Effects of prey escape ability,flow speed,and predator feeding mode on zooplankton capture by barnacles

Experimental studies of feeding on zooplankton often involve the use of non-evasive Artemia spp. to represent zooplanktonic prey. Some zooplankton, however, such as copepods, are potentially evasive due to possession of effective predator-avoidance mechanisms such as high-speed escape swimming. In the present study, we compared the efficiencies with which non-evasive (A. salina) and evasive (copepods) zooplankton were captured by a sessile, suspension feeder, the coral-inhabiting barnacle Nobia grandis (Crustacea, Cirripedia). N. grandis specimens and zooplankton used in the present study were collected near Eilat, Israel in 1993. The effect of different flow speeds (from 0 to 14 cm s^-1) on captures of the two preys was also investigated. Additionally, we examined the effect of a flow-induced barnacle behavioral switch from active to passive suspension feeding, on zooplankton capture. Two video cameras were used to make close-up, three dimensional recordings of predator-prey encounters in a computer-controlled flow tank. Frame-by-frame video analysis revealed a highly significant difference (P< 0.001) in the efficiency with which A. salina and copepods were caught (A. salina being much more readily captured than copepods). After an encounter with cirri of feeding barnacles, copepods were usually able to swim out of the barnacles capture zone within one video frame (40 ms), by accelerating from a slow swimming speed (approximately 1.85 cm s^-1) to a mean escape swimming speed of 18.11 cm s^-1 (ca. 360 body lengths s^-1). This was not the case for A. salina nauplii, which usually remained in contact with cirri before being transferred to the mouth and ingested. Thus, experimental studies addressing the methodology of organisms feeding on zooplankton should consider that slow-swimming prey like Artemia sp. nauplii may only represent the non-evasive fraction of natural mesozooplankton assemblages.     

Hypoxic life of intertidal acorn barnacles

Oxygen levels were monitored within the mantle cavities of three barnacle species ( Chthamalus stellatus, Semibalanus balanoides, Elminius modestus), using optode microsensors. Conditions were always hypoxic, even when barnacles were actively using the prosoma and cirri to pump aerated seawater into the mantle cavity. Mantle fluid oxygen concentrations were extremely variable; behaviour and oxygen concentrations were not closely coupled. Ventilation of the mantle cavity depended partially on external water flow, with higher and more stable mantle fluid oxygen concentrations being sustained when the water around barnacles was agitated. During emersion, barnacles initially pumped seawater between the mantle cavity and the cone above the opercular plates to achieve ventilation. As water was lost it was replaced by air bubbles, eventually resulting in an air-filled mantle cavity. In S. balanoides and E. modestus, once the mantle cavity was filled with air, the barnacle usually used up the oxygen within the bubble within 2–3 h and did not regain oxic conditions until the barnacle was reimmersed in seawater. In C. stellatus, the air bubble was repeatedly refreshed for many hours by pneumostome formation. In response to low environmental salinity, all three species closed the opercular plates firmly and rapidly used up oxygen within the mantle fluid.     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

Inhibition of marine algal photosynthesis by heavy metals

The orientation of the opportunist, sublittoral barnacle Balanus trigonus is investigated. Water movement is the primary orientation stimulus for this species, but this effect may be modified by the influence of light acting in opposition to it. The barnacles orientate at right angles to the axis of wave-surge movement, and observations of feeding behaviour showed that in this position the cirral net could be swivelled 90° each way to make best use of both the advancing, and the reversing, water flow. In a steady unidirectional tidal current the barnacles aligned themselves so as to beat with the water flow, and observation suggests that stroking with the flow is more efficient than forcing the cirral net against the motion of the water. It is suggested that, for an opportunist short-lived species such as B. trigonus which is subjected to high predation rates, there is considerable selection pressure for rapid growth and early sexual maturity. To achieve this in a filterfeeding organism for which food is limiting, food collection must be as efficient as possible. B. trigonus has adopted a system of orientation to a variety of water movement regimes that allows efficient food collection over a wide range of conditions.     

Effects of simulated sublethal predation on the growth and regeneration rates of a spionid polychaete in laboratory flumes

Most spionid polychaetes switch from deposit feeding to suspension feeding as current speed and the flux of suspended food increase. Growth rates of juvenile Polydora cornuta are strongly affected by flow and can be as rapid as 60% day⁻¹ in moderate currents. Feeding palps that extend above the sediment–water interface during suspension feeding are especially vulnerable to sublethal predation, but individuals with damaged posteriors are also common. We performed a series of laboratory flume experiments to test the effects of sublethal tissue damage on the growth and regeneration rates of P. cornuta juveniles. Replicated experiments were conducted at three flow speeds in counter-rotating annular flumes containing field-collected sediment and a nonliving algal slurry as deposited and suspended food. In the first set of experiments, we removed 2, 1, or 0 of worms’ two feeding palps and measured the relative growth rates of worm bodies and palps after 3 days in the flumes. Worms that lost both palps grew significantly slower than the other two groups, but the growth rate of worms that had one undamaged palp was not significantly different from worms that had two undamaged palps. Faster flow speeds significantly increased rates of body growth, and there was a significant interaction between flow and the effect of palp loss. During the 3-day experiments, damaged palps fully regenerated and often grew larger than they were prior to being removed. Damaged palps also grew significantly faster than undamaged palps. The second set of experiments tested the effects of removing a worm’s posterior region (~18% of body volume). The growth rates of these damaged and undamaged worms did not differ significantly. By the end of a 3-day flume experiment, damaged worms had grown 6× larger than they were prior to the posterior damage. The rapid regeneration of damaged palps and posterior tissue in moderate flows that allow suspension feeding suggests that sublethal predation on spionids might be more frequent than previously estimated and will have little impact on the growth of juvenile recruits.     

Sponge-inhabiting barnacles on Red Sea coral reefs

In this study eight different species of barnacles were found within nine species of sponges from the Red Sea. This brings to 11 the number of sponge-symbiotic barnacles reported from the Red Sea, two of these are new Acasta species (not described herein) and one (A. tzetlini Kolbasov) is a new record for this sea. This number is much higher than that of symbiotic barnacles found within sponges from either the N. Atlantic (2) or the Mediterranean (4). Two possible explanations for this are the presence of numerous predators in coral reefs and scarcity of available substrate for settlement. These factors can lead to high incidence of symbiotic relationships. Of the nine sponge species, only one (Suberites cf. clavatus) had previously been known to contain barnacles. Even at the family level, this is the first record of symbiotic barnacles in two out of the seven sponge families (Latrunculiidae, Theonellidae). Our present findings strengthen the apparent rule that the wider the openings in a barnacle shell, the fewer the host taxa with which it will associate, usually from one or two closely related families, and the more frequent it will associate with elastic sponges. Most Neoacasta laevigata found on Carteriospongia foliascens were located on the same side as the sponge's ostia, i.e. facing the incoming water. This adaptation allows the barnacles to catch more suspended particles from the water, provides them with more oxygen and prevents their exposure to discharged sponge waste. The highest density of barnacles observed on one face of a “leaf ” (with ostia) was 0.389 barnacles cm⁻² (one barnacle per 2.57 cm²) and on average 0.181 ± 0.68, while the average on the other side was only 0.068 ± 0.52 barnacles cm⁻². As indicated by the Morisita index, these barnacles most frequently (58%, n = 12) had a clumped spatial distribution (while the rest were randomly distributed), as is to be expected from such sessile organisms with internal fertilization via copulation. The presence of N. laevigata induced the growth of secondary perpendicular projections of its host C. foliascens. Of the N. laevigata examined, 17% brooded 324 ± 41 embryos each, of 286 ± 17 μm total length; only 5.7% (n = 123) were found to be dead. Size distribution analysis of skeletal elements from dead barnacles showed them to be significantly larger than the skeletal elements of the population of live barnacles ( p < 0.05). Received: 26 June 1998 / Accepted: 1 December 1998     

Barnacle larvae actively select flow environments supporting post-settlement growth and survival

Many marine dispersive propagules select specific settlement sites based on a range of environmental cues. However, the link between larval choice and post-settlement growth and survival is still poorly understood. Here we show that cypris larvae of the barnacle Balanus improvisus actively reject surfaces exposed to local flow speeds exceeding 5-10 cm/s. Field experiments show that post-settlement growth and survival decline in freestream flows above 15 cm/s. Moreover, studies in flume flow at local speeds exceeding 10 cm/s reveal that early juveniles show reduced feeding rates caused by deformation of the cirral fan, reduced retention efficiency, and a decrease in time spent feeding. We conclude that cypris larvae actively reject flow environments that will be suboptimal for suspension feeding in the early post-settlement phase. Our study suggests that larval choice can be adaptively connected to a specific part of the life cycle, in this case the very sensitive time after metamorphosis.     

Resistance to crushing from wave-borne debris in the barnacleBalanus glandula

Barnacles of the same species (Balanus glandula) show differences both in shell morphology and in their ability to resist crushing from impact at two sites within 8 km of each other which differ in their natural exposure to wave-borne debris (Cattle Point and False Bay, San Juan Island, Washington, USA). In studies performed in 1987, barnacles with shells of a given base diameter at the site exposed to more impact (Cattle Point) were found to have smaller bodies, shorter and thicker shells, and a more protected placement of their opercular valves than barnacles at the protected site. When tested with a standard impact, barnacles from the exposed site were more resistant to crushing both on the first impact and (for those surviving that test) on a second impact 2 wk later. The morphological differences between the two populations may be due to a combination of different shell: body growth rate ratios at the two sites plus passive remodelling of the exposed barnacles by small impacts. The morphological changes at the exposed site, although gained passively, fortuitously provide improved performance in resisting crushing from impact.Sessile Cirripedes, partly from being attached to surfaces having very different characters, partly from undergoing a varying amount of disintegration, and partly from unknown innate causes, are extremely variable As whole groups of specimens often vary in exactly the same manner, it is not easy to exaggerate the difficulty of discriminating species and varieties.Darwin (1854)     

Variable feeding behavior in three species ofMacoma (Bivalvia: Tellinacea) as a response to water flow and sediment transport

Many species of tellinacean bivalves mainly deposit-feed but are also known to vary their feeding behavior in response to predation and to the availability of suspended organic matter relative to that of sedimentary organic matter. This study showed that three species of the Pacific genusMacoma (Macoma nasuta Conrad, 1937,Macoma secta Conrad, 1837, andMacoma inquinata Deshayes, 1855, from the San Juan Islands, Washington, USA) varied their deposit-feeding behavior in response to water flow near the sediment-water interface and to sediment transport. In the summers of 1987, 1988 and 1989, water velocity was varied in a large racetrack flume, in order to change both water velocity and bottom sediment transport. In quiet water, the inhalant siphon was protruded far from the siphon hole. As water velocity increased, with little or no sediment transport, the deposit-feeding radius decreased. Qualitative observations suggested that this was related to the drag on the siphon. InM. secta, the distance of siphon protrusion was not related to body size. Under conditions of higher near-bottom water velocity, combined with bottom sediment transport, some individuals ceased to deposit-feed, while others sustained feeding by ingesting sediment within the siphon hole, at least 1 cm beneath the sediment-water interface. These results suggest that hydrodynamic conditions are a major determinant of feeding behavior, and previous explanations of variable feeding behavior as a response to predation may have to be adjusted to accommodate this expanded set of responses.     

Barnacles: Possible indicators of zinc pollution?

Barnacles [Balanus balanoides (L.), Elminius modestus Darwin, Lepas anatifera (L.)] from several different sites were found to accumulate the heavy metal zinc. The majority of the zinc was deposited in the tissues associated with the gut, and the level of zinc in soft body tissue generally reflected well the level of zinc in the immediate sea-water environment. The zinc accumulated in the gut tissues was in the form of discrete granules, mainly within the parenchyma cells which surround the gut. These granules probably exist as an insoluble zinc salt. A comparison of the zinc level in barnacles with those recorded for some other marine organisms indicates the possible usefulness of barnacles as indicators of zinc pollution.     

<Emphasis Type="Italic">Semibalanus</Emphasis><Emphasis Type="Italic">balanoides</Emphasis> in winter and spring: larval concentration,settlement, and substrate occupancy

This study measured the progression from pelagic larvae to juvenile barnacles, and examined whether recruitment of barnacles, Semibalanus balanoides Linnaeus, at two intertidal sites in contrasting hydrodynamic regimes was determined by pre-settlement or post-settlement processes. The two sites were 1.5 km apart in the vicinity of Woods Hole, Mass., USA. Quantitative plankton samples were taken twice weekly from December 1997 to May 1998 at a nearby site as an estimate of nearshore larval abundance. The presence of S. balanoides nauplii was noted, and cyprids were enumerated and measured. Larval settlement at the two sites [Gansett Point, Buzzards Bay (GP) and Little Harbor, Vineyard Sound (LH)] was estimated from examination of replicate settlement plates exposed for 2 or 3 days throughout the settlement season, and from replicate plots on marked rock quadrats at each site. On both plates and rocks settled cyprids and metamorphs were enumerated. Space occupancy on unmanipulated rock quadrats by all stages from cyprids to adult barnacles was also examined. Settlement occurred from 2 January to 20 May, and major settlement peaks coincided with peaks in pelagic cyprid concentration at LH, but not at GP. Space occupied by juvenile barnacles was close to zero up until late February despite substantial settlement prior to that. At LH, juvenile barnacle cover was zero at the end of the observations; all settlement failed. Almost 100% of settled cyprids failed to metamorphose within 2 days from late January to late March. Then the proportion metamorphosing increased sharply coinciding with a sudden increase of 3°C in water temperature. Observed site differences in space occupancy by juvenile barnacles suggest that while cyprid supply is a necessary condition for barnacle settlement, other factors affecting metamorphosis of settled cyprids and early juvenile mortality determine recruitment.     

High intertidal community organization on a rocky headland in Maine,USA

A mosaic patchwork of the barnacle Balanus balanoides L., the mussel Mytilus edulis L., and the alga Fucus vesiculosus L. was found in the transitional region between the mid and high intertidal zones on a rocky headland on Mount Desert Island, Maine, USA. The development of the mosaic was observed by following recruitment and survival of B. balanoides in denuded patches located at the same tidal level along a 60 m stretch of shore. Barnacle recruitment was least under canopies of F. vesiculosus and greatest in open areas kept moist at low tide by surf. Barnacle survival after settlement was least under the F. vesiculosus canopy due to the whiplash effect of the algal fronds in the surf and greatest in open areas free from competition from mussels. In open areas, early mortality was correlated with settlement density. In areas of dense settlement (60 spat cm^-2) up to 90% mortality resulted within 5 months from crowding associated with growth. In older individuals crowding produced hummocks of elongated, weakly attached barnacles which were more prone to removal by surf than uncrowded barnacles. Mussels exerted competitive dominance over barnacles for space and the presence of mussel beds prevented further barnacle recruitment. Mussels suffered extensive mortality during winter storms when surf removed dense mats of weakly attached mussels. The patchy distribution of mussels and barnacles results from irregular rock substrata producing numerous environmental patches with respect to wave exposure and drainage at low tide, and from densitydependent mortality of both mussels and barnacles which creates patches of new colonizable space within each environmental patch.     

Function of the shell spine in the predaceous rocky intertidal snail Acanthina spirata (Prosobranchia: Muricacea)

Feeding observations revealed that Acanthina spirata (Blainville, 1832) uses the shell spine in a ramming and prying motion, resulting in the fracturing and/or forcing open of opercular plates in the barnacles Balanus glandula (Darwin, 1854) and Chthamalus fissus (Darwin, 1854). Attacking barnacles by using the shell spine may represent a second widespread feeding mechanism (in addition to drilling) in muricacean gastropods. Specialization of the shell spine for attacking barnacles is advantageous over drilling within the context of an optimal foraging theory. Rockey intertidal field and laboratory experiments at Palos Verdes and Los Angeles, California, respectively, in 1981–1982 revealed, that snails with a shell spine have lower handling times and feed at a greater rate than spineless snails which drill their prey. Spine penetration of prey as opposed to drilling takes considerably less time than a tidal cycle. This is expected to increase the success rate for completion of feeding, since during tidal flux snails risk being dislodged. Plasticity in attack mechanisms allows A. spirata with broken spines to penetrate prey by drilling while undergoing spine repair. Differences exist in spine-feeding by A. spirata on B. glandula and C. fissus. The attack process takes more than twice as long when snails attack B. glandula versus C. fissus. However, there is no difference in the mean number of spine thrusts required to penetrate the opercular plates of the two species. When feeding on the larger barnacle B. glandula, A. spirata ingests significantly greater dry weight per unit handling time than with C. fissus.     

Large eddy simulation of flow and scalar transport in a vegetated channel

Predicting flow and mass transport in vegetated regions has a broad range of applications in ecology and engineering practice. This paper presents large eddy simulation (LES) of turbulent flow and scalar transport within a fully developed open-channel with submerged vegetation. To properly represent the scalar transport, an additional diffusivity was introduced within the canopy to account for the contribution of stem wakes, which were not resolved by the LES, to turbulent diffusion. The LES produced good agreement with the velocity and concentration fields measured in a flume experiment. The simulation revealed a secondary flow distributed symmetrically about the channel centerline, which differed significantly from the circulation in a bare channel. The secondary circulation accelerated the vertical spread of the plume both within and above the canopy layer. Quadrant analysis was used to identify the form and shape of canopy-scale turbulent structures within and above the vegetation canopy. Within the canopy, sweep events contributed more to momentum transfer than ejection events, whereas the opposite occurred above the canopy. The coherent structures were similar to those observed in terrestrial canopies, but smaller in scale due to the constraint of the water surface.     

Stable carbon isotope ratios in Red Sea barnacles (Cirripedia) as an indicator of their food source

The stable isotope ratio ¹²C/¹³C was used to investigate the source of carbon in free-living barnacles and in coral-inhabiting barnacles from the Red Sea. The δ¹³C of most of the barnacles collected on the open shore ranges between −17.5 and −19.7‰, indicating relative enrichment of light carbon originating from the open-sea phytoplankton. Those collected in closed habitats showed heavier isotopic composition. The δ¹³C of the coral-inhabiting barnacles ranges from −14.1 to −16.7‰, suggesting that the carbon contribution of open-sea plankton to these barnacles is less important than it is to free-living barnacles. We hypothesize that coral organic matter and zooxanthellae expelled by the host coral contribute carbon to the barnacle, and that a mixture of this relatively heavy carbon with carbon from other sources is responsible for the high values of δ¹³C in coral barnacles. Received: 28 February 1997 / Accepted: 16 September 1997     

Desiccation as a factor in the intertidal zonation of barnacles

Four species of balanomorph barnacles, Balanus crenatus Brugière, B. balanoides (L.), Elminius modestus Darwin and Chthamalus stellatus (Poli), were studied to assess the susceptibility of intertidal barnacle species to desiccation. Known sized samples of barnacles were exposed to controlled desiccating conditions and subsequent survival and water loss were determined. It is clear that the ability to live high on the shore is dependent on a reduction of the overall permeability to water loss. Because of greater surface area to volume ratios, small stages are particularly prone to desiccation. In normal intertidal emersion periods, small stages of B. crenatus particularly, and also of B. balanoides and E. modestus which are similar in their desiccation resistance, would be susceptible to desiccation at normal temperatures and low humidities. Large barnacles would be more prone to death from high temperatures when the tide is out. The spat of C. stellatus, although surviving much longer than spat of larger dimensions of the other species, must also be prone to prolonged emersion conditions at high shore levels.     

The functional morphology and development of the alimentary tract of larval and juvenile barnacles (Cirripedia: Thoracica)

The alimentary tract of the nauplius larva of Balanus spp. consists of cuticle-lined foregut and hindgut, with intervening endodermal midgut constricted into anterior and posterior regions. The anterior midgut cells in the region of the constriction (constriction cells) secrete proteins (probably digestive enzymes). The remaining anterior midgut cells, often containing lipid droplets, form the absorptive region of the tract. Glycoprotein globules and lipid droplets within anterior midgut cells are the remants of the yolk in a pre-hatched larva, this yolk additionally supporting the larva through the non-feeding first nauplius stage. Nauplius Stages II to VI are actively feeding planktonic stages which increase in size and build up lipid reserves. These accumulated reserves support the non-feeding cyprid, first through its planktonic life and then through settlement and subsequent metamorphosis to the juvenile barnacle. Juvenile barnacles start to feed between 2 and 5 days after metamorphosis.     

Effects of disc and arm loss on regeneration byMicrophiopholis gracillima (Echinodermata: Ophiuroidea) in nutrient-free seawater

Clibanarius longitarsus (De Haan), a hermit crab, feeds by means of both micro- and macrofeeding. Microfeeding is of two types: filter feeding and deposit feeding. In macrofeeding, the animal depends mainly on green algae, barnacles and some worms, etc. In filter feeding, the hermit crab uses its paired antennules for trapping microorganisms drawn into the water current created by the second and third maxillipeds; the antennae do not play any role in filter feeding. In deposit feeding, the hermit crab uses its chelae as well as pereiopods for toughing and obtaining detritus food material. In macrofeeding, the organism employs sharp chelae to collect small pieces of muscle from barnacles and then transfer them to the inner mouth parts. In algal feeding, the chelae as well as maxillipeds help in collecting and moving food material towards the mouth. In this investigation functional organisation ofC. longitarsus mouth parts was studied in detail with reference to the various feeding mechanisms, in specimens collected from the intertidal region of Bheemunipatnam, Andra Pradesh, India, in 1988 and 1989.     

水动力条件对湖泊水体磷素质量浓度的影响

以环形水槽为研究手段，利用其可控的流速及可模拟的无限长，解决了前人未解决的湖泊水体水动力难以真实模拟的难题，模拟研究了不同流速对湖泊(太湖)水体中磷素质量浓度的影响。研究表明，随着水体流速的变化，湖泊水体中TP质量浓度的变化呈现3个阶段，即下降期、上升期和突增期。从物理化学和泥沙起动理论两方面，结合水流对悬浮物和沉积物的作用，分析了各阶段产生的原因。文章认为下降期的产生是因为在低流速下，一部分磷被悬浮物的絮凝沉淀带走所引起；上升期的产生则是因为流速上升扰动沉积物，使其达到少量动状态所引起；突增期的产生则是因为流速导致了沉积物普遍动而产生的。在研究范围内，溶解性磷质量浓度与水体流速有着明显的正相关关系；而在低流速下，溶解性磷是TP的主要组成成分，其质量浓度的相对比例可高达87％。结合太湖的有关研究，文章认为这是水华现象产生的关键原因。     

Physiological tolerance predicts species composition at different scales in a barnacle guild

This study examined how the species composition of an intertidal barnacle guild varied according to physical gradients in the environment at small scales governed by microclimates, medium scales of wave exposure and large scales of latitude. Barnacle distributions at small and medium scales were sampled in Ireland between 51°29′ and 52°44′N and 6°50′ and 10°08′W. Sampling on European shores spanned ~18° latitude from 37°05′ to 55°16′N. Barnacle surveys mainly took place in 2003–2004. An index of wave fetch was calculated along the wave exposure gradient using a digital coastline-based model that was supported by a biological exposure scale. A ‘dryness’ index was defined according to mean monthly wind speed, fetch along the average wind direction and mean monthly air or sea surface temperatures for 2 years (January 2001–December 2002) which is the period when the most recent adults in the barnacle community would have settled and grown to adulthood. The proportion of the dry-loving barnacle Chthamalus montagui Southward increased within the barnacle guild at all scales as the habitat became warmer and drier. Barnacle densities were high in all habitats, mean densities ranged from a minimum of 4.16 cm⁻² on moderately exposed shores to a maximum of 6.27 cm⁻² in sunlit or south-facing microclimates. Percentage cover of barnacles across the gradient of latitudes was usually >70%. The results suggest that the distribution and abundance of interacting barnacle species on European coasts is strongly controlled by abiotic factors, most likely temperature and desiccation.