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Anelasma squalicola is a parasitic barnacle of members of the deep-water shark families Etmopteridae, Pentanchidae and Scyliorhinidae. We report the first published confirmation of this species in the Eastern Pacific Ocean, based on material collected off Costa Rica, its first record as a parasite of the Ninja lantern shark, Etmopterus benchley (Etmopteridae), and a new size record for the host. The information presented herein expands the knowledge (distribution and host usage) of this enigmatic species.

The settlement of intertidal barnacles Chthamalus spp. was measured for an entire recruitment season at 3 sites separated by 100 m in Baja California, Mexico. During a 10 d pulse that accounted for nearly 30% of yearly settlement, coastal wind speed and direction, nearshore water column temperature, and current velocities were also measured. During this period, strong internal tidal forcing was observed, with short episodes (1-1.5 h) of rapid fluctuations in water column temperature, stratification, and currents. Chthamalus spp. settlement was significantly and positively correlated with cumulative high-frequency fluctuations in temperature, thermal stratification, and surface current flows, but not with onshore winds. Furthermore, the spatial pattern in the number of settlers was correlated with the angle of propagation estimated for onshore-moving internal waves, potentially modulated by nearshore bathymetry. This relationship between Chthamalus spp. settlement and high-frequency changes in water column temperature was also shown for a site in La Jolla, California, USA, but not for a similar barnacle, Balanus glandula, suggesting that interspecific differences in larval behavior and nearshore depth distribution may translate into differences in transport. Our results suggest that both the number of settlers at shore and their spatial pattern can be modulated by the intensity and direction of internal wave events, at least during peak settlement periods. Future research should consider both the intensity and geometry of internal-wave-induced variability in the nearshore, as well the small-scale features of coastal geomorphology and bathymetry.

The role of cascades in natural communities has been extensively studied, but interactions between trophic and facilitation cascades are unexplored. In the White Sea (65°N) shallow subtidal, bivalve primary facilitators provide hard substrate for secondary facilitator barnacles, that, in turn, provide substrate for conspecifics, ascidians, red algae and multiple associated organisms, composing a multi-level facilitation cascade. Previous research revealed that predation by the whelk Boreotrophon clathratus accounts for ~7% of adult barnacle mortality. Low whelk abundance limits their effect, with barnacles living on conspecifics several times more vulnerable to predation than those living on primary substrate. Trophic cascades can selectively shield foundation species from consumers, and hence may affect the structure and length of facilitation cascades. We tested the hypothesis that low abundance of the whelks results from mesopredator predation on their juveniles. Depending on the magnitude of the effect, this would mean that a trophic cascade controls the abundance of barnacles on all substrates or only barnacles living on conspecifics. We also suggested that barnacles on primary substrates and conspecifics facilitate different dependent assemblages. We manipulated the presence of crab and shrimp mesopredators in field caging experiments to assess their effect on whelk recruitment. In a field survey, we compared the assemblages of sessile macrobenthic organisms associated with barnacles living on different substrates. Caging experiments evidenced that crab and shrimp mesopredators reduce whelk recruitment by 4.6 times. Field data showed that barnacles on primary substrate and on conspecifics promote different dependent assemblages including secondary facilitator ascidians. Although mesopredators do not shield barnacles from elimination, their absence would restrict them from living on conspecifics. Barnacles on conspecifics are functionally different from barnacles on primary substrate, and can be considered a separate level of the facilitation cascade. Trophic cascades thus can generate community-wide effects on facilitation cascades by affecting their structure and possibly length.

Barnacles are common epibionts on a wide range of marine organisms, including turtles. Chelonibia testudinaria is a successful epibiotic barnacle species, and mainly turtles are responsible for their wide range dispersal. In the present study, the mitochondrial Cytochrome Oxidase I (COI) gene haplotypes of C. testudinaria from Caretta caretta hosts were evaluated. The samples were collected from three dead C. caretta turtle carapaces in 2014 from the Middle East Technical University, Institute of Marine Sciences coastline. Results were also compared with those samples submitted to databases (NCBI and BOLD-system, 139 in total). By comparison, three clades were recorded like previous studies: the Atlantic-Mediterranean clade (Clade-α), the IndianPacific Ocean clade (Clade-β), and Magdalena Bay (Eastern Pacific- Clade-) clade; all samples collected from Turkish shores clustered in the Atlantic-Mediterranean group (Clade-α). The gene flow between the three clades was deficient and highly significant (0.02, 0.03, and 0.03, respectively). According to network age estimation, present study samples’ clade (Clade-α) diverged from the Clade-β approximately 200 kya (SDs=0.22, SDy=4402.90) and Clade- 130 kya (SDs=0.17, SDy=3494.55). In the present study, eight haplotypes were observed in total, two of which were specific to the region.

Spatiotemporal relationships between developmental stages (cydippid, transition and adult) of the comb jelly Mnemiopsis leidyi and environmental parameters were seasonally evaluated using the random forest (RF) model along the Iranian coasts of the Caspian Sea. The mean density of M. leidyi in spring, summer, autumn and winter were 8, 54, 130, and 15 ind m−3, respectively. The density of various stages, particularly cydippid, showed a decreasing trend with increase in depth. Cydippids had the highest abundance with a lower percentage in the deeper layers and colder seasons. Temperature was found to be the most influential parameter on the distribution of M. leidyi’s life stages, particularly cydippids, with a stronger effect in spring and summer. The highest densities for all life stages were observed above 20 °C with an explosive growth at above 25 °C for the cydippids. Moreover, cydippids were strongly influenced by all the three stages of the copepod Acartia tonsa (nauplius, copepodite and adult), especially its later developmental stages. Due to the presence of M. leidyi, the maximum zooplankton abundance has shifted to cold seasons. There was also a relationship between M. leidyi with barnacle larvae and rotifers in the cold seasons. The interrelationships among the life stages of M. leidyi, particularly between the transition and cydippid, was a major factor in its population dynamics. The relationship curves between these environmental parameters and the life stages of M. leidyi were nonlinear and mostly sigmoidal (not absolutely linear). The magnitude of parameter importance and relationships curves varied with season and life stage.

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 million years 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.

The sessile barnacle Xenobalanus globicipitis was observed on multiple cetacean species during field surveys off the northern coast of Sao Paulo state, Brazil. However, the occurrence of X. globici...

The study of epibiont communities living on sea turtles could be considered as a low-cost approach to provide valuable insights into the habitat use and immigration behavior of these threatened marine reptiles. It has been, however, neglected in many regions. We examined epibiont assemblages of 46 hawksbill turtles (Eretmochelys imbricata) from two relatively distinct nesting sites in the Persian Gulf. These include 28 turtles from Dayyer-Nakhiloo National Park (DNNP) at the northern Gulf characterized by the Gulf environmental extremes (high salinities and wide-ranging temperatures), and 18 turtles from the Shibderaz beach at the Strait of Hormuz with a more moderate environment exposed by incoming currents from the Gulf of Oman. A total of 54 epibiont taxa were identified on the body surface of the turtles, 46 taxa from Shibderaz and 29 taxa from DNNP. Two barnacle species, Chelonibia testudinaria and Platylepas hexastylos, along with harpacticoid copepods and Rotaliid foraminifers were the most frequent epibionts, observed on almost all examined turtles. Harpacticoids were the most abundant epizoic taxa by the number (19.55 ± 3.9 ind.9 cm-2) followed by forams (Quinqueloculina spp.: 6.25 ± 1.5 and Rotaliids: 6.02 ± 1.3 ind.9 cm-2). Our results showed that the composition and structure of turtle epibionts in the two studied sites were significantly different with higher diversity at Shibderaz. We speculate that the difference is largely driven by their environmental conditions they live in. These baseline data are critical to adopt proper conservation and management strategies for this species in the harsh environment of the Gulf especially in the course of climate change. The data can further be used in regular monitoring studies to track ecological changes in this anthropogenically-impacted water body.

Movement is a fundamental characteristic of life, yet some invertebrate taxa, such as barnacles, permanently affix to a substratum as adults. Adult barnacles became ‘sessile’ over 500 Ma; however, we confirm that the epizoic sea turtle barnacle, Chelonibia testudinaria , has evolved the capacity for self-directed locomotion as adults. We also assess how these movements are affected by water currents and the distance between conspecifics. Finally, we microscopically examine the barnacle cement. Chelonibia testudinaria moved distances up to 78.6 mm yr −1 on loggerhead and green sea turtle hosts. Movements on live hosts and on acrylic panels occasionally involved abrupt course alterations of up to 90°. Our findings showed that barnacles tended to move directly against water flow and independent of nearby conspecifics. This suggests that these movements are not passively driven by external forces and instead are behaviourally directed. In addition, it indicates that these movements function primarily to facilitate feeding, not reproduction. While the mechanism enabling movement remained elusive, we observed that trails of cement bore signs of multi-layered, episodic secretion. We speculate that proximal causes of movement involve one or a combination of rapid shell growth, cement secretion coordinated with basal membrane lifting, and directed contraction of basal perimeter muscles.

Environmental controls on the biogeographic distribution of species are becoming increasingly relevant under the present climate change conditions. The reproductive cycle of the acorn barnacle Semibalanus balanoides at its southernmost European distribution limit in Galicia (Northwest Iberian Peninsula) was studied in two locations (42.57°N 8.96°W, 42.61°N 8.89°W) with different temperatures during a 4-year time series (2012–2016), where an isolated population breeds even though the temperature thresholds documented for northern populations of the species are exceeded. Ovary production, total number of embryos and pre-hatching developmental stage were significantly higher in the colder location than in the warmer one. Fecundity was higher in colder reproductive seasons mediated by upwelling regime and food supply 3 months prior to fertilization. Investment in ovary tissue was favored by high temperatures and food availability, whereas suspended sediment was negatively correlated with investment in ovary tissue. Larvae release was associated with high temperatures and suspended sediment. Phenology of reproductive events was similar to what was described in farther north populations. Results indicated that reproductive output of the species at its southernmost European distribution limit is comparable to that reported in northern latitudes and suggest adaptation or acclimatization to local environmental conditions as maturation of gonads and fertilization was successfully carried out at higher temperatures than documented in northern European populations.

Limpets and barnacles are important components of intertidal assemblages worldwide. This study examines the effects of barnacles on the foraging behaviour of the limpetPatella vulgata, which is the main algal grazer in the North-west Atlantic. The behaviour of limpets on a vertical seawall on the Isle of Man (UK) was investigated using autonomous radio-telemetry, comparing their activity patterns on plots characterized by dense barnacle cover and plots from which the barnacles had been removed. Limpet behaviour was investigated at mid-shore level, but two different elevations were considered. This experiment revealed a significant effect of barnacle cover on the activity ofP. vulgata. Limpets on smooth surfaces spent a greater proportion of total time active than did limpets on barnacles. Movement activity was also greater in areas that were lower down in the tidal range. In general, limpets were either predominantly active during diurnal high or nocturnal low tides and always avoided nocturnal high tides. Individuals on barnacles at the higher elevation concentrated their activity during nocturnal low water. All the other groups of limpets (smooth surfaces on the upper level and all individuals on the lower shore) had more excursions centred around daylight hours with an equal distribution of activity between periods of low and high water. Inter-individual variability was, however, pronounced.

Waterfowl occupied the prominent rating with respect to abundance among the birds on the Dolgiy Island in the south-eastern part of the Barents Sea in land habitats and coastal water habitats. Comparison of the number of clutches and broods of waterfowl per 10 km of walking trails in different years on the island shows that in recent years (2014, 2016 and 2017), compared to 2004, there was an increase in abundance of the breeding populations of the Barnacle Goose, the White-fronted Goose, the Bean Goose, the Long-tailed Duck and the King Eider. There was a particularly rapid growth in the abundance of the Barnacle Goose for the studied period which, in the land habitats of the island, occupied a leading position in terms of abundance among other geese. An increased abundance of the Barnacle Goose on the island was accompanied by changes in its choice of nesting habitat type and its distribution in the parental care and moulting periods. The results of our study show that with an increase in the nesting density of the Barnacle Goose, the similarity of its nesting habitat types with those of the White-fronted Goose also increased. Some links between the abundance of clutches and broods of waterfowl and weather parameters were observed in different years. The abundance of waterfowl clutches and broods on the island was highest in 2016, which was characterised by the highest average monthly temperature of June and the longest frost-free period for all the years of observation.

Annually, shipworms and other biofouling species cause millions of dollars in damage to wooden marine infrastructure across the world. Given their abundant larval supply and high dispersal potential, bioeroders and biofoulers are ubiquitous threats that shorten the lifespan of wooden docks, piers, boats and shoreline stabilization structures in coastal environments. Despite these impacts, there are no treatments that completely protect wood against shipworms and biofouling. To explore potential approaches for extending the lifespan of wooden shoreline stabilization structures, we conducted two field experiments to evaluate the resistance to shipworms and biofouling of small and large diameter branches of four trees – laurel oak (Quercus hemisphaerica), sweetgum (Liquidambar styraciflua), crepe myrtle (Lagerstroemia spp.), and black mangrove (Avicennia germinans) – positioned at varying distances from the sediment surface in southeastern US estuaries. We discovered that the wood volume lost to shipworm burrows was concentrated near the sediment surface, more prevalent in tree species with lower wood densities, and varied markedly between years. Barnacle fouling was far higher on branches > 30 cm from the surface and on laurel oak and sweetgum branches. In a third field experiment, we tested two chemical and two non-chemical wood treatments and found chemical treatments to be more effective at deterring barnacle fouling and shipworm burrowing of wooden posts, especially beneath the sediment surface. By identifying desirable characteristics of the wood employed and elevations at which the impacts of shipworms and biofouling are especially prevalent, this experimental study informs the design of more durable wooden stabilization structures in coastal environments.

Ten blue swimming crabs Portunus segnis (Forskal, 1775) were collected from the north west of the Arabian Gulf off the Iraqi marine waters from October to November 2017 at 29ᵒ 37′ N to 48ᵒ 47′ E. The barnacle Octolasmis angulata (Aurivillius, 1894) was found on the gills of the present species of crab, the mean incidence of infestation was 30%, while the mean Intensity of infestation was 12.3. The barnacle have a long and slim shaped calcareous plate with the presence of carina and the absence of tergum, in addition to the elongated shape of carina and scutum. The current study represents the first record of the barnacle O. angulata in the Arabian Gulf.

Pelagic larvae of benthic organisms comprise a substantial part of the coastal Arctic zooplankton community in spring–summer. We studied the timing, growth, and pelagic duration of Cirripedia larvae in Adventfjorden, a high-Arctic fjord in Spitsbergen, Svalbard. Two distinct abundance peaks were found: one in early May (~ 25.000 ind. m−3) and another one in late May (~ 35,580 ind m−3). DNA barcoding based on the COI gene was used to identify the barnacle larvae to species. Whereas both Balanus balanus and Semibalanus balanoides were present, the first one dominated (50–100%) the barnacle abundance. High resolution sampling and size measurements of Cirripedia larvae revealed that these larvae most likely originated from a single spawning event. Development of the larvae suggested a pelagic residence time of roughly 2 months for B. balanus and at least 1 month for S. balanoides in the Arctic. Long pelagic residence time, large potential for biofouling on ships and larger plastic debris, combined with the disappearance of landfast sea ice and less ice scouring opens up new opportunities for barnacles to colonize the high-Arctic littoral zone. In a future warmer Arctic, we therefore expect establishment of new, more temperate Cirripedia species in Svalbard.

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.

Understanding the movement behaviour of marine megafauna within and between habitats is valuable for informing conservation management, particularly for threatened species. Stable isotope analyses of soft-tissues have been used to understand these parameters in sea turtles, usually relying on concurrent satellite telemetry at high cost. Barnacles that grow on sea turtles have been shown to offer a source of isotopic history that reflects the temperature and salinity of the water in which the host animal has been. We used a novel method that combines barnacle growth rates and stable isotope analysis of barnacle shells (δ18O and δ13C) as predictors of home area for foraging sea turtles. We showed high success rates in assigning turtles to foraging areas in Queensland, Australia, based on isotope ratios from the shells of the barnacles that were attached to them (86–94% when areas were separated by >400 km). This method could be used to understand foraging distribution, migration distances and the habitat use of nesting turtles throughout the world, benefiting conservation and management of these threatened species and may be applied to other taxa that carry hitchhiking barnacles through oceans or estuaries.

In Greenland, tidewater glaciers discharge turbid subglacial freshwater into fjords, forming plumes near the calving fronts. To evaluate the effects of this discharge on the zooplankton community in the fjords, we collected sea surface zooplankton samples in Bowdoin Fjord in north-western Greenland during the summer of 2016 and made microscopic, OPC and ZooScan analyses. Within the three quantitative methods, ZooScan has advantages that can evaluate various parameters (e.g., abundance, biomass, size and taxonomic information) simultaneously and has the ability to eliminate abiotic particles, such as silt and sediment, which are abundant in samples. Based on taxonomic biomass data, the zooplankton community is clustered into three groups, which varied spatially: inner, middle and outer fjord groups. Jellyfish dominated the outer fjord group, and barnacle cypris larvae dominated the middle fjord group. For the inner fjord group, large-sized Calanus spp. and chaetognaths were abundant. Since these species are characterized with oceanic taxa, they would intrude through the deep fjord water and subsequently be upwelled through entrainment of glacially modified plume water. From the NBSS analysis on zooplankton size spectra, the steep slope of NBSS in the middle fjord community suggests that the high productivity was caused by the addition of meroplanktonic cypris larvae.

Quantifying scale-dependent patterns and linking ecological to environmental variation is required to understand mechanisms regulating biodiversity. We conducted a large-scale survey in rocky shores along the SE Brazilian coast to examine spatial variability in body size and density of an intertidal barnacle (Chthamalus bisinuatus) and its relationships with benthic and oceanographic predictors. Both the size and density of barnacles showed most variation at the smallest spatial scales. On average, barnacle body size was larger on shores located in areas characterised by higher chlorophyll levels, colder waters, low wave action and low influence of freshwater. Barnacles were more abundant at wave-exposed shores. We identified critical scales of spatial variation of an important species and linked population patterns to essential environmental predictors. Our results show that populations of this barnacle are coupled to scale-dependent oceanographic variation. This study offers insights into the mechanisms regulating coastal populations along a little studied coastline.

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 naive 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.

The present work studied the diversity of intertidal, epibiotic, and fouling barnacles in the state of Gujarat, northwest India. In total, eleven species belonging to eight genera and five families were recorded in the present study. The Arabian intertidal species Tetraclita ehsani Shahdadi, Chan & Sari, 2011 and Chthamalus barnesi Achituv & Safriel, 1980 are common in the high- and mid-intertidal rocky shores of Gujarat suggesting that the Gujarat barnacle assemblages are similar to the assemblages in the Gulf of Oman Ecoregion. The biogeographical boundary between the Gulf of Oman and Western Indian ecoregions for barnacles should probably extend southward towards the waters adjacent to Mumbai, where Indo-Pacific species of intertidal barnacles dominate. This study provides the first reports of the common widely distributed balanomorph barnacles Striatobalanus tenuis (Hoek, 1883), Tetraclitella karandei Ross, 1971, Amphibalanus reticulatus (Utinomi, 1967), and lepadid barnacle Lepas anatifera Linnaeus, 1758 in Gujarat, as well as of the chthamalid barnacle Chthamalus barnesi in India.

Systematic overview of the molluscan and barnacle assemblages of the Pliocene Tjornes sequence in North Iceland is primarily based on collections and fieldwork carried out during the last 50 years and collections of the Institute of Natural History in Reykjavik, the Geological Museum in Copenhagen, and the collection of the late farmer Johannes Bjornsson in Ytri-Tunga on Tjornes. We have identified 65 species of prosobranch gastropods, five opistobranch gastropod, 49 bivalve, one ammonite, and one barnacle species. Of the 119 molluscan species, 24 have not been recorded before from Tjornes. About 25% of the mollusc species are extinct, and 25 of the recent molluscan species now live in southerly localities with higher sea temperatures. At least 32 of the species have their first appearance (FAD) in Tjornes. The species are depicted on plates and variation in shape is demonstrated wherever possible. The distribution, recent or fossil, of species is shown, and ecological and biological features discussed. The larval development of the species is also summarized. The Tjornes fauna is major record of trans-Arctic oceanic interchange that has been imperative in shaping the modern North Atlantic faunas. This review enables us to improve our understanding of the interchange.

Distribution patterns in the upper intertidal zone, where diversity is low, are often explained by the variation in physical factors. However, certain environmental conditions may hinder resource monopolization by a dominant species, allowing for the coexistence of species. Under these conditions, interspecific interactions may become relevant. In southeastern Brazil, the upper intertidal zone of exposed rocky shores is typically colonized by the barnacle Chthamalus bisinuatus. In estuaries, two other species, Chthamalus proteus and Microeuraphia rhizophorae, may occur on hard substrates, although patterns of coexistence at relevant spatial scales are presently unknown, which prevents a better understanding of the ecology of rocky shore systems in the region. This study aimed to (i) describe the distribution patterns of chthamalid barnacles along the Paranagua Estuarine Complex (PEC) and (ii) evaluate the vertical distribution of species in places where substantial coexistence was observed to preliminarily test whether their distribution is compatible with a lottery model of resource acquisition or compatible with a process of interspecific interference competition. A well-defined barnacle community was observed along the upper intertidal zone, from the euhaline to the oligohaline sector, with the cover area being larger in the euhaline sector. The effects of hydrodynamic exposure were limited to the euhaline sector, where barnacles covered larger extensions of the rocky intertidal habitat at more exposed sites. Barnacle density did not vary consistently among sectors or levels of hydrodynamic exposure but changed according to certain combinations of these factors. As a result, the realized habitat tended to decrease from the mouth of the estuary to the oligohaline sector. Three species were recorded in this study: Chthamalus bisinuatus, practically limited to the euhaline sector; Microeuraphia rhizophorae, limited to the polyhaline and mesohaline sectors; and Chthamalus proteus, limited to the polyhaline, mesohaline and oligohaline sectors. Habitat sharing was substantial only in 3 of the 16 sampled sites and only between Microeuraphia rhizophorae and Chthamalus proteus. At low barnacle densities, up to 40% substrate cover, there was no apparent vertical segregation between these two species. Above 40–50% cover, Microeuraphia rhizophorae occupied a higher position on the shore than Chthamalus proteus. These results suggest a lottery model when vacant space is still abundant and interspecific interference competition when barnacle abundance surpasses a critical abundance threshold. In this latter case, Chthamalus proteus displaces Microeuraphia rhizophorae to upper zone levels, where conditions for growth and reproduction are probably less favorable.

Barnacles are the epitome of a sessile animal, so it seems incongruous that some are among the widest-roving invertebrates on the planet, maybe beyond even what Mr. Quammen has conceived. All members of the barnacle superfamily Coronuloidea have acquired the borrowed ability to travel many hundreds, or thousands of kilometers over a lifetime as epibionts of their mobile hosts or basibionts. These epizoites of sea turtles, sea snakes, crabs, whales, and other mobile fauna (Darwin 1854; Zann 1975; Hayashi 2013a), utilize their live substratum as a platform for feeding and dispersal, but not as a source of nutrition. The greatest number specializes on sea turtles but their host repertoires and specificity for particular turtle species have not previously been rigorously evaluated. I endeavor to fill this gap to gain greater understanding of these associations and insight on how barnacles select a mobile home. The nature of barnacle–turtle relationships falls somewhere between parasitism and mutualism. Not a phoretic symbiosis, whereby one animal attaches to another temporarily for conveyance (White et al. 2017), the association is most frequently considered a commensalism. The term refers to feeding at a common table (van Beneden 1876) and results in the commensal deriving benefit from the arrangement while the host remains unaffected. However, the view that turtle hosts are not negatively affected by barnacles is, depending on the situation and the symbiont involved, often plausible, in some cases debatable, and occasionally untenable. Commensalisms are rarely demonstrated as obligate and specific (Wahl and Mark 1999) and many are not stable, tipping toward the benefit or detriment of the host depending on circumstances; indeed, the argument has been made that the concept of commensalism, in the narrow sense, is a theoretical state that cannot be empirically demonstrated (Zapalski 2011). Thus, multiple states apply for epizoic barnacles. Whatever the designation, advantages certainly accrue to barnacles by living on mobile hosts, including access to reliable currents for passive feeding and protection from benthic predators (Foster 1987). The obligate nature of coronuloid barnacles on their hosts, especially as associates of whales and turtles (Scarff 1986; Hayashi 2013a), is well-demonstrated, with several taxa known from only a single species of cetacean or chelonian (Marloth 1900; Monroe and Limpus 1979). Of the more than 200 species of epibionts documented from sea turtles (Frick and Pfaller 2013), most are facultative associates, but barnacles are the most common obligate taxa. Yet, despite their affinity for sea turtles, a one barnacle–one turtle paradigm is likely the exception rather than the rule. For example, the common “turtle” barnacle, Chelonibia testudinaria (Fig. 1A), has the most elastic host use, regularly utilizing manatees, various crabs, and all species of sea turtles as basibionts (Zardus et al. 2014) and exceptionally, other kinds of reptiles and crustaceans (Ross and Jackson 1972; Badrudeen 2000; Ortiz et al. 2004; Nifong and Frick 2011), even various synthetic substrata (Edmondson and Ingram 1939; Frazier and Margaritoulis 1990; Sloan et al. 2014). Lacking an all-encompassing label to describe the relationship of barnacles with sea turtles, it is perhaps most easily summarized as an obligate association of generally intermediate specificity with neutral to negative consequences for the host. Open in a separate window Fig. 1 Barnacle exemplars that attach to sea turtles by: (A) cementing, Chelonibia testudinaria; (B) clinging, Platyleaps hexastylos; (C); embedding, Stomatolepas elegans [the shell is right side up!]; (D) penetrating, Stephanolepas muricata; and (E) boring, Chelolepas cheloniae (scale bars = 5 mm).

This chapter deals with the systematic aspects of the molluscan and barnacle assemblages found in the Breiðavik Group in North Iceland. They are primarily based on collections and field work carried out more or less each year since 1972. They are also based on the collections of the Institute of Natural History (Museum) in Reykjavik, the Geological Museum in Copenhagen, the collection of the farmer Johannes Bjornsson in Ytri-Tunga on Tjornes, and the collection of Mar Vilhjalmsson in Icelandic Institute of Natural History. We report 14 species of prosobranch gastropods, 2 opisthobranch gastropod species, 29 species of bivalves, and 2 species of barnacles have been identified from the Breiðavik Group. In total, it is a question of 45 species of molluscs and 2 barnacle species. Two of the mollusc species are new for the Breiðavik Group. Each species is illustrated on plates, and variation in shape is demonstrated where the material makes it possible. The distribution, recent or fossil, of the various species is recorded, and pertinent ecological and biological features are discussed. The larval development of the species is also recorded as their ability to migrate is significantly depending on the pelagic larval development. The Early Pleistocene Breiðavik fauna marks the transition of the warm temperate Tjornes faunas to the subarctic-arctic faunas at the onset of the Pleistocene.

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. publishedVersion

The transition of planktonic late-stage barnacle larvae to a benthic life requires enough energy to power settlement and metamorphosis, and may be compromised by food limitation during early ontogeny. We carried out a comparative study to better understand the larval physiology of space-monopolizing barnacles exposed to contrasting regimes of primary productivity:Chthamalus bisinuatusunder a meso-oligotrophic regime on the southeastern coast of Brazil, andC. montaguiunder a highly productive regime on the southwestern coast of the British Isles. We used an index based on lipid composition—the triacylglycerol (TAG) to phospholipid (PL) ratio—to characterize lipid allocation (energy/structure) in the tissues of cyprid larvae and anticipated depleted TAG reserves in cyprids from less productive waters. Despite the considerably different levels of primary productivity between subtropical (1.31 ± 0.4 mg chlam-3) and temperate waters (3.09 ± 1.2 mg chlam-3), TAG/PL ratio and settlement success were comparable forC. bisinuatusandC. montagui. Lipid allocation of daily cohorts was also comparable for both chthamalids, with cyprids equally storing TAG reserves (≥50% of total lipid content). This points to an energetic threshold below which nauplii cannot develop to a cyprid and/or selection for lipid accumulation under poor trophic conditions. We highlight the challenges of directly relating estimates of primary productivity with food supply and larval physiological status, as lower chlaconcentrations do not necessarily indicate food limitation for barnacle nauplii. We propose a conceptual model to clarify the process of lipid allocation (energetic to structural lipids) in the tissues of cyprid larvae.

The intertidal zone is characterized by persistent, tidally-driven fluctuations in both abiotic (e.g., temperature, oxygen, and salinity) and biotic (e.g., food availability and predation) factors, which make this a physiologically challenging habitat for resident organisms. The relative magnitude and degree of variability of environmental stress differ between intertidal zones, with the most extreme physiological stress often being experienced by organisms in the high intertidal. Given that so many of the constantly shifting parameters in this habitat are primary drivers of metabolic rate (e.g., temperature, [O2], and food availability), we hypothesized that sessile conspecifics residing in different tidal zones would exhibit distinct “metabolic phenotypes,” a term we use to collectively describe the organisms’ baseline metabolic performance and capacity. To investigate this hypothesis, we collected acorn barnacles (Balanus glandula) from low, mid, and high intertidal positions in San Luis Obispo Bay, CA, and measured a suite of biochemical (whole-animal citrate synthase (CS) and lactate dehydrogenase (LDH) activity, and aerial [D-lactate]), physiological (O2 consumption rates), morphological (body size), and behavioral (e.g., cirri beat frequency and percentage of time operculum open) indices of metabolism. We found tidal zone-dependent differences in B. glandula metabolism that primarily related to anaerobic capacity, cirral activity patterns, and body size. Barnacles from the low intertidal tended to have a greater capacity for anaerobic metabolism (i.e., increased LDH activity and increased baseline [D-lactate]), have reduced cirral beating activity—and presumably reduced feeding—when submerged, and be smaller in size compared to conspecifics in the high intertidal. We did not, however, see any D-lactate accumulation in barnacles from any tidal height throughout 96 h of air exposure. This trend indicates that the enhanced capacity of low intertidal barnacles for anaerobic metabolism may have evolved to support metabolism during more prolonged episodes of emersion or during events other than emersion (e.g., coastal hypoxia and predation). There were also no significant differences in CS activity or baseline O2 consumption rates (in air or seawater at 14°C) across tidal heights, which imply that aerobic metabolic capacity may not be as sensitive to tidal position as anaerobic processes. Understanding how individuals occupying different shore heights differ in their metabolic capacity becomes increasingly interesting in the context of global climate change, given that the intertidal zone is predicted to experience even greater extremes in abiotic stress.

Among the turtle and whale barnacles (Coronuloidea: Chelonibiidae, Coronulidae, †Emersoni-idae and Platylepadidae), the members of the chelonibiid species Chelonibia testudinaria (Linnaeus, 1758) are known as epizoic barnacles that can attach to a rather wide spectrum of substrates (pri-marily sea turtles, crabs and sirenians). At present, three living morphs of C. testudinaria have been recognised; of these, the less host-specific is the patula morph, which also displays a remarkably simple, unspecialised shell architecture. Here we report on several chelonibiid shells, referred to the patula morph of C. testudinaria, encrusting a cetacean scapula collected from the floor of the Adriatic Sea facing Salento (Apulia Region, southeastern Italy) and tentatively referred to Tursiops truncatus (Montagu, 1821). This is one of the few records worldwide of a coronuloid barnacle from an inanimate substrate, as well as the second as an encruster on mammalian bone. Such an unusual occurrence is then briefly discussed in the broader framework of the coronuloid commensalism and substrate habits., Među kornjačama i kitovima (Coronuloidea: Chelonibiidae, Coronulidae, † Emersoniidae i Platylepadidae), pripadnici vrste Chelonibia testudinaria (Linnaeus, 1758) poznati su kao epizoični brumbuljci koji se mogu pričvrstiti na prilično širok spektar podloga (prvenstveno na kornjače, rakove i velike vodene sisavce koji se hrane biljkama iz reda Sirenia). Trenutno su prepoznata tri živa morfija C. testudinaria; od njih, manje specifična za domaćina je morph patula, koja također prikazuje izuzetno jednostavnu, nespecijaliziranu arhitekturu ljuske. U ovom radu izvještavamo o nekoliko ljuski helonibiida, koje se odnose na morfe patule C. tes-tudinaria, koja inkrustira lopaticu kitova sakupljenu s dna Jadranskog mora prema Salentu (regija Apulia, jugoistočna Italija) i okvirno upućenu na Tursiops truncatus (Montagu, 1821). Ovo je jedan od rijetkih zapisa u svijetu o brumbuljku iz nežive podloge, a i kao drugi slučaj inkrustriranja na kosti sisavca. Takva neobična pojava potom se ukratko raspravlja u širem kontekstu komensalizma brumbuljaka i supstrata staništa.

We investigated the spatial variation of molluscan assemblages with different habitat-forming species and bare rock habitat in a rocky intertidal zone in northeastern Brazil. The high intertidal zone substrate was covered predominantly of barnacles [Chthamalus bisinuatus (Pilsbry, 1916)], the mid-intertidal of mussels [Brachidontes exustus (Linnaeus, 1758)] and the low intertidal of macroalgae chlorophytes [Gayralia oxysperma (Kützing) K. L. Vinogradova ex Scagel et al., 1989 and Ulva lactuca Linnaeus, 1753], phaeophytes [Sargassum vulgare C. Agardh] and rhodophytes [Palisada flagellifera (J.Agardh) K. W. Nam, 2007]. A total of 3,861 mollusks were recorded, belonging to the classes Gastropoda (9 species; 3,800 individuals), Bivalvia (3 spp.; 54 ind.), and Polyplacophora (1 sp.; 7 ind.). Functional diversity was accessed through the trophic structure, in which we identified food guilds: suspension feeders, grazers, herbivores, and carnivores. The analysis revealed significant differences in mollusk abundance, species richness, diversity indices, and trophic diversity among barnacle belts, mussel beds, algae habitat, and bare rock habitats. The highest species richness and trophic diversity were detected in algae habitat and mussel beds, which showed low abundance. In contrast, barnacle belts registered low species richness and trophic diversity and a high number of individuals. Bare rock recorded low values in all surveyed indices. This result points to the effect of environmental modification caused by habitat-forming species in this system. These species increase environmental complexity and enable the establishment of organisms through facilitation processes. The various food guilds found in this study reaffirm the role of habitat-forming species in providing niches that support different occupation patterns. RESUMO Nós investigamos a variação espacial das assembleias de moluscos em função de diferentes habitats formados por fauna séssil e substrato rochoso em uma zona entre marés rochosa no nordeste do Brasil. O substrato da zona entre marés superior era predominantemente recoberto por cracas [Chthamalus bisinuatus (Pilsbry, 1916)], da zona entre marés média por mexilhões [Brachidontes exustus (Linnaeus, 1758)] e da zona entre marés inferior por macroalgas clorofíceas [Gayralia oxysperma (Kützing) K. L. Vinogradova ex Scagel et al., 1989 and Ulva lactuca Linnaeus, 1753], feofíceas [Sargassum vulgare C. Agardh, 1820] e rodofíceas [Palisada flagellifera (J. Agardh) K. W. Nam, 2007]. Foram registrados 3861 moluscos pertecentes às classes Gastropoda (9 espécies; 3800 indivíduos), Bivalvia (3 spp.; 54 ind.), e Polyplacophora (1 sp.; 7 ind.). A diversidade funcional foi analisada através da estrutura trófica, na qual identificamos as guildas alimentares: suspensívoros, raspadores, herbívoros e carnívoros. Abundância, riqueza de espécies, diversidade de Shannon, uniformidade de Pielou e diversidade trófica variaram em função dos habitats formados por cracas, mexilhões, algas e substrato rochoso. Habitats formados por algas e mexilhões apresentaram elevada riqueza de espécies e diversidade trófica, entretanto, apresentaram baixa abundância. Ao contrário, o habitat formado por cracas registrou baixa riqueza e diversidade trófica e elevado número de indivíduos. O substrato rochoso apresentou valores baixos em todos os índices investigados. Esse resultado mostra o efeito da modificação ambiental provocada pela fauna séssil nesse sistema. Esses organismos aumentam a complexidade ambiental e viabilizam o estabelecimento de organismos por meio de processos de facilitação. As diferentes guildas alimentares encontradas neste estudo reafirmam o papel dos substratos biológicos no fornecimento de nichos capazes de suportar diferentes padrões de ocupação.

Human growth has caused an unprecedented increase in artificial light at night (ALAN). In coastal habitats, many species rely on day/night cycles to regulate various aspects of their life history and these cycles can be altered by this stressor. This study assessed the influence of ALAN on the early (cyprid) and late (spat) settlement stages of the acorn barnacle Semibalanus balanoides, a species widely distributed in natural and man-made coastal habitats of the North Atlantic. A newly designed settlement plate, originally for studies in rocky intertidal habitats in the southeast Pacific, was adapted to measure settlement rates on man-made habitats -wharf seawalls- located in Atlantic Canada. Plates equipped with a small LED diode powered by an internal battery (ALAN plates) were used to quantify settlement rates in comparison to plates lacking a light source (controls). These plates were deployed for 6 d in the mid-intertidal levels, where adult barnacles were readily visible. ALAN and control plates collected large number of settlers and showed to be suitable for this type of man-made habitats. The number of early settlers (cyprids) did not differ between plates but the number of late settlers (spat) was significantly lower in ALAN plates than in controls. These results suggest that light pollution has little influence on the early stages of the acorn barnacle settlement but is clearly detrimental to its late stages. As barnacles dominate in many natural and man-made hard substrates, it is likely that ALAN also has indirect effects on community structure.

Climate change has already altered the environmental conditions of the world’s oceans. Here we report declines in gastropod abundances and recruitment of mussels (Mytilus edulis) and barnacles (Semibalanus balanoides) over the last two decades that are correlated with changes in temperature and ocean conditions. Mussel recruitment is declining by 15.7% per year, barnacle recruitment by 5.0% per year, and abundances of three common gastropods are declining by an average of 3.1% per year (Testudinalia testudinalis, Littorina littorea, and Nucella lapillus). The declines in mussels and the common periwinkle (L. littorea) are correlated with warming sea temperatures and the declines in T. testudinalis and N. lapillus are correlated with aragonite saturation state, which affects rates of shell calcification. These species are common on shores throughout the North Atlantic and their loss is likely to lead to simplification of an important food web on rocky shores., Petraitis and Dudgeon report a decline in mussel and gastropod abundance and recruitment on rocky intertidal shores of the Gulf of Maine over a period of 20 years. These declines are correlated with increased water temperatures and aragonite saturation state, which affects rates of shell calcification, and suggests environmental impacts on the food webs of rocky shores.

Dozens of samples of stalked barnacles were collected from deep-sea seamounts of the tropical western Pacific by remotely operated vehicles during two expeditions in 2017 and 2018. Integrative taxonomy indicates that they represent two new species belonging to the families Scalpellidae and Poecilasmatidae, respectively. In terms of morphology, Arcoscalpellum angularum sp. nov. is distinguished from congeneric species by the angular processes on the dorsum of its soft body and the absence of a caudal appendage, whereas Glyptelasma robustum sp. nov. differs from its congeners in its robust peduncle, semicircular concaved carina, and long filamentary appendages. The validity of the two new species is supported by genetic analyses inferred from COI gene sequences and geographic distribution. To date, very few seamounts in the oceans have been investigated for scientific purposes, and little is known about the barnacles that inhabit these seamounts. A literature search reveals about 112 barnacle species recorded in seamounts mainly in the eastern and western regions of the Pacific Ocean. Existing data are insufficient for research on species speciation and diffusion; still more credible data on the distribution of barnacles in seamounts should be collected.

Predation is one of the driving forces that shaped the marine ecosystems through time. Apart from the anti-predatory strategies adopted by the prey, the predatory outcome is often indirectly influenced by the other members of the ecological community. Association between organisms are often found to influence the outcome and the evolution of such association may have been guided by such interactions. Mollusc-burnacle association, although common, is not explored to assess if the epibiont offers the molluscs any protection against predation (associational resistance) or increases the risk by attracting predators (shared doom). Using a series of controlled experiments with a drilling predator (Paratectonatica tigrina), its prey (Pirenella cingulata) and an epibiont (Amphibalanus amphitrite), we evaluated the effect of epibionts on the drilling behavior of the predator by documenting the successful attack (Drilling frequency, DF), and handling time. Our results show that the prey with epibionts are significantly less likely to be drilled when the predator has sufficient choice of prey, consistent with the tenets of the associational resistance. The preference of choosing the non-encrusted prey, however, diminishes with fewer available prey. The handling time is significantly higher in the attacks on the encrusted prey than non-encrusted prey, even though the barnacles are not drilled. Although the proximity of the drilling site to encrustation tends to increase the handling time, the size of encrustation does not have any effect. Because the profitability of prey largely depends on the ratio of handling time and the energetic yield from consuming the prey, the increase in handling time due to encrustation makes it less profitable for the predator. The role of encrustation as a deterrent to predation might also explain the complex shell architecture in some prey gastropods that increases the likelihood of encrustation besides providing direct resistance against predation.

The population of barnacle geese wintering in Denmark has shown a steep increase during the last decades, prompting a parallel escalation of agricultural conflicts. In Denmark, economic compensation to farmers suffering goose damage to crops is not practiced, but despite that the barnacle goose is fully protected, landowners can obtain a permit to undertake so-called derogation shooting (lethal scaring) to reduce local damage to agricultural crops where other means of scaring have been insufficient. Here, we describe the development in numbers and derogation efforts of barnacle geese in Denmark in the period 2010/11 – 2018/19. We demonstrate that differences in the number of issued derogation permits across the country is primarily explained by differences in barnacle goose abundance, and secondarily, by prevalence of vulnerable crops and differences in crop productivity. Hence, derogation efforts are highest in areas with many geese, high proportions of crops vulnerable to goose grazing and high crop yields. Our analysis indicates that the level of conflict, and probably the economic impact of affected farmers, is proportional to the abundance of geese present locally. While the increasing derogation shooting may be a temporary solution to individual farmers, current unorganised practice might only redistribute geese locally and increase energy demands of the affected birds. Currently, there is a lack of alternative and undisturbed accommodation areas in the Danish agricultural landscape for the displacement of geese to achieve a satisfactory effect of derogation shooting.

The rocky intertidal zone has a long history of ecological study with barnacles frequently serving as a model system to explore foundational theories. Parasites are often ignored in community ecology studies, and this particularly holds for true for the rocky intertidal zone. We explore the role of the isopod parasite,Hemioniscus balani, on its host, the acorn barnacle,Chthamalus fissus.We use the currencies of biomass and reproduction measured at the individual level, then applied to the population level, to evaluate the importance of this parasite to barnacle populations. We foundH. balanican comprise substantial biomass in ‘apparent’ barnacle populations, sometimes even equaling barnacle biomass. Additionally, parasite reproduction sometimes matched barnacle reproduction. Thus, parasites divert substantial energy flow from the barnacle population and to near-shore communities in the form of parasite larvae. Parasites appeared to decrease barnacle reproduction per area. Potentially, this parasite may control barnacle populations, depending on the extent to which heavily infected barnacle populations contribute to barnacle populations at larger scales. These findings regarding the importance of a particular parasite for host population dynamics in this well studied ecosystem call for the integration of disease dynamics into community ecological studies of the rocky intertidal zone.

Coastal areas are critical transition zones between marine and terrestrial domains that support a large diversity of species but are exposed to significant anthropogenic impacts. While most conservation and management strategies rely on understanding the drivers of diversity over large scales, the importance of small-scale variation in environmental conditions can be overlooked. Here we combined a descriptive and experimental approach to describe the spatio-temporal dynamics of sessile communities and of the population of the barnacle Chthamalus bisinuatus within Araca Bay, a transition zone in southeastern Brazil threatened by the expansion of the Sao Sebastiao Port. We compared the relative coverage of sessile organisms from rocky shores for 20 months and several population parameters of barnacles in three distinct regions of Araca Bay, a few hundred meters apart: the inner portion, close to the Mae Isabel River and the Port, the middle of the Bay, and the outer region, close to the bay entrance. Community structure varied significantly over these small spatial scales; the macroalga Ulva lactuca and the oyster Crassostrea sp. were more abundant in the inner portion of the Bay, where the influence of freshwater and organic pollution from Mae Isabel River is more intense. Recruitment and density of C. bisinuatus was higher on the shores close to the mouth of the Bay, but individual size increased as one moves into the bay. Experimental manipulation of barnacles originally recruiting at the outer part of the bay and translocated to both outer and inner positions showed that while recruitment is restricted at the inner region, barnacle growth and survival are higher than at the outer shore. Our results suggest that the gradient of physical conditions created along the Araca Bay can result in distinct dynamics of communities and populations and that the region close to the mouth of the bay is more dynamic, with a larger turnover of space. In the opposite direction, the inner part of the bay, which is closer to the Sao Sebastiao Port, is more prone to be disturbed by any large human modification on the coast as populations are less dynamic and communities tend to be monopolized by species associated with organic pollution. Besides providing useful data for the management of Araca Bay, our results also show that small-scale variation of environmental conditions can contribute to create distinct dynamics of populations and communities and should be addressed in assessments of environmental impacts on the coast.

Sex can influence patterns of parasitism because males and females can differ in encounter with, and susceptibility to, parasites. We investigate an isopod parasite (Hemioniscus balani) that consumes ovarian fluid, blocking female function of its barnacle host, a simultaneous hermaphrodite. As a hermaphrodite, sex is fluid, and individuals may allocate energy differentially to male versus female reproduction. We predicted the relationship between barnacle size and female reproductive function influences the distribution of parasites within barnacle populations. We surveyed 12 populations spanning ~400 km of coastline of southern California and found intermediate-sized barnacles where most likely to be actively functioning as females. While it is unclear why larger individuals are less likely to be actively reproducing as females, we suggest this reduced likelihood is driven by increased investment in male reproductive effort at larger sizes. The female function-size relationship was mirrored by the relationship between size and parasitism. We suggest parasitism by Hemioniscus balani imposes a cost to female function, reinforcing the lack of investment in female function by the largest individuals. Within the subset of suitable (=female) hosts, infection probability increased with size. Hence, the distribution of female function, combined with selection for larger hosts, primarily dictated patterns of infection.

A large number of specimens (2765) of the acorn barnacle Balanus trigonus Darwin, 1854, were observed on the spiny lobster Panulirus gracilis Streets, 1871, in western Mexico, including recently settled cypris (1019 individuals or 37%) and encrusted specimens (1746) of different sizes: 2.82 mm, 4%). Cypris settled predominantly on the carapace (67%), mostly on the gastric area (40%), on the left or right orbital areas (35%), on the head appendages, and on the pereiopods 103. Encrusting individuals were mostly small (84%); medium0sized specimens accounted for 11% and large for 5%. On the cephalothorax, most were observed in branchial (661) and orbital areas (240). Only 40-41 individuals were found on gastric and cardiac areas. Some individuals (246), mostly small (95%), were observed on the dorsal portion of somites. Of the encrusting individuals, 18% were dead with no clear pattern in localization, but less common (7%) on dorsal than on lateral portions (right, 18%; left, 32%). Larger specimens (up to 11 mm) were observed in other lobsters from different catches. Previous presence of Cirripedia in decapod crustaceans, size range in the material examined, settlement patterns, and growth of the barnacles are discussed.