Barnacle Shells Research Articles

Cuckoldry rates in the Molly Miller (scartella cristata; blenniidae), a hole-nesting marine fish with alternative reproductive tactics

Microsatellite markers were developed and employed to assess genetic maternity and paternity of embryos in nest-tended clutches of the Molly Miller (Scartella cristata), a marine fish in which alternative reproductive tactics (ARTs) by males were recently described from behavioral and morphological evidence. Genetic data gathered for 1,536 surveyed progeny, from 23 barnacle-nest holes in a single Floridian population, indicate that on average about 5.5 females (range 3–9) contributed to the pool of progeny within a nest. With regard to paternity, the microsatellite data demonstrate that most of the surveyed nests (82.6%) contained at least some embryos that had not been sired by the nest-tending (bourgeois) male, and overall that 12.4% of offspring in the population had been sired via stolen fertilizations by other males. These are among the highest values of cuckoldry documented to date in nest-tending fishes, and they support and quantify the notion that the nest-parasitic ART is reproductively quite successful in this species despite what would otherwise seem to be highly defensible nesting sites (the restricted interior space of a barnacle shell). Our estimated cuckoldry rates in this population of the Molly Miller are compared to those previously reported for local populations in other nest-tending fish species, with results discussed in the context of ecological and behavioral variables that may influence relative frequencies of nest parasitism.

Darwin and the Barnacle: The Story of One Tiny Creature and History's Most Spectacular Scientific Breakthrough (review)

Reviewed by: Darwin and the Barnacle: The Story of One Tiny Creature and History’s Most Spectacular Scientific Breakthrough Peter C. Grosvenor Darwin and the Barnacle: The Story of One Tiny Creature and History’s Most Spectacular Scientific Breakthrough. By Rebecca Stott. New York: Norton, 2003. Pp. 309. $24.95. The prolific scholarship on Darwinism has diversified and specialized, and there are now detailed studies of Charles Darwin's research on Galapagos finches, his contemplation of the evolutionary development of human emotions, his investigation of pollination in varieties of orchids, and his work on coral reefs. Over the past 15 years or so, these studies of Darwinism have been supplemented very usefully by a substantial body of biographical treatments of Darwin himself. Adrian Desmond's and James Moore's Darwin: The Life of a Tormented Evolutionist (1994) was well received for its location of Darwin's ideas in the context of his life experience. This was followed by Janet E. Browne's monumental two-volume study Darwin: Voyaging (1995) and Darwin: The Power of Place (2002). Randall Keynes—a descendent of both Darwin and of the economist John Maynard Keynes—produced perhaps the most successful human portrait of his subject in Darwin, His Daughter, and Human Evolution (2001). Darwin's personal life also has received fictional treatment, with the publication of Roger MacDonald's Mr. Darwin's Shooter (2000). Rebecca Stott's Darwin and the Barnacle: The Story of One Tiny Creature and History's Most Spectacular Scientific Breakthrough is a welcome addition to the [End Page 624] study of both the idea and the man. Stott heads the Department of English and Drama at Anglia Polytechnic University in Cambridge, and is an Affiliated Research Scholar in the Department of History and Philosophy of Science at Cambridge University. A scholar of Victorian letters, Stott has previous published books on Elizabeth Barrett Browning and Alfred, Lord Tennyson, in addition to numerous articles on Victorian science and society in edited volumes and journals. Her study of Darwin's immersion in barnacle classification between the years of 1846 and 1854 is a daunting undertaking, but the result in a highly readable rendition of a relatively neglected, though demonstrably pivotal, stage in the theorization of natural selection. It was in 1835, when he was the naturalist on board the HMS Beagle, that the 24-year-old Darwin first encountered the barnacle that was to take over his life. Darwin nicknamed the barnacle "Mr. Arthrobalanus" (curiously written as "Mr. Anthrobalanus" on the dust jacket), which later became the official classification of Crytophialus. This particular specimen was then entirely new to biology—an extremely rare barnacle, almost invisible to the naked eye, that did not secrete its own shell. The discovery led Darwin to challenge the existing zoological taxonomy of barnacles, in the process uncovering and illustrating the evolutionary development of adapted species from common ancestry—"The Universe in a Barnacle Shell," as Stott titles her final chapter. The core thesis of the book is stated with admirable concision and clarity in the preface, and supported throughout the rest of the text with narrative flair and an authoritative use of sources. In 1846, Darwin had written an essay containing the essential elements of the natural selection theory and placed the essay in a locked drawer. Stott argues that Darwin's eight-year obsession with barnacles—which seriously eroded his physical and mental health—confirmed the contentions that were to be published in The Origin of Species (1859) but delayed the publication of that text until the findings of the barnacle studies met the emerging standards of scientific verification in the mid-19th century. Stott has abundant justification for concentrating her study of Darwin on his investigation of marine invertebrates. As she convincingly argues, this period in Darwin's life illustrates important features of Darwin's personality, of the intellectual and cultural climate in which he was functioning, and of the state and composition of the scientific community at the time. In terms of Darwin's personality, Stott finds in the barnacle research "an instinct for postponement" (xxiii). As early as 1832, Darwin had expressed to J. S. Henslow his fear of being dismissed as "a Baron...

Spatial point pattern analysis of available and exploited resources

A patchy spatial distribution of resources underpins many models of population regulation and species coexistence, so ecologists require methods to analyse spatially‐explicit data of resource distribution and use. We describe a method for analysing maps of resources and testing hypotheses about species' distributions and selectivity. The method uses point pattern analysis based on the L‐function, the linearised form of Ripley's K‐function. Monte Carlo permutations are used for statistical tests. We estimate the difference between observed and expected values of L(t), an approach with several advantages: 1) The results are easy to interpret ecologically. 2) It obviates the need for edge correction, which has largely precluded the use of L‐functions where plot boundaries are “real”. Including edge corrections may lead to erroneous conclusions if the underlying assumptions are invalid. 3) The null expectation can take many forms, we illustrate two models: complete spatial randomness (to describe the spatial pattern of resources in the landscape) and the underlying pattern of resource patches in the landscape (akin to a neutral landscape approach). The second null is particularly useful to test whether spatial patterns of exploited resource points simply reflect the spatial patterns of all resource points. We tested this method using over 100 simulated point patterns encompassing a range of patterns that might occur in ecological systems, and some very extreme patterns. The approach is generally robust, but Type II decision errors might arise where spatial patterns are weak and when trying to detect a clumped pattern of exploited points against a clumped pattern of all points. An empirical example of an intertidal lichen growing on barnacle shells illustrates how this technique might be used to test hypotheses about dispersal mechanisms. This approach can increase the value of survey data, by permitting quantification of natural resource patch distribution in the landscape as well as patterns of resource use by species.

Pumice layers in marine terraces: implications for tectonic uplift rates on the east and northeast coasts of Taiwan over the last hundreds of years

Two very rare pumice-rich layers were recently found at two sites in Taiwan, more precisely in the lowermost marine terrace of the Sanhsientai area on the southeast coast, and in that of the Yenliao area, on the northeast coast. The pumice-rich layer in the former is about 15 cm in thickness and is composed of 60–70% gray to dark gray, subangular to angular pumice fragments with barnacle shell fragments. The layer in the latter, on the other hand, is about 10 cm in thickness and is composed of 40–50% light gray to gray, subrounded to subangular pumice fragments with a few carbonized wood fragments. Despite their different occurrences, both pumice fragments very closely resemble each other in terms of major and trace as well as isotopic compositions and, therefore, may be considered to have come from the same source, the Luzon or Philippine arcs. 14C-dating gives the layers an equal age ranging from around 420 to 402 cal. yr BP. Based on the age and altitude of the marine terraces in the Sanhsientai and Yenliao areas, however, the uplift rates are 10.9 and 5.4 mm/yr, respectively. The results strongly indicate that, firstly, the uplift rates may have accelerated in the last thousands of years during the Holocene in the Sanhsientai–Chengkung area and that, secondly, the northern coastal area of Taiwan likely suffered from a spasmodic uplift in the very latest Holocene.

Extracellular Matrix Molecules Involved in Barnacle Shell Mineralization

AbstractAustromegabalanus psittacusis a large (normally up to 30 cm high) sessile balanomorph barnacle from the coast of Chile and South Peru. Its hard shell is composed of twelve calcareous side plates, six parietes and six radii, joined in the form of a truncated cone opened at the top. Plates rest on a basal disk firmly cemented to the substratum. Although the crystalline microstructure of barnacle's shell has been studied to some extent, its organic composition and the mechanisms governing the biomineralization of such highly ordered nanocomposite have remained obscure. By using X-ray diffraction, infrared spectrometry, SEM and TEM electron microscopy, histochemistry, immuno-histochemistry and -ultrastructure, biochemistry and a crystallization assay, we have studied the cell-shell interactions, the crystalline microstructure of the inorganic moiety and the localization of particular macromolecules, and tested their influence on crystallization.The mineral of the plates and basal disk was calcite showing a (104) preferential orientation. Plates were not solid but porous. While parietes have longitudinal canals (from the base to the apex), radii have transversal canals arranged parallel to the base. These canals are not in the center of the plates but displaced to the outside of the shell delimiting a thinner solid outer lamina and a thicker inner one. The inner lamina consisted of parallel calcified layers separated by organic sheets. These sheets showed autofluorescence and consisted of chitin surrounded by proteoglycans and other minor proteins, which seems to be responsible for the fluorescent behaviour. These organic sheets were also organized as several concentric rings around the canals. The shell matrix obtained after decalcification, which surrounded the crystals, also contained a loose net of such proteoglycans. Mantle epithelial cells covered the entire surface of the inner side of the inner lamina and extend to the plate canals. While isolated chitin did not promote or alter calcite crystallization, the proteoglycan-rich fraction dramatically modified crystal morphology and size. As we have demonstrated in another model of biomineralization, such as the eggshell, hereby we suggest that these structured polyanionic proteoglycan moieties could also be part of the regulatory mechanisms of the barnacle shell mineralization.

The benthic invertebrates of the Salton Sea: distribution and seasonal dynamics

The Salton Sea, California’s largest inland water body, is an athalassic saline lake with an invertebrate fauna dominated by marine species. The distribution and seasonal dynamics of the benthic macroinvertebrate populations of the Salton Sea were investigated during 1999 in the first survey of the benthos since 1956. Invertebrates were sampled from sediments at depths of 2–12 m, shallow water rocky substrates, and littoral barnacle shell substrates. The macroinvertebrates of the Salton Sea consist of a few invasive, euryhaline species, several of which thrive on different substrates. The principal infaunal organisms are the polychaetes Neanthes succinea Frey and Leuckart and Streblospio benedicti Webster, and the oligochaetes Thalassodrilides gurwitschi Cook, T belli Hr.tbe, and an enchytraeid. All but Neanthes are new records for the Sea. Benthic crustacean species are the am phipods Gammarus mucronatus Say, Corophium louisianum Shoemaker, and the barnacle Balanus amphitrite Darwin. Neanthes succinea is the dominant infaunal species on the Sea bottom at depths of 2–12 m. Area-weighted est mates of N. succinea standing stock in September and November 1999 were two orders of magnitude lower than biomass estimated in the same months in 1956. During 1999, population density varied spatially and temporally. Abundance declined greatly in offshore sediments at depths >2 m during spring and summer due to decreasing oxygen levels at the sediment surface, eventually resulting in the absence of Neanthes from all offshore sites >2 m between July and November. In contrast, on shoreline rocky substrate, Neanthes persisted year round, and biomass density increased nearly one order of magnitude between January and November. The rocky shoreline had the highest numbers of invertebrates per unit area, exceeding those reported by other published sources for Neanthes, Gammarus mucronatus,Corophium louisianum, and Balanus amphitrite in marine coastal habitats. The rocky shoreline habitat is highly productive, and is an important refuge during periods of seasonal anoxia for Neanthes and for the other invertebrates that also serve as prey for fish and birds.

Paravireia holdichi n. sp., an enigmatic isopod crustacean from the Canary Islands with affinities to species from New Zealand

Abstract Paravireia holdichi n. sp. is reported from the Canary Islands, western Atlantic Ocean. The new species was discovered within empty barnacle shells in areas of intense tourism. It differs from other species of the genus in having a distinctive shield-like shape of the head and prominent lateral keels on anterior pereonites of males. The genus is unique within the Isopoda in lacking any trace of the uropoda. It is remarkable that the two other known species of the genus occur only in New Zealand. Three species are known, the type species Paravireia typica Chilton, 1925, from the supralittoral, and P. pistus Jansen, 1973, from the sublittoral, each from single localities in New Zealand, while Paravireia holdichi n. sp. is known from several supralittoral locations in the Canary Islands. Comparison with known isopod taxa leads to the conclusion that Paravireia does not fit clearly into any known isopod family, although on the basis of overall similarity of the antennule, antenna, mouthparts and pereopods the genus is regarded as incertae sedis with the strongest affinities to the Sphaeromatidae.

Variation in barnacle recruitment over small scales: larval predation by adults and maintenance of community pattern.

Over small spatial scales, variation in the density of settlers of benthic sessile species is the result of interactions among larval behavior, local hydrodynamic conditions, and the physical, chemical and biological characteristics of the benthic habitat. It has been shown repeatedly that adult benthic filter-feeders can consume larvae of their own and other species, but their effects on the distribution and abundance of recruits have rarely been demonstrated under natural conditions in the field, particularly on hard substrata. Here we experimentally quantified the effect of the large intertidal barnacle, Semibalanus cariosus (Pallas), on the density of recruits of three common barnacle species. The experiments were conducted at the peak of the barnacle recruitment season over three successive years, on the west coast of San Juan Island, Washington. A persistent and well documented community pattern in the mid intertidal zone of the study site is a sparse bed of adult S. cariosus with bare rock spaces essentially devoid of small barnacles among the large individuals. Field experiments consisted of small areas from which either all adult S. cariosus were killed leaving the shells attached to the rock, or live adult barnacles were left intact. Our results showed that over small spatial scales of a few to tens of centimeters, the large barnacle S. cariosus can interfere and significantly reduce net settlement and recruitment of conspecific as well as other barnacle species. Between 65 and 100% reduction in settlement could be attributed to larval predation by adults, as implied by barnacle settlement patterns on different treatments and by the presence of nauplius larvae in cirri and stomach contents of S. cariosus. The negative effect on barnacle settlement was consistent between years of relatively low barnacle recruitment, which appears to be the most common situation at the study site, but it disappeared on a year of unusually high recruitment, when settling larvae seem to have swamped the filtration ability of adult S. cariosus. The different barnacle species displayed contrasting settlement patterns on bare rock and on the lateral shells of the large barnacles, which appear to be a result of differences in larval behavior. Comparisons against the relative availability of these substrata in the experimental plots suggested that larvae of different species sample the benthic microhabitat in very different ways.

The design of mineralised hard tissues for their mechanical functions.

Most hard tissues have as their primary purpose to be stiff. Outside the arthropods, mineralisation of a soft organic matrix is the almost universal method of producing high stiffness. However, stiffening brings with it the undesirable mechanical result of brittleness (lack of toughness). The mineralisation of some tissues, such as bone and dentine, can be modified rather easily, in evolutionary terms, to produce the optimum mix of stiffness with bending strength (which, except at the highest mineralisations, go together) on one hand and toughness on the other hand. However, in most other tissues, such as mollusc shell, echinoderm skeleton, brachiopod shell, barnacle shell and enamel, mineralisation is almost all-or-none, and no subtle gradations seem possible. In such cases, other features, such as architecture, must be modified to produce a useful skeleton. Not only the mechanical properties of the skeletal tissue, but its cost, mass and time taken for production will, biologists tend to assume, be balanced by natural selection to produce a satisfactory result. However, such complexity makes it difficult to be sure that we understand the extent to which mineralised skeletal materials are the best possible solution to the problems facing the animals and that we are not just telling 'Just-So' stories. Furthermore, there are some skeletal materials that do not seem to make much sense at the moment, although no doubt all will become clear eventually.

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).

MAKING MOUNTAINS OUT OF BARNACLES: THE DYNAMICS OF ACORN BARNACLE HUMMOCKING

Like plants, sessile invertebrates are often morphologically modified at high densities. At high densities acorn barnacles commonly form hummocks of tall, densely packed individuals. We examined hummock development and its consequences on filter feeding and growth in the northern acorn barnacle, Semibalanus balanoides. Hummocking occurs in response to high recruitment densities and growth rates, which intensify competition for primary substrate space. In the field, hummocks are more common at low than at high tidal heights, paralleling within-site variation in recruitment and growth rates. Hummocks also are most pronounced at high-flow sites with high barnacle recruitment and growth rates. In laboratory flume studies, particle capture rates were higher for individuals near the peak of hummocks than for solitary individuals, and were lower for individuals in the troughs between hummocks than for solitary individuals. Hummocked individuals are elevated above the surface and are thus likely exposed to higher particle fluxes than either individuals between hummocks or solitary individuals. These patterns in particle capture closely match patterns of barnacle shell growth in the field. The shells of hummocked individuals were larger than those of solitary individuals, which were larger than the shells of individuals in troughs between hummocks. The tissue growth of solitary individuals, however, is lower than that of crowded individuals, apparently since, without neighbors, solitary barnacles must allocate more resources to structural support than do crowded individuals. Thus, crowding may benefit individual barnacles by reducing their skeletal support costs. Most studies of crowding in sessile, space-limited invertebrates have focused on negative, competitive effects. Our results, along with previous work showing that crowding may benefit northern acorn barnacles by buffering them from heat and desiccation stress and increasing reproductive output, illustrate that crowding also can positively affect sessile organisms. We suggest that interactions among most sessile, space-limited invertebrates are best viewed as a balance between negative and positive effects.

Salinity effects on the growth, mortality and shell strength of Balanus amphitrite from the Salton Sea, California

The Salton Sea, the largest lake in California, has a salinity of around 43 g l-1 that is increasing by about 0.4 g l-1 y-1. A 15 month microcosm experiment was conducted to determined the effects of salinity (30, 39, 48, 57, and 65 g l-1) and tilapia ( Oreochromis mossambicus) on an assemblage of benthic and planktonic Salton Sea algae and invertebrates, including the barnacle Balanus amphitrite. Eleven months after the microcosms were established, acrylic plates containing newly settled B. amphitrite collected at the Salton Sea were placed in the microcosms to determine the effects of salinity on their growth and shell strength. The Brody-Bertalanffy growth model was fitted to the B. amphitrite growth data. Growth was fastest at 48 g l-1 and slowest at 65 g l-1. B. amphitrite grown at 39–48 g l-1 were the largest and required the greatest force to break, but the strength of the barnacle shell material declined steadily as the salinity increased. However, B. amphitrite at the higher salinities were shorter and had thicker walls relative to their diameters, which may have increased their structural stability. The effects of salinity on the mortality of adult B. amphitrite was determined in laboratory aquaria set up at 43, 60, 70, 75, 80, 90, and 100 g l-1. Salinities were achieved in two ways: by salt addition and by evaporation. Calculated 12-day LC50 values were 83 g l-1 when salinities were achieved through salt addition and 89 g l-1 when salinities were achieved through evaporation. Differences in B. amphitrite mortality between the two methods illustrate the importance of producing experimental salinity levels carefully. B. amphitrite is expected to become extinct within the Salton Sea when the salinity reaches 70–80 g l-1 and to show marked declines in abundance at salinities as low as 50 g l-1.

Strontium and manganese uptake in the barnacle shell: Electron probe microanalysis imaging to attain fine temporal resolution of biomineralization activity

Barnacles deposit a thin layer of calcium carbonate at the base of the shell in an incremental fashion. The shells are therefore well suited to provide a temporal record of metal exposure, if metals from the water are incorporated into the shell as growth increments form. Fine temporal resolution of metal exposure would prove useful for studying environmental exposure or biomineralization processes. For this study, barnacles were exposed to artificial sea water (ASW) enriched with either strontium, manganese or lead. Barnacles were exposed to different levels of Sr and Mn for different lengths of time from 2 h to 2 d. The elemental composition of the shells was determined by electron probe X-ray microanalysis (EPXMA) imaging. Strontium and Mn were incorporated into the shells in direct proportion to the metal levels in the ASW. A 2 h pulse of 1 mM Mn-enriched ASW did not result in a detectable band of Mn in the shell; however, a 6-h exposure yielded a clearly visible band of Mn-rich shell. Exposure to 0.24 μM Pb-enriched ASW caused marked reduction in the Ca content of the shell; however, a Pb-rich growth band was not detected in the shell. Barnacles analysed by EPXMA imaging provide a sequential record of metal exposure for Mn and Sr, with a time resolution of approximately 6 h. Enrichment of ASW with either Sr or Mn can be used as a probe to monitor biomineralization events.

Miocene barnacle assemblages from southern Spain and their palaeoenvironmental significance

The Tabernas Basin in southeast Spain is a Neogene intermontane basin which filled with sub-aerial and submarine fan conglomerates grading into turbidite sandstones towards the basin centre. The basin history involved the development of Seravallian-Tortonian subaerial fans which coalesced southwards from the basin margin. Increasing water depth in the Tortonian led to a submarine development of these fans. The coarse fan conglomerates are colonized almost solely by barnacles of the species Megabalanus tintinnabulum, known from Miocene-Recent deposits. The barnacles occur in seven preservational-state assemblages, which provide a record of the colonization of stabilized mass-flow conglomerates and of subsequent reworking episodes. M. tintinnabulum is known from intertidal environments today. In situ clusters developed on the fan conglomerates record the transition of the fans from subaerial to submarine environments. Mass-flow deposits rich in barnacle shell debris are representative of basin-wards reworking of intertidal clusters and illustrate relative increase in water depth. A further shallowing episode is identifiable by the recolonization of mass flows by in situ barnacle clusters. This case history is demonstrative of the utility of some barnacles in determining basin history with respect to minor sea level fluctuations.

Barnacle shells as biomonitoring material

During growth of the shell plates of barnacles it is possible that trace and minor metal ions replace calcium in the calcium carbonate lattice. By extension, there may then be a relationship between the concentration of trace metals in the shell and that in the environmental water. Should this relationship exist, then such calcified material may represent a permanent record of environmental trace metal concentrations. Semibalanus balanoides cyprid larvae were collected from the plankton and settled on slates in the laboratory. These slates with their barnacles of known age were placed at several sites around the coast of the Island of Anglesey, Wales. These sites were chosen for their differences in environmental trace metal loading and barnacle growth rates. Subsamples were taken from the populations from each of the sites at 5–6 week intervals over a period of 2 years. Barnacle shell weight and the shell concentrations of magnesium, strontium, manganese, zinc and copper were measured. Barnacles with similar growth rates had higher shell metal concentrations from environments with higher metal loading, while in general smaller shells had higher trace metal concentrations. However, it is concluded that barnacle shell cannot be considered to be an ideal biomonitoring material.

Strontium can be used as a tracer to examine calcification in the adult barnacle (Balanus amphititre amphititre)

Calcification in barnacles occurs at the base of each shell plate; as new CaCO3is deposited at the base, the shell grows upward. Although barnacle shell growth patterns have been characterized, the cellular calcium transport mechanisms involved in biomineralization are unknown; calcium is thought to be transported through the mineralizing epithelial cells into a limited diffusional space between the cells and the shell where calcification occurs. To follow transport of calcium in the cells and newly mineralized shell, one might consider using45Ca and autoradiography.Alternatively, electron probe x-ray microanalysis (EPXMA) imaging has better spatial resolution than autoradiography, but cannot discriminate45Ca from the stable isotope. However, in studies of mammalian bone formation using EPXMA, strontium was used successfully as a tracer for calcium. To assess whether strontium could serve as a tracer for calcium in barnacles, it was first necessary to determine if strontium could be incorporated into barnacle shells.

Indirect Effects and Habitat Use in an Intertidal Community: Interaction Chains and Interaction Modifications

Species may indirectly affect populations of other species in two basic ways. Interac- tion chains result from linked direct interactions between species pairs. Interaction modifica- tions, emergent effects of a multispecies assemblage, result when a third species changes how a pair of other species interacts. Experiments and patterns of abundance in the upper zone of a rocky intertidal community provide examples of both types of indirect effects. By consuming limpets (Lottia digitalis), bird predators indirectly enhance acorn barnacle (Balanus glandula) abundance on horizontal rock benches because limpets dislodge or inadvertently consume young acorn barnacles, an example of an interaction chain. Because L. digitalis has a light-colored shell that is similar in color to barnacle shells, barnacles alter the bird-limpet interaction by changing the ability of birds to find limpets, an example of an interaction modification. Distin- guishing between interaction chains and interaction modifications is important because interac- tion chains can be predicted with only a knowledge of pairwise species interactions while de- scriptions of interaction modifications require a knowledge of all species combinations involved, precluding a priori prediction. By classifying empirically determined indirect effects, the degree to which indirect effects can be predicted from a knowledge of pairwise interactions can be determined, and the mechanisms that cause interaction modifications can be identified to aid in future prediction.

Erratic flint along the Swedish west coast

Abstract Sedimentary rock clasts, especially flint, are abundant in glacial clay and shore deposits in the coastal area of Halland, southwestern Sweden, while they are absent in till and glaciofluvial sediments in this same area. The clasts were deposited as drop from icebergs or drift ice. Qualitative analyses reveal that the most likely provenance of the clasts is the Öresund area, including western Skåne and eastern Danmark. 14C-dating of shells of marine molluses and barnacles enabled a determination of the time interval for the deposition of the sedimentary rock clasts. The deposition started in connection with the deglaciation of the area c. 13,500 B.P., or somewhat later, and it ceased c. 12,200–12,000 B.P. The deposition of sedimentary rock clasts during this period indicates the existence of a glacier with a frontal position in the Kattegat. This glacier is correlated to the Low Baltic readvance.

A complex marine shallow‐water boring trace: Dendrorete balani n. ichnogen. et ichnospec

Tavernier, A., Campbell. S. E. & Golubic, S. 1992 07 15: A complex marine shallow-water boring trace: Dendrorete balani n. ichnogen. et ichnospec. Exceptionally well-preserved reticulate boring patterns in Pliocene barnacle shells are described as a new ichnogenus and species. The organism that formed these borings is a presumed phototroph, possibly belonging to green algae. The principles and needs of a taxonomic treatment of microborings as trace fossils in relation to that of their makers are discussed. It is suggested that ichno-taxonomy be extended to include modern traces, when the taxonomic identity of the agent cannot be ascertained. Bio-erosion, endoliths, ichnofossils, marine, microborings, shallow marine, shells.

Biological and Physical Factors Controlling the Spatial Distribution of the Intertidal AlgaGelidium Pristoidesin the Eastern Cape, South Africa

Gelidium pristoidesdominates the lower and mid-eulittoral zones of rocky shores in the eastern Cape, South Africa. A disproportionately high percentage of the plants is attached to barnacle and limpet shells, or restricted to rock crevices. Our experiments at Port Alfred indicate that this distribution is caused by grazing by the limpetPatella oculusand/or strength of attachment of the plants to the different substrata. Exclusion of limpets caused an approximately four-fold increase in the cover of G.pristoideson rock, and an increase from almost 0 to 80% cover on sterilised (dead) limpet shells. Measurements showedG. pristoidesto be more than 50% more strongly attached to barnacle and limpet shells than to rock. The distribution ofG. pristoideson the various substrata is largely determined by limpet grazing and possibly the different strengths of attachment to the different substrata. The upper distribution limit ofG. pristoidesis set by physical effects of emersion and was largely unaffected by limpet exclusion. Competition with other algae is important in setting the lower limit: in the sublittoral fringe, although limpet exclusion enhanced recruitment, juveniles were later displaced by articulated corallines, and adult transplants senesced because of encrusting coralline epiphytes.