Paleoecology of Boring Barnacles

The morphology of acrothoracican boreholes primarily expressesa mechanical mode of boring. Paleozoic representatives raspedonly in the vertical plane, while Mesozoic forms developed anadditional horizontal rasp to carve out the cavity for the ovaries.Boring barnacles strongly prefer shells of live hosts to inorganicand dead substrates, and epibenthonic shells to other ones,but otherwise show little host specificity. Only a few speciesseem to have developed close commensal relationships with specifichosts, such as burrowing echinoids, nectonic belemnites, andhermit crabs.     

Barnacles and biofouling

Biofouling, the attachment and growth of organisms on submerged, man-made surfaces, has plagued ship operators for at least 2500 years. Accumulation of biofouling, including barnacles and other sessile marine invertebrates, increases the frictional resistance of ships' hulls, resulting in an increase in power and in fuel consumption required to make speed. Scientists and engineers recognized over 100 years ago that in order to solve the biofouling problem, a deeper understanding of the biology of the organisms involved, particularly with regard to larval settlement and metamorphosis and adhesives and adhesion, would be required. Barnacles have served as an important tool in pursuing this research. Over the past 20 years, the pace of these studies has accelerated, likely driven by the introduction of environmental regulations banning the most effective biofouling control products from the market. Research has largely focused on larval settlement and metamorphosis, the development of new biocides, and materials/surface science. Increased research has so far, however, failed to result in commercial applications. Two recent successes (medetomidine/Selektope?, surface-bound noradrenaline) build on our improving understanding of the role of the larval nervous system in mediating settlement and metamorphosis. New findings with regard to the curing of barnacle adhesives may pave the way to additional successes. Although the development of most current biofouling control technologies remains largely uninfluenced by basic research on, for example, the ability of settling larvae to perceive surface cues, or the nature of the interaction between organismal adhesives and the substrate, newly-developed materials can serve as useful probes to further our understanding of these processes.     

Convenient Assay for Settlement Inducing Substances of Barnacles

A convenient assay method for estimation of barnacle, Balanus amphitrite, settlement inductive activity was developed. To avoid the inductive effect by comrades and laborious observation requirements, cyprid larvae were put individually into wells of a 96-well plate. The settlement ratio from the experiment without any inducers was quite low; therefore this assay allowed easy estimation of settlement inductive activities. Some known inductive agents, such as serotonin and barnacle extracts, clearly showed inductive activities. This assay method is proven to be suitable for estimation of barnacle settlement-inducing activities of both water-soluble and -insoluble compounds. Received October 31, 1997; accepted July 10, 1998.     

Barnacles (Cirripedia: Thoracica) from the equatorial East Pacific

Previously unidentified barnacles (Cirripedia: Thoracica) that were collected during the ninth cruise of the R/V Akademik Mstislav Keldysh in the equatorial zone of the East Pacific Ocean from depths of 1422–1490 m are examined. The following species were found in two samples we studied: Amigdoscalpellum costellatum, A. elegans, Arcoscalpellum michelottianum, Annandaleum gruvelii gruvelii, Cristallinaverruca allisoni, and Metaverruca recta. These species are described, illustrated, and compared to the published data. This study extends the previously known areas of distribution of some species and adds further data on their morphology.     

The Phylogenetic Position of the Rhizocephala: Are They Truly Barnacles?

Incorporation of the Rhizocephala in the Cirripedia, reflecting the traditional view that these parasites evolved from a setose feeding barnacle, has recently been challenged in favour of rhizocephalans being the sister group to all other Thecostraca or a scenario where they evolved from a free-living, ‘precirripede’ ancestor. Adult morphology is useless in discussing the monophyly of the Cirripedia, since rhizocephalan adults are too reduced to furnish any phylogenetic evidence. But numerous, detailed similarities in nauplii and cyprids of the Thoracica, Acrothoracica and Rhizocephala as well as the ultrastructure of their sperm are synapomorphic relative to other Thecostraca and indicate that these three orders form a monophylum. There is evidence that the stylet in the rhizocephalan kentrogon is homologous to an element in the ancestral mouth field. If so, the Rhizocephala probably evolved before setose feeding was adopted, and constitute the sister group to the Acrothoracica and Thoracica. This conclusion is based on frail evidence so the term Cirripedia should be retained to comprise the Rhizocephala, Thoracica, and Acrothoracica. These three orders all possess remarkably similar cyprids, adapted to accomplish irreversible settlement by cement secretion and initiate metamorphosis, so their last common ancestor was most probably a permanently sessile organism.     

Biodiversity and Biogeography of Chthamalid Barnacles from the North-Eastern Pacific (Crustacea Cirripedia)

The biogeography and ecology of the species of Chthamalus present on the west coast of America are described, using data from 51 localities from Alaska to Panama, together with their zonation on the shore with respect to that of other barnacles. The species present were C. dalli, Pilsbry 1916, C. fissus, Darwin, 1854, C. anisopoma Pilsbry 1916 and four species in the C. panamensis complex. The latter are C. panamensis Pilsbry, 1916, C. hedgecocki, Pitombo & Burton, 2007, C. alani nom. nov. (formerly C. southwardorum Pitombo & Burton, 2007) and C. newmani sp. nov.). These four species were initially separated by enzyme electrophoresis. They could only be partially separated by DNA bar coding but may be separated using morphological characters.     

Scanning Electron Microscopy of Mouth Appendages in Six Species of Barnacles (Crustacea Cirripedia Thoracica)

The morphology and setation of mouth appendages (trophi) are investigated with scanning electron microscopy in the balanomorph barnacles Semibalanus balanoides, Balanus balanusand B. nubilusand in the pedunculate barnacles Pollicipes polymerus, P. cornucopiaand Lepas anatifera.It is difficult to uphold a clearcut distinction between denticles and setae and several types of setae also intergrade with each other. The trophi of Pollicipes polymerusand P. cornucopiahave the most ‘generalized’ morphology. The palps of Pollicipesand L. anatiferaare simpler than those in balanomorphs and carry a single type of seta. In L. anatiferathe mandibles and maxillules are adapted to a semi-predatory feeding habit by carrying large, pointed teeth, but this species lacks the foliate-serrate setae which populate the palps in the other species studied. Compared with Pollicipesand Lepas, the three balanomorphs have palps with a complex setation. The trophi in S. balanoidesdiffer from the two species of Balanusin numerous features of setation and denticulation, notably in having the palps populated by plumodenticulate setae homologous to purely denticulated types in Balanus.It is suggested that SEM studies of barnacle trophi will provide characters of use in estimating phylogeny.     

Larvae of Barnacles (Cirripedia: Thoracica) in the White Sea Plankton

The barnacle fauna of the White Sea is briefly described. The morphology of barnacle larvae in this water body is comparatively analyzed. The characters important for the larvae identification are given particular attention. A classification key for the naupliar and cyprid larvae of White Sea barnacles is proposed.     

Metamorphosis in Balanomorphan, Pedunculated, and Parasitic Barnacles: A Video-Based Analysis

Cypris metamorphosis was followed using video microscopy in four species of cirripeds representing the suspension-feeding pedunculated and sessile Thoracica and the parasitic Rhizocephala. Cirripede metamorphosis involves one or more highly complex molts that mark the change from a free cypris larva to an attached suspension feeder (Thoracica) or an endoparasite (Rhizocephala). The cyprids and juveniles are so different in morphology that they are functionally incompatible. The drastic reorganization of the body implicated in the process can therefore only commence after the cyprid has irreversibly cemented itself to a substratum. In both Megabalanus rosa and Lepas, the settled cyprid first passes through a quiescent period of tissue reorganization, in which the body is raised into a position vertical to the substratum. In Lepas, this is followed by extension of the peduncle. In both Lepas and M. rosa, the juvenile must free itself from the cypris cuticle by an active process before it can extend the cirri for suspension feeding. In M. rosa, the juvenile performs intensely pulsating movements that result in shedding of the cypris carapace ～8?h after settlement. Lepas sp. sheds the cypris cuticle ～2 days after settlement due to contractile movements of the peduncle. In Lepas anserifera, the juvenile actively breaks through the cypris carapace, which can thereafter remain for several days without impeding cirral feeding. Formation of the shell plates begins after 1-2 days under the cyprid carapace in Lepas. In M. rosa, the free juvenile retains its very thin cuticle and flexible shape for some time, and shell plates do not appear until sometime after shedding of the cypris cuticles. In Sacculina carcini, the cypris settles at the base of a seta on the host crab and remains quiescent and aligned at an angle of ～60° to the crab's cuticle. The metamorphosis involves two molts, resulting in the formation of an elongated kentrogon stage with a hollow injection stylet. Due to the orientation of the cyprid, the stylet points directly towards the base of the crab's seta. Approximately 60?h after settlement the stylet penetrates down one of the cyprid antennules and into the crab. Almost immediately afterwards the unsegmented vermigon stage, preformed in the kentrogon, passes down through the hollow stylet and into the crab's hemocoel in a process lasting only 30?s. In S. carcini, the carapace can remain around the metamorphosing individual without impeding the process.     

The Impact of Desiccation on the Adhesion of Barnacles Attached to Non-stick Coatings

Fouling-release coatings prevent fouling of ships' hulls through hydrodynamic forces generated as the ship moves through the water. The effectiveness of such coatings may be evaluated by measuring the adhesion strength of settled organisms, e.g. barnacles. The influence of desiccation of the barnacle adhesive on such measurements was investigated. Shear forces required to remove barnacles of the genus Balanus increased during the course of desiccation up to the point when the barnacles suddenly self-detached. The increase was thought to be due to the rising cohesive strength of the adhesive. Growing tensile forces within the weakly cross-linked adhesive, however, are suggested to have led to self-detachment. The shear forces required to remove barnacles of the genus Elminius were generally low and did not differ significantly during the course of desiccation. The different results may be attributed to specific base morphologies. It was concluded that measuring the adhesion strength of members of the Balanidae on non-stick surfaces in air could produce flawed results due to the influence of desiccation of the barnacle adhesive. The investigations have also provided new insights into the characteristics of barnacle adhesive.     

Speciation Versus Phenotypic Plasticity in Coral Inhabiting Barnacles: Darwin's Observations in an Ecological Context

Speciation and phenotypic plasticity are two extreme strategic modes enabling a given taxon to populate a broad ecological niche. One of the organismal models which stimulated Darwin's ideas on speciation was the Cirripedia (barnacles), to which he dedicated a large monograph. In several cases, including the coral-inhabiting barnacle genera Savignium and Cantellius (formerly Pyrgoma and Creusia, respectively), Darwin assigned barnacle specimens to morphological ``varieties' (as opposed to species) within a genus. Despite having been the subject of taxonomic investigations and revisions ever since, the significance of these varieties has never been examined with respect to host-associated speciation processes. Here we provide evidence from molecular (12S mt rDNA sequences) and micromorphological (SEM) studies, suggesting that these closely related barnacle genera utilize opposite strategies for populating a suite of live-coral substrates. Cantellius demonstrates a relatively low genetic variability, despite inhabiting a wide range of corals. The species C. pallidus alone was found on three coral families, belonging to distinct higher-order classification units. In contrast, Savignium barnacles exhibit large between- and within-species variations with respect to both micromorphology and DNA sequences, with S. dentatum ``varieties' clustering phylogenetically according to their coral host species (all of which are members of a single family). Thus, whereas Savignium seems to have undergone intense host-associated speciation over a relatively narrow taxonomic range of hosts, Cantellius shows phenotypic plasticity over a much larger range. This dichotomy correlates with differences in life-history parameters between these barnacle taxa, including host-infestation characteristics, reproductive strategies, and larval trophic type. Received: 18 January 1999 / Accepted: 9 May 1999     

Barnacles vs bullies: modelling biocontrol of the invasive European green crab using a castrating barnacle parasite

Invasive species raise concern around the globe, and much empirical and theoretical research effort has been devoted to their management. Integrodifference equations are theoretical tools that have been used to understand the spatiotemporal process of a species invasion, with the potential to yield insight into the possible biological control measures. We develop a system of integrodifference equations to explore the potential release of a castrating barnacle parasite Sacculina carcini to control spread and abundance of an invasive species, Carcinus maenas, the European green crab. We find that the parasite does not completely eradicate the green crab population, but has the potential to reduce its density. Our model suggests that the crab population is likely to outrun the spread of the parasite, causing two waves of invasion travelling at different speeds. By performing a sensitivity analysis, we investigate the effects of the demographic parameters on the speed of invasion. To conclude, we discuss the predicted outcomes for the European green crab, and other non-target hosts, of using the castrating barnacle as a biocontrol agent.     

Terpenes from the Red Alga <Emphasis Type="Italic">Sphaerococcus coronopifolius</Emphasis> Inhibit the Settlement of Barnacles

In this study, we screened eight terpenes isolated from the organic extract of Sphaerococcus coronopifolius for their antifouling activity in order to find possible new sources of non-toxic or less toxic bioactive antifoulants. The anti-settlement activity (EC₅₀) and the degree of toxicity (LC₅₀) of S. coronopifolius metabolites was evaluated using larvae of the cirriped crustacean Amphibalanus (Balanus) amphitrite (cyprids and nauplii) as model organism. For five of eight tested metabolites EC₅₀ was lower than 5 mg/L. The most promising results were observed for bromosphaerol (3), which expressed an EC₅₀ value of 0.23 mg/L, in combination with low toxicity levels (LC₅₀ > 100 mg/L). The therapeutic ratio—an index used to estimate whether settlement inhibition is due to toxicity or other mechanisms—is also calculated and discussed.     

Boschmaella japonica,New Species,a Parasite on the Barnacles Chthamalus challengeri and Balanus amphitrite amphitrite from Japan (Crustacea: Cirripedia: Rhizocephala: Chthamalophilidae)

Abstract A new rhizocephalan parasite which infests the barnacles Chthamalus challengeri and Balanus amphitrite amphitrite is described. It is known only from the type locality, Aburatsubo, Kanagawa Prefecture, Japan. Its position in the family Chthamalophilidae is assured by the cyprids lacking a thorax, by the position of the mesenteric canal opposite to the stalk, and by its host being a balanomorph barnacle. Among the three previously described species of the Chthamalophilidae, the new species most closely resembles Boschmaella balani, but it differs in details of the internal root system and in the externa being found both on the host body and on the inner mantle. About two-thirds of the infested hosts carry more than one externa.