies raised against peptides localized at the N- and C-terminal regions of the adult settlement cue--the settlement-inducing protein complex (SIPC)--could both detect 'temporary adhesive' indicating that the SIPC is either a component of this secretion or that they are the same protein.

Crustacean peptide and peptide-like pheromones and kairomones

Crustacean peptide pheromones, kairomones, and substituted amino sugar kairomones are reviewed from a historical perspective. These crustacean information molecules are secondary functions of structural polymers. They are partial hydrolysis products, generated usually by the action of trypsin-like enzymes on proteins, and glycosidase enzymes on glycoproteins and proteoglycans. Structure-function studies based upon synthetic mimics of peptide information molecules show neutral amino acids with a basic carboxyl terminal are active in modifying physiological and or behavioral responses. Behaviorally active substituted amino sugar mimics are disaccharide hydrolysis products of heparin and chondroitin sulfate. Similar molecules are also used as information molecules by a variety of other marine organisms indicating they are a common biological theme.

Species specificity of barnacle settlement-inducing proteins

We previously isolated a larval settlement-inducing protein complex (SIPC) from adult extracts of the barnacle, Balanus amphitrite using a nitrocellulose membrane settlement assay. In the present study, we found that the extracts of other adult barnacles, Megabalanus rosa and Balanus eburneus, also induced the settlement of B. amphitrite cyprids although the inductive activity was slightly lower than that of conspecific extracts. Furthermore, we examined reactivity to anti-SIPC antibody in adult extracts from six species of Japanese barnacles other than B. amphitrite, brine shrimp and eight marine sessile organisms besides barnacles. The results showed that all barnacles examined contained SIPC-like proteins with slightly different molecular weight, while the other animals did not react to the antibody by immunoblot analysis. These findings suggest that species specificity in settlement-inducing proteins of barnacles is not so strict, but these proteins are characteristic to barnacle species.

Nature and perception of barnacle settlement pheromones

It is now almost 50 years since the gregarious settlement of barnacles and its chemical basis was first described. Although originally noted for Elminius modestus, mechanistic studies of gregariousness have focused on two species, Semibalanus balanoides and Balanus amphitrite. By virtue of its ease of study and its economic importance as a fouling organism, the latter species has assumed increasing importance in recent years. This paper will provide an overview of studies on settlement pheromones and their perception. An adult glycoprotein, arthropodin (now known as settlement-inducing protein complex or SIPC), was once thought to be the sole pheromone involved in the induction of cypris larval settlement. At least two other pheromones are now known to be involved, a waterborne cue originating from the adult and the cypris temporary adhesive. The latter is related, immunologically, to SIPC. In keeping with many other examples of chemical communication, the available evidence suggests that barnacle settlement induction involves receptor-ligand interactions and a signal transduction pathway(s) that translates into attachment and metamorphosis. Similar findings have been reported for some, but not all, marine invertebrate larvae examined thus far and the implications for antifoulant development are discussed.

Immunological studies on the settlement-inducing protein complex (SIPC) of the barnacle Balanus amphitrite and its possible involvement in larva-larva interactions

Immunological investigation has revealed that a settlement-inducing protein complex (SIPC), which induces cypris settlement of the barnacle Balanus amphitrite, is synthesized during larval development and accumulates in the cypris larva. We previously purified the SIPC from adult B. amphitrite, which was active when bound to a substratum. The SIPC is a glycoprotein of high molecular mass, consisting of three major subunits of 76, 88 and 98 kDa with lentil lectin (LCA)-binding sugar chains. In the present study, we prepared antiserum against each LCA-binding subunit of SIPC, and performed immunoblot analyses. Immunoblotting of adult extracts showed that anti-76-kDa antibody reacted only with the 76-kDa protein, whereas anti-88-kDa and anti-98-kDa antibodies reacted with both the 88-kDa and the 98-kDa proteins. Immunoblotting of larval extracts indicated that reactivity of the 76-kDa protein to anti-76-kDa antiserum increased during larval development and cyprid extracts reacted strongly. Moreover, by using immunostaining we found that the SIPC was contained in 'footprints' of cyprids, which have been shown to act as a settlement-inducing pheromone, and is secreted onto the antennular attachment discs. The results suggest that the SIPC (or SIPC-like proteins) is involved in both adult-larva and larva-larva interactions during settlement of the barnacle B. amphitrite.

On the structure of the antennular attachment organ of the cypris larva of Balanus balanoides (L.)

The third segment of the antennule of the cypris larva of Balanus balanoides is modified as an attachment organ with a disk by which the cyprid attaches to submerged surfaces. The attachment disk is covered with a felt of fine cuticular villi. Opening on to the disk are terminal branches of the cement duct, numerous glands and an array of sensory hairs. The sensory structures are arthropod scolopidia with the dendrites giving rise to cilia which, distally, change to distal sensory processes. It is suggested that the cuticular hairs situated in invaginations of the cuticle around the margin of the disk function as position receptors and that the two setae lying away from the cuticle of the segment are mechanoreceptors. Three of the scolopidia have structures suiting them for chemoreception; the distal sensory processes are exposed to the exterior at the tip of the hair. Two of these hairs are positioned at the margin and one at the centre of the disk. The fourth segment, which arises from the side of the attachment organ, is packed with sensory cell processes which are associated with setae arising at the distal end; its movements are controlled by a single muscle from the third segment. A suction mechanism of adhesion is precluded as there are no structures which could effect or release suction beneath the disk. The disk could act as an adhesive pad, with the cuticular villi increasing its surface area and the antennular glands possibly secreting a viscous substance. The presence of chemoreceptors on the attachment organ indicates that a chemosensory mechanism could operate during the gregarious behaviour of settling cyprids.

Studies on the larval structure and metamorphosis of Balanus balanoides (L.)

Balanus balanoides (L.) has seven planktonic larval stages. The first six are nauplius larvae while the seventh is the cypris larva. The cypris larva is specially adapted to locate a suitable place for settlement. The structure of the nauplius larva is basically similar to that of the nauplii of other crustacean groups. During successive nauplius stages, however, the simplicity of its anatomy is progressively obscured by the development of the cypris organ systems. All the organ systems do not differentiate simultaneously, but development is closely related to the time at which the organ must start to function. The three pairs of nauplius appendages, antennules, antennae and mandibles, are used in locomotion and the latter two pairs are also used in feeding. The six pairs of cypris thoracic swimming appendages, and the first and second maxillae with their associated ganglia and muscles, develop from groups of ectoteloblasts and mesoteloblasts in the ventral thoracic region of the nauplius. The compound eyes develop as outgrowths of the lateral lobes of the brain. The paired cement glands develop pre-orally. The end sacs of the adult maxillary glands develop as cavities in the somites of the second maxillary segment. The cypris antennules develop within the nauplius antennules but differentiation of their intrinsic musculature is delayed until after the nauplius-cypris moult. The various muscles of the cypris carapace are fully formed by the time of the nauplius-cypris moult. During, and after, the moult, a number of morphological and histological changes occur. The antennae and mandibles regress, the intrinsic musculature and cement ducts of the antennules complete their development. At the same time all the nauplius muscles and the antennal glands histolyse. Until these changes are completed the cypris larva is probably unable to settle, and thus to initiate the changes leading to the completion of metamorphosis. Rudimentary adult mandibles, and first and second maxillae are incorporated into the oral cone. After the moult the digestive region of the nauplius mid-gut epithelium and other epithelial cells are sloughed off into the gut lumen and digested together with the remains of the food ingested by the nauplius. The oesophagus and hind gut are now closed and the cypris larva does not feed. The adult digestive glands develop at the junction of the oesophagus and mid-gut. In the cypris the nauplius frontal filaments are associated with the compound eyes and connected to the brain via the optic ganglia. The median eye is apparently unchanged. Paired antennular ganglia are present. Those neurons, which innervated nauplius structures which have histolysed, also degenerate. The nauplius antennal glands degenerate at the nauplius-cypris moult; the maxillary glands are probably the functional organs of ionic regulation in the cypris as well as in the adult. The conspicuous multinucleate oil cells of the cypris are probably a food reserve. The paired masses of yellow cells in the carapace, originate in the antennae of the nauplius and migrate into the carapace after the moult. During the 24 h between settlement and the moult to the young adult, all the cypris muscles histolyse. The muscles break up spontaneously into short fragments which are then ingested by phagocytic haemocytes. There is widespread histolysis of neurons in the nervous system and further cells are sloughed from the gut epithelium. The adult mantle muscles, which are recognizable in the free swimming cypris larva, complete their differentiation, and in the few hours preceding the cypris-adult moult the adult thoracic muscles develop. The nervous system assumes its adult form and adult neurons differentiate from cells which had previously lain dormant in the nervous system. The compound eyes, frontal filaments and optic ganglia degenerate, but the median eye persists apparently unchanged. The yellow cells disperse, but their function is unknown. The cement glands persist in the adult, but the adult gland cells differentiate from cells aroung the collecting duct of the larval gland while the larval cement gland cells histolyse. The median eye persists, but in the newly moulted adult the three components separate giving rise to the three adult photoreceptors: a pair of pigmented ocelli and a median unpigmented photoreceptor. Shortly after the moult the young adult resumes feeding. This study has shown that metamorphosis in Balanus balanoides must be thought of in terms of the change from the nauplius through the cypris to the young adult and not just as the changes taking place between settlement and ecdysis to the young adult.