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Metacestode infestation of Semibalanus balanoides (L., 1767) and Balanus crenatus Bruguiеre, 1789, collected in the Barents and White Seas and in the northern part of the Sea of Okhotsk in 2020 and 2021, respectively, was studied. A total of 313 S. balanoides from Mogilnaya Bay of Kildin Island (Barents Sea) and isolated mature wrinkled barnacles B. crenatus, two and four specimens from the Pechora Sea and Kandalaksha Bay of the White Sea, respectively, were examined in 2020. Metacestodes Fimbriarioides intermedia (Fuhrmann, 1913) (Cyclophyllidea, Hymenolepididae) were found in 1.0 ± 0.6% of S. balanoides in the Barents Sea with an invasion intensity (I. I.) of 2–5 specimens, and in one of two B. crenatus from the Pechora Sea (I. I. 15 specimens). For the first time, in both B. crenatus from the Pechora Sea, taken from the valves of the mussel Mytilus edulis, metacestodes Microsomacanthus sp. I (I. I. 13 and 20 specimens) with proboscis hooks 38–41 (39.4 ± 0.1) µm long and blades of 9.5–11 (10.7 ± 0.1) µm were obtained. One of four B. crenatus from the Kandalaksha Bay was infected with another Microsomacanthus sp. II (I. I. 19 specimens) with proboscis hooks 44.0–49.5 (45.7 ± 0.5) µm long and blades 14.0–16.0 (14.8 ± 0.07) µm long. A total of 362 S. balanoides were collected and dissected in Gizhiginskaya Bay of the northern part of the Sea of Okhotsk in 2021, of which 8.0 ± 1.4% were infected with F. intermedia metacestodes (I. I. 1–19 specimens). Study results of the infestation of S. balanoides on the Koni-Pyagin coast of the Sea of Okhotsk (according to the collections of 2006–2007) were supplemented and clarified. Description of metacestodes and the taxonomic affiliation of cysticercoids Microsomacanthus spp. are given. [ABSTRACT FROM AUTHOR]

Abstract Background Natural populations inhabiting the rocky intertidal experience multiple ecological stressors and provide an opportunity to investigate how environmental differences influence microbiomes over small geographical scales. However, very few microbiome studies focus on animals that inhabit the intertidal. In this study, we investigate the microbiome of the intertidal barnacle Semibalanus balanoides. We first describe the microbiome of two body tissues: the feeding appendages, or cirri, and the gut. Next, we examine whether there are differences between the microbiome of each body tissue of barnacles collected from the thermally extreme microhabitats of the rocky shores’ upper and lower tidal zones. Results Overall, the microbiome of S. balanoides consisted of 18 phyla from 408 genera. Our results showed that although cirri and gut microbiomes shared a portion of their amplicon sequence variants (ASVs), the microbiome of each body tissue was distinct. Over 80% of the ASVs found in the cirri were also found in the gut, and 44% of the ASVs found in the gut were also found in the cirri. Notably, the gut microbiome was not a subset of the cirri microbiome. Additionally, we identified that the cirri microbiome was responsive to microhabitat differences. Conclusion Results from this study indicate that S. balanoides maintains distinct microbiomes in its cirri and gut tissues, and that the gut microbiome is more stable than the cirri microbiome between the extremes of the intertidal.

The northern acorn barnacle (Semibalanus balanoides) is a robust system to study the genetic basis of adaptations to highly heterogeneous environments. Adult barnacles may be exposed to highly dissimilar levels of thermal stress depending on where they settle in the intertidal (i.e., closer to the upper or lower tidal boundary). For instance, barnacles near the upper tidal limit experience episodic summer temperatures above recorded heat coma levels. This differential stress at the microhabitat level is also dependent on the aspect of sun exposure. In the present study, we used pool‐seq approaches to conduct a genome wide screen for loci responding to intertidal zonation across the North Atlantic basin (Maine, Rhode Island, and Norway). Our analysis discovered 382 genomic regions containing SNPs which are consistently zonated (i.e., SNPs whose frequencies vary depending on their position in the rocky intertidal) across all surveyed habitats. Notably, most zonated SNPs are young and private to the North Atlantic. These regions show high levels of genetic differentiation across ecologically extreme microhabitats concomitant with elevated levels of genetic variation and Tajima's D, suggesting the action of non‐neutral processes. Overall, these findings support the hypothesis that spatially heterogeneous selection is a general and repeatable feature for this species, and that natural selection can maintain functional genetic variation in heterogeneous environments. [ABSTRACT FROM AUTHOR]

Acorn barnacle adults experience environmental heterogeneity at various spatial scales of their circumboreal habitat, raising the question of how adaptation to high environmental variability is maintained in the face of strong juvenile dispersal and mortality. Here, we show that 4% of genes in the barnacle genome experience balancing selection across the entire range of the species. Many of these genes harbor mutations maintained across 2 My of evolution between the Pacific and Atlantic oceans. These genes are involved in ion regulation, pain reception, and heat tolerance, functions which are essential in highly variable ecosystems. The data also reveal complex population structure within and between basins, driven by the trans-Arctic interchange and the last glaciation. Divergence between Atlantic and Pacific populations is high, foreshadowing the onset of allopatric speciation, and suggesting that balancing selection is strong enough to maintain functional variation for millions of years in the face of complex demography. [ABSTRACT FROM AUTHOR]

The mannose-6-phosphate isomerase (Mpi) locus in Semibalanus balanoides has been studied as a candidate gene for balancing selection for more than two decades. Previous work has shown that Mpi allozyme genotypes (fast and slow) have different frequencies across Atlantic intertidal zones due to selection on postsettlement survival (i.e., allele zonation). We present the complete gene sequence of the Mpi locus and quantify nucleotide polymorphism in S. balanoides, as well as divergence to its sister taxon Semibalanus cariosus. We show that the slow allozyme contains a derived charge-altering amino acid polymorphism, and both allozyme classes correspond to two haplogroups with multiple internal haplotypes. The locus shows several footprints of balancing selection around the fast/slow site: an enrichment of positive Tajima's D for nonsynonymous mutations, an excess of polymorphism, and a spike in the levels of silent polymorphism relative to silent divergence, as well as a site frequency spectrum enriched for midfrequency mutations. We observe other departures from neutrality across the locus in both coding and noncoding regions. These include a nonsynonymous trans-species polymorphism and a recent mutation under selection within the fast haplogroup. The latter suggests ongoing allelic replacement of functionally relevant amino acid variants. Moreover, predicted models of Mpi protein structure provide insight into the functional significance of the putatively selected amino acid polymorphisms. While footprints of selection are widespread across the range of S. balanoides, our data show that intertidal zonation patterns are variable across both spatial and temporal scales. These data provide further evidence for heterogeneous selection on Mpi. [ABSTRACT FROM AUTHOR]

The intertidal population of the barnacles Semibalanus balanoides has been explored in the estuarine zone of the Tuloma River at the end of the Kola Bay for the first time. Barnacles S. balanoides are typical species for the littoral zone of the northern seas, they populate both the high and low salinity areas along the coast of the Barents Sea. The ecology and distribution of barnacle population in estuarine intertidal zones of the Barents Sea are not studied previously, and under the critical salinity conditions of any estuary, in particular. The investigation have been carried out on the littoral of the western (left) shore of the southern tribe of the Kola Bay – the estuary section from the Tuloma bridge to the Cape Elovy. The studied site is a sandy-boulder beach with stony bars, its length is about 1 150 m, the area is about 126 500 m2. Counting the number of S. balanoides in clusters has been performed on site (without removal of the copepods from the population) by the standard method for intertidal sampling. Simultaneously with the defining the number of barnacles for the period 2003–2014, the measurements of salinity and temperature of water and air have been made. The peculiarity of the estuarine barnacle population is their complete absence in the upper horizon of the littoral, and in the middle and the lower horizons they are found only within the channels of the littoral streams (3–20 specimens in the sample). For the first time the abundance and biomass of barnacles S. balanoides in this estuarine population has been determined, and the causes of their narrow-local distribution on the estuary littoral of the Tuloma River have been revealed. The main ecological factors determining the abundance and specific distribution of barnacles under the conditions of estuarine littoral have been established. The regular increase in the density of adult S. balanoides settlements along the gradient of water salinity from the Tuloma River to the sea has been shown. The long-term fluctuations in the abundance of barnacle S. balanoides have been found, associated, obviously, with climate changes.

Abstract: Predators can impact competition among prey by altering prey density via consumption or by causing prey to modify their traits or foraging behavior. Yet, differences between these two mechanisms may lead to different cascading impacts on lower trophic levels. Using a crab‐snail‐barnacle rocky intertidal food chain, we tested the effects of predation risk from crabs (top predators) on intraspecific competition among snails (intermediate consumers) and emergent indirect effects on the density of and competition among barnacles (basal resources). The per capita foraging and growth rates of snails declined with high conspecific density. Predation risk from crabs, which caused even larger reductions in snail foraging and growth, weakened competition among snails, whereas a 45% increase in barnacle density had no detectable effect on snail competition. Intraspecific competition between barnacles, however, depended on the interactive effects of barnacle density, snail density, and crab predation risk. Barnacles developed hummocking morphologies as they grew and competed for space. Hummock formation (a proxy for competition) increased as a result of either greater initial barnacle density or reduced snail foraging pressure, but these effects depended on predation risk. The effects of crab predation risk on snail foraging behavior weakened an otherwise strong relationship between barnacle density and hummock development: hummocking increased with barnacle density in the absence of crabs but remained relatively high when crabs were present. In communities with similar final barnacle densities, hummocking was more common in those with crabs than those without crabs. The extent to which predators can drive trophic cascades by suppressing the foraging rates of their prey is highly context‐dependent: the positive trait‐mediated indirect effect of predators on basal resource abundance is stronger when many prey respond simultaneously to the threat of predation. However, our results demonstrate that top predators can also enhance competition among basal resources even when their indirect effect on resource abundance is relatively weak. Hence, the cascading effects of predators on competition within lower trophic levels may play an important but under‐appreciated role in the dynamics of basal resource populations and the communities they support. A plain language summary is available for this article. [ABSTRACT FROM AUTHOR]

Marine benthic populations are dependent on early life-history stages surviving multiple population bottlenecks. Failure at one or several of these bottlenecks can alter species’ patterns of distribution and abundance. The barnacle Semibalanus balanoides is found along temperate and sub-arctic shorelines of the Atlantic and Pacific Oceans. Over the past century the southern range limits of S. balanoides have shifted hundreds of kilometres poleward on both coasts of the Atlantic. Here we tested if temperature limits fertilization and used these data, along with those from previous studies, to create mechanistic biogeographic models to understand which potential population bottlenecks in the early life-history of S. balanoides influence its distribution and abundance. In the western Atlantic survival of new recruits is probably more important in setting the southern range limit than the effects of temperature on early life-history stages because fertilization, brooding and the probability of larval release matching phytoplankton availability were all predicted to be high near the historical range edge. Phytoplankton mismatch may partially explain the ephemeral nature of S. balanoides in some parts of the English Channel. Further south along the coast of France predicted brooding success was reduced in a pattern consistent with historical range shifts in this region. Within Galicia, Spain fertilization was predicted to be low near the southern limit, and likely plays an important role in setting this range edge. Mismatches between phytoplankton abundance and larval release in Galicia may further limit reproductive success within this region. [ABSTRACT FROM AUTHOR]

Abstract: Range shifts due to annual variation in temperature are more tractable than range shifts linked to decadal to century long temperature changes due to climate change, providing natural experiments to determine the mechanisms responsible for driving long‐term distributional shifts. In this study we couple physiologically grounded mechanistic models with biogeographic surveys in 2 years with high levels of annual temperature variation to disentangle the drivers of a historical range shift driven by climate change. The distribution of the barnacle Semibalanus balanoides has shifted 350 km poleward in the past half century along the east coast of the United States. Recruits were present throughout the historical range following the 2015 reproductive season, when temperatures were similar to those in the past century, and absent following the 2016 reproductive season when temperatures were warmer than they have been since 1870, the earliest date for temperature records. Our dispersal dependent mechanistic models of reproductive success were highly accurate and predicted patterns of reproduction success documented in field surveys throughout the historical range in 2015 and 2016. Our mechanistic models of reproductive success not only predicted recruitment dynamics near the range edge but also predicted interior range fragmentation in a number of years between 1870 and 2016. All recruits monitored within the historical range following the 2015 colonization died before 2016 suggesting juvenile survival was likely the primary driver of the historical range retraction. However, if 2016 is indicative of future temperatures mechanisms of range limitation will shift and reproductive failure will lead to further range retraction in the future. Mechanistic models are necessary for accurately predicting the effects of climate change on ranges of species. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the role of larger‐scale processes in modulating the assembly, structure, and dynamics of communities is critical for forecasting the effects of climate‐change and managing ecosystems. Developing this comprehensive perspective is difficult though, because species interactions are complex, interdependent, and dynamic through space and time. Typically, experiments focus on tractable subsets of interactions that will be most critical to investigate and explain shifts in communities, but qualitatively base these choices on experience, natural history, and theory. One quantitative approach to identify the putative forces regulating communities, without reducing system complexity, is estimating transition probabilities among species occupying space (i.e., multispecies Markov chain models). Although not mechanistic, these models estimate the relative frequency and importance of ecological pathways in community assembly and dynamics, and can serve as a framework to identify how pathways change across large scales and which are most important to investigate further. Here, we demonstrate this method in the Gulf of Maine (GOM) intertidal zone, where research has largely focused on the local‐scale processes that influence communities, while the mechanisms responsible for more regional shifts in communities are less clear. Transition probabilities of faunal elements were quantified bimonthly for ~2.5 yr in local intertidal communities at three replicate sites in the southern, mid‐coast, and northern GOM. Transitions related to mortality, colonization, and replacement by mussels, barnacles, red algae, and encrusting corallines differed regionally, suggesting specific pathways related to consumer pressure and recruitment vary across the GOM with shifting intertidal community structure. Combined with species abundance data and insights from previous research, we develop and evaluate the pathways by which communities likely change in the GOM. Species interactions in local communities can be complex, and this complexity should be incorporated into hypothesis building, experiments, theory, interpretations, and forecasts in ecology. Such a comprehensive approach will be critical to understand how regional shifts in local interactions can drive large‐scale community change. [ABSTRACT FROM AUTHOR]

In intertidal communities, consumers (especially carnivorous gastropods) have historically been thought to exert strong top-down control on community composition by regulating competitively dominant mussels and barnacles. This paradigm was formulated based on wire mesh cage exclusion experiments, which have well-known artifacts such as altering hydrodynamics and excluding non-target, but potentially important, consumer species. Recent research highlights the potential importance of multiple consumers that are often subtle and transient, as well as the modifications of consumer pressure by spatial and temporal environmental variability and bottom-up processes. Manipulative experiments that target individual taxa will be essential to more clearly identify their roles in complex ecological communities. The predatory gastropod Nucella lapillus has long been considered an important consumer controlling the structure and dynamics of intertidal communities in the Gulf of Maine. To test the role of N. lapillus in shaping community structure, we manually reduced its densities for 2.33 years. Species composition, stable stage community composition (based on a Markov model), and transition probabilities (as measures of ecological pathway strength) were compared between treatments (control vs. density reductions), and among seasons (spring, summer, fall, winter). In contrast to previous studies, exclusions had no effect on community composition or long-term Markov model predictions of stable stage community structure. Reducing N. lapillus abundance increased the persistence and reduced the mortality of the barnacle Semibalanus balanoides in the model, but did not affect blue mussels, Mytilus edulis , in a similar way. Reducing N. lapillus abundance had additional indirect effects of increasing Ralfsia spp. mortality and increasing hydroid persistence. Despite differences in transition probabilities among treatments, compensatory changes in direct and indirect pathways led to communities that converged over the long-term. Our results contrast previous estimates of the role of N. lapillus in intertidal communities and might reflect low mussel recruitment, predation by alternate consumers (e.g., C. maenas , C. borealis , Tautogolabrus adspersus , birds), or spatial and/or temporal environmental variation that influenced the role of N. lapillus in structuring these communities. The role of N. lapillus may be more limited, or variable, than often assumed in the Gulf of Maine, and the methods manipulating broad functional groups such as “consumers”, though useful in developing basic conceptual models, blur the effects of individual species in community assembly and dynamics. [ABSTRACT FROM AUTHOR]

Studies identifying interactions between biological invasions and other stressors have generally focussed on quantifying their cumulative effects on mature species assemblages. In benthic systems, however, early life history processes are key determinants of assemblage structure and functioning. This study tested whether the presence of an invasive species affected early life history processes of two common barnacle species and whether this was affected by a second common stressor, nutrient enrichment. The results of a field experiment identified and characterised the effects of an invasive oyster, Crassostrea gigas , on the early life history processes of the two barnacle species under ambient and enriched nutrient conditions. In the presence C. gigas , the invasive barnacle Austrominius modestus , had a lower recruitment rate, however, there was no effect of the presence of C. gigas on native barnacle, Semibalanus balanoides , recruitment. Nutrient enrichment also reduced the recruitment rate of A. modestus , however, there was no evidence of synergistic or antagonistic interactions between these stressors, indicating their cumulative effects were additive. There was no effect of nutrient enrichment on native barnacle recruitment. Our results show that the presence of an invasive oyster and nutrient enrichment altered the recruitment of another non-native benthic species. These findings emphasise the importance of considering early life history processes when assessing effects of multiple stressors on communities. [ABSTRACT FROM AUTHOR]

Spatial patterns in aggregations form as a result of the interplay between costs and benefits experienced by individuals. Such self-organisation of aggregations can be explained using a zonal model in which a short-range zone of repulsion and longer-range zone of attraction surrounding individuals leads to emergent pattern properties. The signal of these processes can be detected using spatial pattern analyses. Furthermore, in sessile organisms, post-settlement mortality reveals the relative costs and benefits of positions within the aggregation. Acorn barnacles are known to require contact with conspecifics for reproduction and are therefore believed to aggregate for this purpose; isolated individuals may also be more susceptible to abiotic stress and predation. At short distances, however, competition for space and resources is likely to occur. In this study spatial patterns of barnacles ( Semibalanus balanoides L.) were analysed using pair-correlation functions. Individuals were dispersed at distances below 0.30 cm, but peak relative density occurred at a distance of 0.36 cm from conspecifics. This is much closer than required for reproductive access, implying a strong aggregative drive, up to the point of physical contact with neighbours. Nevertheless, analysis of dead barnacles illustrated that such proximity carries a cost as barnacles with many neighbours were more likely to have died. The inferences obtained from these patterns are that barnacles aggregate as closely as they can, and that local neighbourhood competition is a powerful determinant of mortality. These processes give rise to the observed pattern properties. [ABSTRACT FROM AUTHOR]

We investigated the nonconsumptive effects (NCEs) of predatory dogwhelks (Nucella lapillus) on intertidal barnacle (Semibalanus balanoides) recruitment through field experiments on the Gulf of St. Lawrence coast and the Atlantic coast of Nova Scotia, Canada. We studied the recruitment seasons (May-June) of 2011 and 2013. In 2011, the Gulf coast had five times more nearshore phytoplankton (food for barnacle larvae and recruits) during the recruitment season and yielded a 58% higher barnacle recruit density than the Atlantic coast at the end of the recruitment season. In 2013, phytoplankton levels and barnacle recruit density were similar on both coasts and also lower than for the Gulf coast in 2011. Using the comparative-experimental method, the manipulation of dogwhelk presence (without allowing physical contact with prey) revealed that dogwhelk cues limited barnacle recruitment under moderate recruit densities (Atlantic 2011/2013 and Gulf 2013) but had no effect under a high recruit density (Gulf 2011). Barnacle recruits attract settling larvae through chemical cues. Thus, the highest recruit density appears to have neutralized dogwhelk effects. This study suggests that the predation risk perceived by settling larvae may decrease with increasing recruit density and that prey food supply may indirectly influence predator NCEs on prey recruitment. [ABSTRACT FROM AUTHOR]

The invasive barnacle Austrominius (= Elminius) modestus has been present in Europe since the 1940s, and has recently been recorded to outnumber native barnacle species at some locations, including an Irish marine nature reserve. It has been suggested that these increases in abundance following a lag phase since establishment, represent the awakening of an ‘ecological sleeper’, due to changes in environmental conditions. Austrominius modestus was first recorded on the Isle of Cumbrae, Scotland in 1955, and was reported to be well established on the island by 2007. Since this location is close to the northern limit of the invaded range of A. modestus , it has been chosen as a site for the long term monitoring of this species. Quantitative and semi-quantitative surveys of the abundance of A. modestus , together with the native barnacle species Chthamalus montagui and Semibalanus balanoides , have been made on the island on a biannual basis since 2009. This study examined changes in the abundances of these three species from 2009 to 2013, and reports on the present status of this invasive species on the island. Austrominius modestus was found at all sites surveyed, but did not outnumber native barnacle species at any site. Semibalanus balanoides , a cold water boreal species, was the most abundant barnacle species at most sites from 2009 to 2013. All three barnacle species underwent a decline in 2011, but had increased in abundance by 2013. Despite undergoing the smallest increase in abundance between 2011 and 2013, S. balanoides remains the dominant barnacle species on the Isle of Cumbrae. Nearly sixty years after its initial discovery on the island, A. modestus is widespread, however it has not outnumbered native species, which continue to recruit at high densities. This competitive pressure makes it unlikely that A. modestus will outnumber native barnacle species at this location, close to its northern limit, in the near future. [ABSTRACT FROM AUTHOR]

Geographic distributions of species are frequently influenced by temperature and as a result, there is considerable interest in predicting the effect of climate change on biogeography. Previous studies have found strong correlations between sea surface temperature and recruitment in the acorn barnacle Semibalanus balanoides , an important member of temperate intertidal communities in the Northern Hemisphere. The underlying mechanism that drives this relationship is, however, unknown. The hypothesis tested here is that variation in recruitment is determined by temperature-induced variation in survival of brooded embryos. Brooding adults were held under several environmentally-relevant temperature conditions from 7 °C to 13 °C until eggs were ready to hatch. There was no significant effect of temperature on embryonic development rate. Brooding individuals held at colder temperatures had more than twice the reproductive mass of those held at warmer temperatures. This mass difference is caused by an over three-fold larger number of embryos surviving in the coldest treatment (7 °C) compared to the warmest treatment (13 °C). Temperature-induced variation in number of surviving embryos likely contributes to differences in recruitment following cold winters vs. warm winters. Such temperature-dependent variation in recruitment has been shown to cause year to year fluctuations in the positions of the geographic limits of the species in Southwest England, France, and Spain. This study illustrates the key role of adult input into the larval pool in generating variation in recruitment and its influence on biogeography. [ABSTRACT FROM AUTHOR]

We tested whether the patchiness of barnacle settlement was determined by spatial (local) differences in settling and mortality rates. During the period of 2004-2011, annual photo-registration of a barnacles Semibalanus balanoides population was conducted on six flat rocks in the White Sea intertidal zone (Arctic). The average adult population density was 48 ind dm, and the average barnacle age was 3-4 years. According to age structure, during the first year, the number of recruits dropped by three to fourfold; while in the following 2 years, the population density remained nearly the same. The effect of ice friction influence was not recorded, although the rocks were covered with ice in winter. Settling peaks were recorded in 2005, 2007, and 2009. No correlation was observed between the recruit and adult distribution during 2 years of intense settlement. The death rate was uneven on different quadrates along the transects but did not correlate with population density. Because high settling rates and mortality are not linked to specific sites, this suggests that population patchiness is not spatially stable. [ABSTRACT FROM AUTHOR]

We propose an integrative approach that explains patterns of recruitment to adult populations in sessile organisms by considering the numbers of individuals and their body size. A recruitment model, based on a small number of parameters, was developed for sessile organisms and tested using the barnacle Semibalanus balanoides, a marine invertebrate inhabiting North Atlantic intertidal shores. Incorporating barnacle body size improved model fit beyond that based on density alone, showing that growth played an important role in how resource limitation affected survival. Our approach uncovered the following: First, changes in the shape of the recruitment curve resulted from the balance between individual growth and mortality. Second, recruitment was limited by the least plastic trait used to characterise body size, operculum area. Basal area, a trait that responded to increases in barnacle density, did not contribute significantly to explain patterns of recruitment. Third, some temporal variation is explained by changes in the amount of space occupied by shells of dead barnacles: at high cover barnacles are densely packed and these shells remain long after death. Fourth, seasonal variation and spatial variation in survival can be separated from that resulting from resource limitation; survival was predicted for two different shores and four sampling times using a single recruitment model. We conclude that applying this integrative approach to recruitment will lead to a considerable advance in understanding patterns of mortality of early stages of sessile organisms. [ABSTRACT FROM AUTHOR]

Several previous studies have reported high levels of genetic differentiation between populations inside European Marine Reserves and their adjacent coastlines for a direct-developing species. These studies suggest that sea loughs may not represent the most suitable sites for inclusion into Marine Protected Area (MPA) or Marine Reserve networks as they are not well connected to other populations. However, many marine species have pelagic larvae, and the connectivity of populations of such species inside sea loughs with non-lough populations remains unknown. Here, I investigated the levels of gene flow between populations of the acorn barnacle Semibalanas balanoides inside and outside Strangford Lough, Northern Ireland; this species has a long-lived pelagic larvae (4-6 weeks). There were no significant differences in the levels of genetic diversity between sea lough and non-lough populations and no evidence for genetic differentiation between any of the populations examined; the populations appear well mixed and well connected, in contrast to what has been reported for a previous direct-developing species. [ABSTRACT FROM AUTHOR]

Understanding the patterns of genetic variation within and among populations is a central problem in population and evolutionary genetics. We examine this question in the acorn barnacle, Semibalanus balanoides, in which the allozyme loci Mpi and Gpi have been implicated in balancing selection due to varying selective pressures at different spatial scales. We review the patterns of genetic variation at the Mpi locus, compare this to levels of population differentiation at mtDNA and microsatellites, and place these data in the context of genome-wide variation from high-throughput sequencing of population samples spanning the North Atlantic. Despite considerable geographic variation in the patterns of selection at the Mpi allozyme, this locus shows rather low levels of population differentiation at ecological and trans-oceanic scales (FST ∼ 5%). Pooled population sequencing was performed on samples from Rhode Island (RI), Maine (ME), and Southwold, England (UK). Analysis of more than 650 million reads identified approximately 335,000 high-quality SNPs in 19 million base pairs of the S. balanoides genome. Much variation is shared across the Atlantic, but there are significant examples of strong population differentiation among samples from RI, ME, and UK. An FST outlier screen of more than 22,000 contigs provided a genome-wide context for interpretation of earlier studies on allozymes, mtDNA, and microsatellites. FST values for allozymes, mtDNA and microsatellites are close to the genome-wide average for random SNPs, with the exception of the trans-Atlantic FST for mtDNA. The majority of FST outliers were unique between individual pairs of populations, but some genes show shared patterns of excess differentiation. These data indicate that gene flow is high, that selection is strong on a subset of genes, and that a variety of genes are experiencing diversifying selection at large spatial scales. This survey of polymorphism in S. balanoides provides a number of genomic tools that promise to make this a powerful model for ecological genomics of the rocky intertidal. [ABSTRACT FROM AUTHOR]

Abstract: Amphibalanus (=Balanus) amphitrite is a tropical/sub-tropical barnacle species which is naturally exposed to sea temperatures of 16–27 °C throughout its larval development. An established technique widely employed by investigators of A. amphitrite settlement involves the storage of cyprids at 4–6 °C prior to their use in bioassays. Our study focuses on the effects on ageing temperature on settlement and discrimination of A. amphitrite larvae. Using cyprids aged at 2 temperatures, 6° and 23 °C, we confirmed the general trend in the literature that young d0 cyprids of this species do not appear competent to settle. Performing cyprid settlement assays at 20, 25 or 28 °C, we observed that the proportion of settled cyprids when incubated at 28 °C was greater than that of cyprid incubated at 25 °C and 20 °C. Settlement rates of cyprids aged at 6 °C and 23 °C increased relative to age from d1 to d10 irrespective of temperature. Cyprids lost the ability to undergo attachment and metamorphosis at d14 or d15 when aged at 6 °C or 23 °C respectively. In the choice assays executed in this study, cyprids generally chose to settle on adult extract-treated areas. But localised settlement on adult extract-treated areas decreased with time. Choice settlement assays at set age intervals during the cypris larval stage showed that cyprids were able to discriminate between con- and allospecific adult extracts. The duration and the temperature of cyprids storage influenced selectivity. [Copyright &y& Elsevier]

ABSTRACT Aim Marine sessile inter-tidal invertebrates are expected to undergo shifts in distribution due to climate change. Using a combination of survey and transplant data with thermal modelling, we investigated the role of climate on the poleward contraction of the southern range edge of the north temperate barnacle Semibalanus balanoides. Location Western Atlantic of the United States. Methods Barnacle surveys were conducted along the east coast of the United States in 1963 and 2007. Presence, absence and abundance data were collected and the time periods were compared. Transplant experiments monitoring survival with relation to temperature were conducted upon S. balanoides along the more southerly portion of their range, and modelling predicting barnacle survival with relation to biogeography was completed. Results The southern limit of S. balanoides has contracted approximately 350 km to the north. Main conclusions The changes thus far observed in climate along the east coast of the United States have contributed to the southern limit range contraction of S. balanoides. Further changes in the biogeography of S. balanoides are expected with continued climate warming. [ABSTRACT FROM AUTHOR]

The reproductive phenology and size of populations of Semibalanus balanoides were studied at four sites along a latitudinal gradient in the Bay of Fundy. Animals were collected from May 2006 through January 2007, their basal widths measured and the first appearance of immature oocytes, mature oocytes, brooded embryos, and sperm scored. Proceeding from south to north, there was a significant decline in the size of the barnacles and a delay in appearance of all stages. The possible effects of temperature and turbidity are discussed. [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]

Population genetic characteristics are shaped by the life-history traits of organisms and the geologic history of their habitat. This study provides a neutral framework for understanding the population dynamics and opportunities for selection in Semibalanus balanoides, a species that figures prominently in ecological and evolutionary studies in the Atlantic intertidal. We used mitochondrial DNA (mtDNA) control region (N = 131) and microsatellite markers (∼40 individuals/site/locus) to survey populations of the broadly dispersing acorn barnacle from 8 sites spanning 800 km of North American coast and 1 site in Europe. Patterns of mtDNA sequence evolution were consistent with larger population sizes in Europe and population expansion at the conclusion of the last ice age, approximately 20 000 years ago, in North America. A significant portion of mitochondrial diversity was partitioned between the continents (ϕST = 0.281), but there was only weak structure observed from mtDNA within North America. Microsatellites showed significant structuring between the continents (FST = 0.021) as well as within North America (FST = 0.013). Isolation by distance in North America was largely driven by a split between populations south of Cape Cod and all others (P < 10−4). The glacial events responsible for generating allelic diversity at mtDNA and microsatellites may also be responsible for generating selectable variation at metabolic enzymes in S. balanoides. [ABSTRACT FROM PUBLISHER]

Predators can initiate trophic cascades by consuming and/or scaring their prey. Although both forms of predator effect can increase the overall abundance of prey's resources, nonconsumptive effects may be more important to the spatial and temporal distribution of resources because predation risk often determines where and when prey choose to forage. Our experiment characterized temporal and spatial variation in the strength of consumptive and nonconsumptive predator effects in a rocky intertidal food chain consisting of the predatory green crab (Carcinus niaenas), an intermediate consumer (the dogwhelk, Nucella lapillus), and barnacles (Sernihalanus halanoides) as a resource. We tracked the survival of individual barnacles through time to map the strength of predator effects in experimental communities. These maps revealed striking spatiotemporal patterns in Nucella foraging behavior in response to each predator effect. However, only the nonconsumptive effect of green crabs produced strong spatial patterns in barnacle survivorship. Predation risk may play a pivotal role in determining the small-scale distribution patterns of this important rocky intertidal foundation species. We suggest that the effects of predation risk on individual foraging behavior may scale up to shape community structure and dynamics at a landscape level. [ABSTRACT FROM AUTHOR]