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Background: Large numbers of exotic marine species have been introduced worldwide. Monitoring of introduced species is important to reveal mechanisms underlying their establishment and expansion. Balanus glandula is a common intertidal barnacle native to the northeastern Pacific. However, this species has been introduced to Japan, South America, South Africa, and Europe. While a latitudinal genetic cline is well known in its native range, it is unclear whether such a genetic cline occurs in introduced areas. Twenty years have passed since it was first identified in Japan and its distribution now ranges from temperate to subarctic regions. Methods: In the present study, we examined genotypes of cytochrome oxidase subunit I (COI) of mitochondrial (mt)-DNA and elongation factor 1a (EF1) across the distribution of B. glandula in Japan at high and mid intertidal zones. Results: At all sampling sites, native northern genotypes are abundant and I did not detect significant effects of latitude, tide levels, or their interaction on genotypic frequencies. Further, I did not detect any change of genotype composition between data collected during a study in 2004 and samples in the present study collected in 2019. Data from the present study offer an important baseline for future monitoring of this species and supply valuable insights into the mechanisms of establishment and expansion of introduced marine species generally. [ABSTRACT FROM AUTHOR]

Invasive species often exhibit disproportionately strong negative effects in their introduced range compared to their native range, and much research has been devoted to understanding the role of shared evolutionary history, or lack thereof, in driving these differences. Less studied is whether introduced species, particularly those that are important as facilitators in their native range, have persistent positive effects in their invaded range despite a lack of a shared evolutionary history with the invaded community. Here, we manipulated the density of a habitat‐forming facilitator, the high intertidal acorn barnacle Balanus glandula, factorially with herbivore density in its native range (Bluestone Point, British Columbia, Canada) and invaded range (Punta Ameghino, Chubut Province, Argentina) to determine how this facilitator differentially affects associated species at these two locations. Given that high intertidal species at Punta Ameghino (PA) are evolutionarily naïve to barnacles, we predicted that the positive effects of B. glandula at PA would be absent or weak compared to those at Bluestone Point (BP). However, we found that B. glandula had an equally positive effect on herbivore biomass at PA compared to BP, possibly because the moisture‐retaining properties of barnacle bed habitats are particularly important in seasonally dry Patagonia. Barnacle presence indirectly decreased ephemeral algal cover at BP by increasing grazer pressure, but barnacles instead facilitated ephemeral algae at PA. In contrast, B. glandula increased perennial algal cover at BP, but generally decreased perennial algal cover at PA, likely due to differences in dominant algal morphology. Though our experiment was limited to one location on each continent, our results suggest that shared evolutionary history may not be a prerequisite for strong facilitation to occur, but rather that the nature and strength of novel species interactions are determined by the traits of associated species and the environment in which they occur. [ABSTRACT FROM AUTHOR]

Aim: As within‐species genomic data have been shown useful in interpreting broader biogeographic trends, we analysed the mode of population genomic isolation involved in a well‐studied intertidal genomic cline to better understand the mechanisms maintaining it. These results were interpreted in the context of spatial variation in habitat use and availability as well as likely fitness consequences for hybridization between the two lineages. Location: Pacific coast of North America. Taxon: Arthropods (Class Maxillopoda, Order Sessilia, Family Balanidae; Balanus glandula). Methods: Genotype‐by‐sequencing approaches were used to generate single‐nucleotide polymorphism markers across sites sampled between southern Alaska and Southern California. Inference using standard population genomic methods, including analysis of population structure, inbreeding and linkage disequilibrium, was used to identify the steepest transitions across the largest number of loci examined. These data were put in the context of observed population density and habitat availability. Results: We show that the majority of markers analysed show strong clinal transitions in a very narrow portion of the California coast. Patterns of linkage disequilibrium among markers, along with prior evidence of variation in reproductive potential by latitude and by mitochondrial lineage, suggest some reproductive isolation among the northern and southern lineages of B. glandula that are concordant with the drop in population density and habitat availability in central California. Main Conclusions: A significant clinal transition in genomic diversity is stronger and more localized than previously recognized and exhibits statistical patterns suggesting that the lineages are reproductively and phenotypically distinct in ways that may be ecologically important. As this species has been used to infer process in coastal biogeography, further study of concordant patterns will be important for advancing our understanding of this region. [ABSTRACT FROM AUTHOR]

Sensory systems provide critical filters that enable organisms to detect and recognize valuable resources. Trophic cascades, structuring populations and communities, are determined to a large degree by trait-mediated interactions that rely on sensory inputs. Certain molecules serve as chemosensory stimuli and play keystone roles in determining outcomes of predator-prey dynamics at multiple trophic levels. Here, a surface-adsorbed glycoprotein signal molecule, MULTIFUNCin, is fully identified and its role in waveswept rocky intertidal community dynamics investigated. Barnacles (Balanus glandula), are constrained to produce MULTIFUNCin for cuticle/shell formation. This compound evoked settlement by conspecifics larvae in field assays, and thus, operates as seminal cue for recruitment. Moreover, the same substances triggered predation by a numerically dominant whelk species (Acanthinucella spirata) on barnacle juveniles and adults in lab and field experiments. This glycoprotein, therefore, balances simultaneous demographic processes that enhance, and diminish, barnacle populations. As dominant competitors for space, the relative equilibrium between barnacle recruitment and predation mortality has strong, cascading direct and indirect effects on community dynamics. Hence, MULTIFUNCin plays a keystone role within rocky intertidal habitats.

Introduced species are a major threat to coastal ecosystems worldwide. Thus, understanding biotic resistance (i.e. the ability of native species to limit introduced species) is a central goal of invasion biology. This paper examines mechanisms underlying biotic resistance. Consumption can limit introduced prey provided that native predators prefer such prey. Furthermore, predator nonconsumptive effects (NCEs), mediated through predator-released cues perceived by prey, can limit prey recruitment, a key demographic process for prey populations. However, information on predator NCEs is largely absent in the context of recruitment in introduced prey. Working on the Pacific coast of Hokkaido (Japan), we addressed this knowledge gap using native predatory dogwhelks (Nucella lima) that prey on native barnacles (Chthamalus dalli) and introduced barnacles (Balanus glandula). We experimentally examined dogwhelk preferences for barnacles in the laboratory and dogwhelk NCEs on barnacle recruitment in the field. We found that N. lima preferred B. glandula over C. dalli, likely as B. glandula prey is more profitable, as suggested by previous findings in congeneric dogwhelks. Moreover, we found that N. lima NCEs limited recruit density in C. dalli and B. glandula, likely as barnacle larvae moved away from dogwhelk cues to reduce future predation risk. Our study suggests that predator prey preferences and predator nonconsumptive limitation of prey recruitment are two mechanisms that can contribute to predator-driven biotic resistance against introduced prey. [ABSTRACT FROM AUTHOR]

The barnacle Balanus glandula is a broadly distributed species in the temperate northeastern Pacific that is notable for a robust genetic cline between about 36° and 40° N latitude. Prior work established the evolutionary origins of this pattern and proposed that it is maintained by environmental selection. In recent years, "climate velocity" studies in marine habitats have shown dramatic distributional shifts for many species as they track their preferred temperature range in a warming ocean. We re-sampled B. glandula across its entire geographic range to determine whether there has been any shift in this genetic distribution, a development signaling that temperature or other climate factors are maintaining this genetic cline. Additionally, we asked whether the spatially distributed mitochondrial lineages also vary in reproductive output with latitude, using location as a proxy for temperature and other coastal environmental factors. Here we show that although the distribution of the genetic cline has not appreciably changed, there is a notable association of decreased reproductive output at lower latitudes of the distribution in the "northern" lineage of B. glandula. [ABSTRACT FROM AUTHOR]

Many crustacean swimming appendages carry arrays of plumose setae—exoskeletal, feather-like structures of long bristles (setae) with short branches (setules) distributed along two sides. Although closely spaced, setae are not physically interconnected. Setal arrays function during swimming as drag-based leaky paddles that push the organism through water. Barnacle cyprids, the final, non-feeding larval stage, swim with six pairs of legs (thoracopods) that open and close setal arrays in alternating high-drag power strokes and low-drag recovery strokes. While studying cyprid swimming, we found that their thoracopods contained setae permanently cross-linked by fused setules. These cuticular connections would seem highly unlikely because setae are individually produced exoskeletal secretions, and the connections imply unknown processes for the production or modification of crustacean setae. We describe the morphology and function of plumose setae on cyprids of Balanus glandula and other species across the clade Cirripedia. Setules from adjacent plumose setae are seamlessly joined at their tips and occur in three distinct linkage patterns. Thoracopods lack muscles to open and close the array; interconnected setae are instead pulled apart, producing a paddle-like fan with high drag when appendages spread laterally during power strokes. Setules are spring-like, passively closing setae into tight bundles with low drag during recovery strokes. The linked setules occur in the three main clades of the Cirripedia. This cuticular arrangement is effective in swimming, may eliminate the need for muscles to close the setal array, and may represent a unique swimming structure within the Crustacea. [ABSTRACT FROM AUTHOR]

To elucidate how the population dynamics of the acorn barnacle Balanus glandula transitioned after its invasion in 2000 along the Pacific coast of Japan, a population census was conducted from 2004 to 2014 at five shores along 49 km of coastline 144–193 km east outside of the invasion front. Survey areas at each shore consisted of five paired plots (cleared recruitment plots and control plots). Larval recruitment was first detected in 2004 but benthic individuals were not detected until 2 years later. The abundance and occurrence of B. glandula increased until around 2010; abundance then decreased but occurrence remained high (70%) until 2014, suggesting that the metapopulation of this barnacle approached a maximum around 2011. From 2011, the population dynamics of B. glandula changed considerably at two contrasting spatial scales: at a regional scale, the dependency of the number of larvae on stock size decreased, whereas at a local scale, the relative contribution of larval supply as a determinant of local population dynamics decreased. These findings suggest that the major driving force of population dynamics of the introduced barnacle changed in just a few years after invasion; therefore, population census data from just after an invasion, including larval recruitment monitoring just outside the invasion front, is essential to understanding invasion dynamics by sessile marine organisms.

The South African coastline has been invaded by numerous alien species. Rare pre-invasion (1980) and post-invasion datasets (2001 and 2012) exist for Marcus Island, a small land-tied island in Saldanha Bay, South Africa. These snapshot datasets of the island’s intertidal invertebrate community were complemented with monitoring across seasons, from 2014 to 2016. Invertebrate communities were compared among the summers of 1980, 2001, 2012, 2014, 2015 and 2016 to assess interannual differences, while invertebrates and algae were monitored quarter-annually to assess seasonal changes. In addition, the population dynamics of the alien mussel Mytilus galloprovincialis were monitored. Differences in invertebrate communities between consecutive summers were significant but much smaller than changes induced by the arrival of alien species. Invertebrate and seaweed communities differed among years and shore zones but not among seasons, whereas species diversity differed among years, seasons and shore zones, with zones having the strongest influence. The invasion by M. galloprovincialis, and ensuing spatial and temporal variability in its recruitment, emerged as the most important factor influencing community composition, overshadowing interannual and seasonal changes. This work highlights that the impacts of alien species can be distinguished from natural variability by combining long-term monitoring with surveys at finer temporal scales. This is an important step in extending our understanding of the impacts of marine alien species. [ABSTRACT FROM AUTHOR]

Suspension feeders use a wide range of appendages to capture particles from the surrounding fluid. Their functioning, either as a paddle or a sieve, depends on the leakiness, or amount of fluid that passes through the gaps between the appendages. Balanus glandula is the most common species of barnacle distributed along the Pacific coast of North America. It shows a strong phenotypic response to water flow velocity. Individuals from exposed, high flow sites have short and robust cirral filters, whereas those from sheltered, low velocity sites have long, spindly appendages. Computational fluid dynamics (CFD) simulations of these two ecophenotypes were done using a finite volume method. Leakiness was determined by simulating flow velocity fields at increasing Reynolds numbers, results that have been unattainable at higher velocities by observation. CFD also allowed us to characterize flow in hard to see regions of the feeding legs (rami). Laser-illumination experiments were performed at low to medium flow velocities in a flume tank and corroborated results from CFD. Barnacle filters from a sheltered site become completely leaky at Re = 2.24 ( 0.16 m / s ) , well above the maximum habitat velocity, suggesting that this ecophenotype is not mechanically optimized for feeding. Barnacles from exposed environments become fully leaky within the range of habitat velocities Re = 3.50 ( 0.18 m / s ) . Our CFD results revealed that the drag force on exposed barnacles feeding appendages are the same as the sheltered barnacles feeding appendages despite their shape difference and spacing ratio. [ABSTRACT FROM AUTHOR]

During recent surveys of hard substrata biofouling communities in Belgian marine waters we discovered specimens of the invasive barnacle Balanus glandula. This species is new to the European marine fauna. The species was first encountered in July 2015 in a biofouling community on RV Belgica. In October 2016, the species proved to be common on navigational buoys in Belgian coastal waters and after a dedicated search we discovered the species on many groynes all along the Belgian coast and in the harbour of Zeebrugge. We identified the species both morphologically and genetically. We found two generations indicating that B. glandula had settled in 2015 (possibly the first year of its presence) and also in 2016. We provide identification characters to distinguish B. glandula from other, similar looking, Western European intertidal barnacles. The distribution of B. glandula was originally limited to the Pacific coast of North America. In the past half century B. glandula successfully invaded subsequently the coasts of Argentina, Japan and South Africa. Given its invasion history elsewhere, we forecast that B. glandula is on the brink of invading other European shores. [ABSTRACT FROM AUTHOR]

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The contribution of energy limitation to patterns of intertidal zonation and vertical range limits is not well understood. Higher vertical positions on an intertidal shore are typically associated with greater temperature and desiccation stress during emersion; yet, organisms at higher shore heights also experience reduced feeding time and thus also face greater energy limitation than their lower shore counterparts. Disentangling the roles of abiotic stress and food limitation is critical to accurately predicting intertidal species' responses to climate change. This experiment manipulated food supply and shore height for the intertidal barnacle Balanus glandula (Darwin 1854). Adults were maintained in the field for 39 days at one of four shore heights spanning the species' upper vertical range limit, with or without supplemental feeding during high tides. Higher shore animals showed significantly lower growth and higher mortality relative to those lower on the shore. Across all shore heights, fed animals had significantly higher overall growth (20–27% greater final body mass), but not survival, than animals in the control treatments. No significant interactions between height and feeding treatment were detected, although the benefits of supplemental feeding tended to be smaller at higher shore heights. Our results suggest that food limitation occurs across a large portion of B. glandula 's vertical range and that it can influence the success of barnacles at and above the current upper vertical limit. As such, energy limitation may play an important role in the vertical limits of many high intertidal species, and in distributional limits more broadly. [ABSTRACT FROM AUTHOR]

Many invertebrate species use the microhabitats generated by barnacles to settle and to avoid predation and desiccation. In Argentina, the acorn barnacle Balanus glandula not only colonizes rocky shores but has also successfully invaded soft bottom salt marshes, where it form large three-dimensional structures that facilitate the presence of other invertebrates, thus affecting the whole species assemblage. Artificial barnacles were deployed on a Patagonian salt marsh to reproduce the physical structure of natural aggregates. The experiment included natural and material controls and two levels of structural complexity that represent the variety of aggregates found in nature: (i) aggregates with internal empty spaces and galleries among barnacles and (ii) aggregates without spaces and galleries. After nine months, the macroinvertebrate assemblages were compared between treatments. The results showed that the composition of the assemblage differed significantly between artificial treatments and control plots. However, there was no effect of the mimic barnacles on macroinvertebrate richness and diversity. In this way, our results suggest that the physical structure of B. glandula could modify the composition of macroinvertebrate assemblages. Besides, B. glandula recruits were registered on the mimics highlighting the importance that the physical structure supplied by this species could have on its own persistence within invaded soft bottom salt marshes. [ABSTRACT FROM AUTHOR]

Species distribution models typically use correlative approaches that characterize the species-environment relationship using occurrence or abundance data for a single species. However, species distributions are determined by both abiotic conditions and biotic interactions with other species in the community. Therefore, climate change is expected to impact species through direct effects on their physiology and indirect effects propagated through their resources, predators, competitors, or mutualists. Furthermore, the sign and strength of species interactions can change according to abiotic conditions, resulting in context-dependent species interactions that may change across space or with climate change. Here, we incorporated the context dependency of species interactions into a dynamic species distribution model. We developed a multi-species model that uses a time-series of observational survey data to evaluate how abiotic conditions and species interactions affect the dynamics of three rocky intertidal species. The model further distinguishes between the direct effects of abiotic conditions on abundance and the indirect effects propagated through interactions with other species. We apply the model to keystone predation by the sea star Pisaster ochraceus on the mussel Mytilus californianus and the barnacle Balanus glandula in the rocky intertidal zone of the Pacific coast, USA. Our method indicated that biotic interactions between P. ochraceus and B. glandula affected B. glandula dynamics across >1000 km of coastline. Consistent with patterns from keystone predation, the growth rate of B. glandula varied according to the abundance of P. ochraceus in the previous year. The data and the model did not indicate that the strength of keystone predation by P. ochraceus varied with a mean annual upwelling index. Balanus glandula cover increased following years with high phytoplankton abundance measured as mean annual chlorophyll-a. M. californianus exhibited the same pattern to a lesser degree, although this pattern was not significant. This work bridges the disciplines of biogeography and community ecology to develop tools to better understand the direct and indirect effects of abiotic conditions on ecological communities. [ABSTRACT FROM AUTHOR]

As invasions become increasingly prevalent, it is important to understand how spread may be moderated by environmental conditions. This study considered the effect of location and changing substratum temperature on the early life-history processes of the alien barnacleBalanus glandulaand its native comparator,Chthamalus dentatus, along the South African coast. Using settlement plates of different colours, temperature was manipulated to assess settlement, mortality, recruitment and growth of the two species. These variables were tracked over 10 weeks using repeat photography. Unexpectedly, there was no evidence of an effect of temperature on early life-history processes of either species. Settlement by the two barnacles was spatially segregated, withB. glandulaoccurring only on the West Coast where it is the dominant intertidal barnacle, whileC. dentatussettled only on the South Coast, which has only recently been invaded by the alien. Despite this, it was notable that the relative settlement ofB. glandulaon rock was higher than that ofC. dentatus. However, the lack of mortality of the native resulted in comparable levels of recruitment among the species. Nonetheless, the propensity ofB. glandulato settle sporadically, coupled with fast growth, suggests that the invader may still possess the ability to become dominant along the newly invaded South Coast. This study highlights that measurements of early life-history parameters may not adequately predict the future range and impacts of alien species unless interpreted within the broader context of the nature of the recipient region and species-specific traits of the invader. [ABSTRACT FROM AUTHOR]

The barnacle, Balanus glandula has recently invaded along the Pacific coast of eastern Hokkaido, Japan. To evaluate the direct and indirect effects of endemic seaweeds, barnacles, and invertebrate predators on the abundance of B. glandula on the rocky intertidal coast of eastern Hokkaido, we conducted a field experiment from June 2011 to October 2012 in which we manipulated the presence or absence of these factors. Seaweeds showed no significant effect on the abundance of B. glandula. The endemic barnacle Chthamalus dalli and the invertebrate predator Nucella lima reduced the abundance of B. glandula. However, the simultaneous influence of N. lima and C. dalli was compensative rather than additive, probably due to keystone predation. These findings suggest that competition by the endemic barnacle C. dalli and predation by the invertebrate predator N. lima decreased the abundance of B. glandula, but that N. lima predation on C. dalli weakened the negative influence of C. dalli on B. glandula. The implications of these findings are twofold: the endemic competitor and invertebrate predator may have played important roles in decreasing the abundance of B. glandula in natural habitats, and conservation of endemic invertebrate predators may be crucial to impede the establishment and survival of introduced barnacles in rocky intertidal habitats. [ABSTRACT FROM AUTHOR]

If the external surfaces of epibionts are more suitable to other fouling species than those of their basibionts, a ‘fouling cascade’ might occur where epibionts facilitate secondary colonization by other epibionts. Here we evaluate whether the presence of epibiotic barnalces ( Balanus glandula ) influences the probability of mussel ( Brachidontes rodriguezii ) fouling by ephemeral red algae ( Porphyra sp.) in a Southwestern Atlantic rocky shore. Mussels with barnacle epibionts showed a higher prevalence of Porphyra sp. fouling (32–40% depending on sampling date) than mussels without them (3–7%). Two lines of evidence indicate that barnacles facilitate Porphyra sp. fouling. First, most Porphyra sp. thalli in mussels with barnacle epibionts were attached to barnacle shells (75–92% of cases). Secondly, Porphyra sp. associated with mussels with barnacle epibionts in a proportion that significantly exceeded that expected under random co-occurrence. These results suggest the occurrence of a fouling cascade where barnacle epibiosis on mussels facilitates subsequent algal fouling. Recognizing the occurrence of such fouling cascades is important because they might explain the non-random aggregation of multiple epibiotic species onto a proportionally few individuals of the host species. [ABSTRACT FROM AUTHOR]

The intertidal barnacle, Balanus glandula (Darwin), has invaded the South African coast within the past few decades. This species is currently the dominant barnacle on the cool and productive West Coast and has recently spread east past the biogeographic break of Cape Point. To understand if this invader is likely to establish dominance in these warmer, less productive waters, the effect of water temperature and food availability on the relative food resource use and feeding behaviour of B. glandula was investigated in comparison to the native barnacle, Notomegabalanus algicola (Pilsbry). To mimic conditions along the two coasts, barnacles were fed either a high (32 × 10 6 algal cells·ml − 1 ) or low (1 × 10 6 algal cells·ml − 1 ) algal concentration, representing the high and low primary productivity of the coasts respectively, at 13 and 20 °C. After an hour of filtration, the remaining cells were quantified using flow cytometry. To further resolve differences in feeding among species, video footage was used to quantify feeding behaviour. Notably, both water temperature and food concentration influenced barnacle filtration. However, regardless of thermal and productivity profiles, B. glandula demonstrated higher resource use than N. algicola . Unexpectedly, B. glandula exhibited highest filtration under conditions representative of the South Coast, not under cooler conditions that are typical of its native range and its initial invaded range along South African West Coast. Under these warmer, less productive conditions, B. glandula showed faster cirral beat rates than the native barnacle, although no differences in the number of feeding barnacles or the time spent feeding were recorded. Results suggest that (1) B. glandula displays heightened food resource use when compared to N. algicola regardless of water temperature or food concentration, (2) this likely reflects different feeding behaviours of the two species, and (3) feeding by B. glandula is enhanced under warmer water conditions. This work implies that the invasive barnacle may hold an advantage under South Coast conditions that could facilitate its spread in this newly invaded region. [ABSTRACT FROM AUTHOR]

Invasive species threaten native ecosystems worldwide. However, these species can interact positively with local communities, increasing their richness, or the abundance of some species. Many invasive species are capable of influencing the habitat itself, by ameliorating physical stress and facilitating the colonization and survival of other organisms. Barnacles are common engineer species that can change the physical structure of the environment, its complexity, and heterogeneity through their own structure. Balanus glandula is a native barnacle of the rocky shores of the west coast of North America. In Argentina, this invasive species not only colonizes rocky shores but it also has successfully colonized soft-bottom salt marshes, where hard substrata are a limiting resource. In these environments, barnacles form three-dimensional structures that increase the structural complexity of the invaded salt marshes. In this work, we compared the composition, density, richness, and diversity of the macroinvertebrate assemblages associated with habitats of different structural complexity in two Patagonian salt marshes where B. glandula is well established. Our results showed differences in the relative distribution and abundances of the invertebrate species between habitats of different complexities. Furthermore, the response of the communities to the changes in the structural complexity generated by B. glandula was different in the two marshes studied. This highlights the fact that B. glandula facilitates other invertebrates and affect community structure, mainly where the settlement substrata ( Spartina vs. mussels) are not functionally similar to the barnacle. Thus, our work shows that the rocky shore B. glandula is currently a critical structuring component of the native invertebrate community of soft-bottom environments where this species was introduced along the coast of southern South America. [ABSTRACT FROM AUTHOR]

Worldwide, marine rocky shores are being modified by alien species, but their successive impacts are rarely recorded. We documented sequential invasions of Marcus Island on the west coast of South Africa by comparing communities from 1980 (pre-invasion), 2001 (after invasion by the mussel Mytilus galloprovincialis) and 2012 (following invasions by another mussel, Semimytilus algosus, and the barnacle Balanus glandula). Their influence on habitat complexity was measured with a novel technique enabling retrospective calculation of historical complexity. In 1980, habitat complexity, invertebrate abundance and species richness decreased from the low-shore to the high-shore, but homogenised in 2001 after M. galloprovincialis elevated habitat complexity across most of the shore. In 2012, these variables returned to pre-invasion patterns, after M. galloprovincialis declined in the high-shore and was replaced there by B. glandula. With the first mussel invasion, several indigenous species extended up the intertidal, but retreated once M. galloprovincialis receded. Community composition differed significantly among nearly all years and zones, irrespective of whether the alien species were included in the analyses or not. Some once-dominant native species were negatively affected by the invasions: one indigenous mussel, Choromytilus meridionalis, disappeared by 2012, and another, Aulacomya atra, declined. The abundance of recruits of the limpet Scutellastra granularis rose and fell with the arrival and recession of M. galloprovincialis, but adults were adversely affected. Changes to habitat complexity induced by sequential invasions supported hypothesised changes in invertebrate abundance and species richness, but could not alone predict changes in community composition, which were also influenced by zonation. [ABSTRACT FROM AUTHOR]

Repeat photography was used to illustrate long-term changes occurring in coastal habitats in the Western Cape, South Africa. Historic images were sourced from books and theses, the public and subject specialists, and repeat photographs were then taken from the same perspectives. Visible changes could be categorised into four types: (1) changes in species’ ranges; (2) biological invasions; (3) sea level changes; and (4) direct engineering impacts. In terms of range changes, the images depict a progressive easterly spread of the cold-water kelpEcklonia maximaand parallel easterly contraction of the warmer-water musselPerna perna, both evidence for declining water temperatures along the South-West Coast. Since c. 1980 most shores have also become conspicuously invaded by the alien Mediterranean musselMytilus galloprovincialis, while those on the West Coast have also been visibly invaded by the more-recently introduced Pacific barnacleBalanus glandula. No changes in vertical zonation due to changing sea levels could be detected, despite suitable images being available. Construction along the shore has radically altered the appearance of the shoreline in urban areas. Repeat photography thus proved a useful tool for both detecting and dramatically illustrating historic changes over the past century. These changes have altered substantially both the appearance and ecological attributes of many rocky shores in this region. [ABSTRACT FROM AUTHOR]

Background: Large numbers of exotic marine species have been introduced worldwide. Monitoring of introduced species is important to reveal mechanisms underlying their establishment and expansion. Balanus glandula is a common intertidal barnacle native to the northeastern Pacific. However, this species has been introduced to Japan, South America, South Africa, and Europe. While a latitudinal genetic cline is well known in its native range, it is unclear whether such a genetic cline occurs in introduced areas. Twenty years have passed since it was first identified in Japan and its distribution now ranges from temperate to subarctic regions., Methods: In the present study, we examined genotypes of cytochrome oxidase subunit I (COI) of mitochondrial (mt)-DNA and elongation factor 1a (EF1) across the distribution of B. glandula in Japan at high and mid intertidal zones., Results: At all sampling sites, native northern genotypes are abundant and I did not detect significant effects of latitude, tide levels, or their interaction on genotypic frequencies. Further, I did not detect any change of genotype composition between data collected during a study in 2004 and samples in the present study collected in 2019. Data from the present study offer an important baseline for future monitoring of this species and supply valuable insights into the mechanisms of establishment and expansion of introduced marine species generally., Competing Interests: The authors declare that they have no competing interests., (© 2022 Yorisue.)

Abstract: The positive impact that native species have on the survival, persistence and/or range-expansion of invasive species, is receiving increasing attention from ecologists and land managers trying to better understand and predict future invasions worldwide. Ecosystem engineers are among the best-known model organisms for such studies. The austral cordgrass Spartina densiflora is an ecosystem engineer native to South America coast, where it colonizes rocky shores that were recently successfully invaded by the acorn barnacle Balanus glandula. We conducted a field experiment combining living Spartina transplants and artificial model plants in order to address the following questions: Does the native ecosystem engineer S. densiflora facilitate the invasion of rocky shores by B. glandula? If so, how much of this facilitation is caused by its physical structure alone? We found that S. densiflora had a positive effect on the invasive barnacle by trapping among its stems, the mussels, shells and gravels where B. glandula settles. Dislodged mussels, cobbles, and small shells covered and agglutinated by living barnacles were retained within the aboveground structures of S. densiflora while the control plots (without living or artificial plant structures) remained mostly bare throughout the experiment, showing how plant structures speed the colonization process. Moreover, transplanting living Spartina and artificial Spartina models led to a maximum increase in the area covered by barnacles of more than 1700% relative to the unvegetated control plots. Our study clearly shows how a native ecosystem engineers can enhance the success of invasive species and facilitate their local spread. [Copyright &y& Elsevier]

Barnacle feeding and respiration depend on the activity of feeding appendages known as cirri. We measured the oxygen consumption of individuals of the acorn barnacle Balanus glandula Darwin, 1854 to determine how changes in beating behavior, body size, and cirrus length affected energy demand. Respiration rates increased exponentially with body mass to the 0.66 power. Respiration rates did not differ significantly among pumping, normal, and fast beats, even though these beats involve different levels of cirral and opercular activity. Finally, barnacles from a location of high water motion exhibited significantly shorter cirri and lower oxygen consumption for a given body size than those from calmer waters. [ABSTRACT FROM AUTHOR]

Balanus glandula is a native barnacle of the rocky shores in the west coast of North America. Forty years after its introduction in Argentina, this species is the only barnacle dominating the high intertidal of local rocky shores and more interesting, it was also reported successfully colonizing soft-bottom salt marshes. In this study, we identified and characterized the substrata most successfully colonized by B. glandula in Patagonian salt marshes through descriptive and experimental means. We surveyed and compared two Patagonian salt marshes and the substrata colonized by B. glandula. Our results show that barnacles utilize more than 10 types of different substrata. Mussel valves were the most frequent type of substrata utilized in Riacho marsh, whereas the dominant halophyte Sarcocornia perennis was the substratum most utilized in Fracasso marsh where mussels were mostly absent. When the five most utilized substrata were experimentally offered, the halophyte shrub Limonium brasiliense was the most densely colonized of the experimental substrata, with the largest sizes and the lowest proportion of dead barnacles. Density and size of the barnacles recruited on plants were similar to that observed in nearby invaded rocky shores. Our study strongly suggests that soft-bottom environments, where hard substrata are available, have to be seriously considered when designing early detection plans targeting B. glandula and other similar rocky shore invasive species. [ABSTRACT FROM AUTHOR]

Abstract: Examples of morphological plasticity now exist across a wide range of taxa and experimental systems. Much of what we know about such plasticity comes from field and laboratory manipulations assessing the magnitude of plastic responses. However, we know much less about how – and how quickly – such changes occur, nor about how changes in form track natural environmental variation. Knowing more about plastic responses under natural conditions is important to help identify developmental costs and limits that may restrict the evolution of plasticity in variable environments. In this study, I measured leg and penis form plasticity in the common Pacific acorn barnacle Balanus glandula. A ten-week transplant experiment under natural conditions in the intertidal revealed: i) barnacles took longer to change leg form than previously thought, ii) response rates depended on transplant direction, and iii) barnacles changed leg length through a combined response of growing longer leg segments and adding more leg segments. Furthermore, a two-year survey of barnacle leg and penis form in natural populations revealed that barnacle leg and penis form varied in a manner consistent with adaptation to seasonal variation in wave height. Together, these results suggest that resource acquisition under natural conditions may be an important and underappreciated limit on morphological response times in natural systems, and shed light on how such changes occur during development. [Copyright &y& Elsevier]

Many aspects of barnacle body form are known to be developmentally plastic. Perhaps the most striking examples of such plasticity occur in their feeding legs and unusually long penises, the sizes and shapes of which can change dramatically and adaptively with changes in conspecific density and local water flow conditions. However, whether variation in overall appendage form is mirrored by structural responses in cuticle and muscle is not known. In order to determine how structural variation underlies phenotypic plasticity in barnacle appendages, we examined barnacles occurring at low and high population densities from one wave-protected and one wave-exposed site. We used histological sectioning and fluorescence microscopy of feeding legs and penises to compare cuticle thickness, muscle thickness, and muscle organization, and artificial penis inflation to compare penis extensibility. We observed striking differences in cuticle thickness, muscle thickness, and muscle organization between sites that differed in water velocity, but we found no clear differences associated with variation in conspecific density. Penis extensibility also did not differ consistently between sites. These results are consistent with an adaptive explanation for much of the remarkable and complex variation in barnacle feeding leg and penis morphology among sites that differ in water velocity. [ABSTRACT FROM AUTHOR]

Sex allocation theory for simultaneous hermaphrodites predicts increases in relative allocation to male-specific function as competition for fertilizations increases. Theoretical models developed specifically for competing acorn barnacles predict that the proportional allocation to male function increases toward an asymptote of 50% as the number of competitors for fertilizations increases. Experimental manipulations were used to investigate how mate competition affected both relative and absolute allocation to the sex functions for two species of acorn barnacle: Semibalanus balanoides and Balanus glandula. The ratio of male to female allocation did not increase with the number of competitors for either species. However, both species showed increased allocation to male function (estimated as total mass of sex-specific tissues) with increased crowding. Allocation to female function seemed to be limited by other factors and did not vary with mating group size as predicted. Allocation to male and female function were both positively related to body size, but a trade-off between male and female function, a key assumption of prior models, was not observed. [ABSTRACT FROM AUTHOR]

The article presents a study that deals with the role of low upwelling intensity in shaping the genetic structure and settlement rate of acorn barnacle Balanus glandula. It cites the influence of reproductive ouput, larval transport, survival, and settlement success on the generic identity of recruits from year to year. It uses a temporal and spatial sampling protocol to test for genetic heterogeneity among adults and recruits from multiple points along a 400 kilometer stretch of the Oregon coastline.

The goals of this study were to describe the diet and estimate the trophic level and food selection of Jenyns's sprat Ramnogaster arcuata, one of the common fishes in the Bahía Blanca estuary in Argentina. The copepods Acartia tonsa [53·7% index of relative importance ( I)] and Eurytemora americana (13·4% I), the mysid Arthromysis magellanica (13·9% I) and the small shrimp Peisos petrunkevitchi (8·2% I) were the most important food items for this species, and its diet exhibited monthly variability with respect to the principal prey categories. The zooplankton species in the study area consisted of 32 taxa. Acartia tonsa was the most abundant species [54% individuals ( N) m], followed by Balanus glandula (13·8% N m) and E. americana (10·1% N m). The rest of the zooplankton groups represented <3% N m. The most preferred items throughout the year were A. magellanica and Idotea sp. The trophic level value estimated was 3·1. [ABSTRACT FROM AUTHOR]

The article presents a study on the developmental coupling between multiple plastic traits of Balanus glandula that showed that barnacle legs and penises possess the capacity for independent and modular adaptive plasticity. The penis form and leg form of barnacles are both highly plastic traits that varied in response to difference in conspecific density and water velocity. Both penis length and leg length in the barnacles varied in parallel with variation in wave-exposure but varied in opposite directions with variation in conspecific density.

Abstract: 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. [Copyright &y& Elsevier]