X-ray diffraction study of calcification processes in embryos and larvae of the brooding oyster Ostrea edulis

X-ray powder diffraction was used to study shell calcifications of the oyster Ostrea edulis, sampled in the Limski Kanal, Istria (Adriatic Sea), in May 1992. All the developmental stages were followed, from the embryonic stage through the transition between the trochophore and veliger larva (prodissoconch I and II) and later, after swarming, the pelagic free-swimming larval stages, up to their settlement and attachment (from the D-shaped to the fully formed pediveliger larva), and finally during metamorphosis and juvenile stages (dissoconch). In the first gastrula stage, only an amorphous tissue is present (a periostracum and organic matrix). The beginning of shell formation (at the end of gastrulation) in early trochophores is manifested by the appearance of calcite (up to 1–7% of total volume) and then aragonite (about 1%). In the later stage of the veliger larva the fraction of calcite decreases as well as the amorphous fraction, while the fraction of aragonite rapidly increases. In the prodissoconch II stage and during the whole pelagic period aragonite is dominant, accompanied by a very small amorphous fraction and traces of calcite. The shell mineral composition does not change until metamorphosis, whereupon the fraction of calcite rapidly increases and the fraction of aragonite decreases. The postmetamorphic valves of the juvenile and adult oyster consist mainly of calcite, except the resilium and myostracum which remain aragonitic, possibly as a continuation of the inner layer of the larval shell. Received: 28 May 1997 / Accepted: 1 July 1997     

X-ray diffraction study of the first larval shell of Ostrea edulis

X-ray powder diffraction was used to study the calcification of the first larval shell of Ostrea edulis (sampled in Limski kanal, Istria, Adriatic Sea in April 1986) from the trochophore stage to the veliger larvae (prodissoconch I), and development of the latter up to several days postfertilization (prodissoconch II). In the first stage, only the amorphous component is present (periostracum and organic matrix). The beginning of shell formation is manifested by the appearance of calcite (up to 1–4% of the total vol.) and then aragonite (2 to 7%). In a later stage of the veliger larvae the fraction of calcite decreases, as well as the fraction of the amorphous component, while the fraction of aragonite rapidly increases. In the prodissoconch II stage, aragonite is dominant, with a very small amount of amorphous component and traces of calcite. In contrast, the valves of the adult O. edulis are composed mainly of calcite, with traces of aragonite.     

The uptake and distribution of 65Zn in oysters

Over a period of 6 weeks in aquaria, Portuguese oysters Crassostrea angulata, accumulate ⁶⁵Zn to a greater extent than do native Ostrea edulis, although intake rates for any particular organ in either species are quite similar. The general distribution pattern of radioactivity in the tissues is similar to that observed for stable zine and ⁶⁵Zn in other oyster species, concentration occurring to the greatest extent in gills and mantle, and least in muscle. The observed equilibrium concentrations and biological half-lives are considerably less than those measured in the natural environment, and the significance of this and its bearing on the mechanism of uptake is discussed. Cobalt and iron depress the rate of ⁶⁵Zn uptake by both oyster soft tissues and the shell. The limiting effect in soft tissues is probably due to competition for sites at the actual point of uptake. The distribution of ⁶⁵Zn in tissue subcellular fractions separated by centrifugation shows the greatest concentration of the radioisotope in the insoluble tissue components of gills, mantle and heart. Appreciable amounts of ⁶⁵Zn are associated with tissue proteins.     

Environmental and structural control of trace elements in barnacle shells

The shell composition of 5 species of barnacles [Balanus balanoides (L.), B. crenatus Bruguière, B. hameri Ascanius, Elminius modestus Darwin and Chthamalus stellatus (Poli)] collected from four different sites on the coast of North Wales and one site in the Irish Sea were studied using chemical, X-ray diffraction and electron-microprobe analyses. All the shells consisted of calcite. The trace substances studied were Mg, Sr, Na, Mn, PO₄, and SO₄. Other trace elements detected included Si, Li, Ba, Zn, Cl, and Al. For each species, Mn was the only element in the shell which varied significantly from one locality to another. Variation of concentration of Mn in the shells may be related to the variations of the concentration of Mn in the water, since concentrations in the shells were highest in (estuarine) waters containing high concentrations of Mn. In Balanus balanoides L. and Elminius modestus Darwin, the Mn:Ca and Mg:Ca ratios decreased with decreasing shore level and Sr:Ca varied in the opposite direction. When B. crenatus Bruguière, a subtidal and lower littoral species, and B. hameri Ascanius, a Continental-Shelf species, were compared with the intertidal, species B. balanoides and E. modestus, the Mn:Ca and Mg:Ca ratios followed the same decreasing trend, and the Sr:Ca ratios the same increasing trend with increasing depth. These variations may be related either to increased growth rate of the shells of each species or maxium temperature to which the species is exposed, or both. The differences between species are more consistently reflected, in the concentration of Mn. However, since the concentration, of Mn is correlated with the amount of organic matter in the shell, the specific variations may reflect only the variations in the amount of organic material in the shell of each species.     

Morphological and habitat divergence in the intertidal limpet Patelloida pygmaea

In the intertidal limpet Patelloida pygmaea, two distinctive morphs, the forms pygmaea and conulus, have been recorded. The former possesses a flat elongated shell, and the latter has an extremely high round shell. It has been observed in the field that pygmaea is found on oyster shells Crassostrea gigas. The form conulus uses an unusual substrate for attachment. It is found on the living shells of the intertidal gastropod Batillaria cumingi. Although conulus is normally found only on shells of Batillaria, it can also be found on oyster shells when pygmaea and Batillaria shells are not present in nature. An electrophoretic analysis of allozymes showed that these two forms are reproductively isolated from each other and coexist without gene exchange on the same mudflat. Laboratory experiments showed that pygmaea prefers oyster shells and conulus prefers Batillaria shells as substrates for attachment when both oyster and Batillaria shells are present. The form pygmaea did not attach to Batillaria shells, even when only Batillaria shells were available. However, conulus also attached to oyster shells when Batillaria shells were not available. The proportion of individuals of conulus that attached to oyster shells decreased significantly when pygmaea was attaching to the oyster shells. These results suggest that pygmaea is ecologically more specialized to living on oyster shells than conulus.     

Effects of calcium,strontium, and magnesium on the coccolithophorid Cricosphaera (Hymenomonas) carterae. I. Calcification

The present investigation concerns the effects of calcium, strontium, and magnesium on calcification and mineralogy of the calcified bodies (coccoliths) of the coccolithophorid Cricosphaera (Hymenomonas) carterae. The capacity of cells to calcify in various concentrations of these ions was examined following preliminary decalcification in CO₂. At a concentration of 10^-2 M Ca, 75% of the cells formed coccoliths within 24 h and almost all cells were recalcified after 2 days. At 10^-3 or 10^-4 M Ca no recalcification occurred. However, with the addition of Sr to the Ca-deficient media, calcification took place as shown by observations of coccoliths and by analysis of Ca. The percentage of calcified cells increased with increasing concentrations of Sr. Strontium added to a Ca-deficient media was much more effective than an equivalent concentration of Ca. No Sr was deposited in the coccoliths. X-ray analysis demonstrated that calcite was deposited by cells in all concentrations of Ca and Sr at which calcification took place. At concentrations of Mg in the media from O. O to 4.2×10^-2 M, the cells retained their ability to calcify, although calcification was markedly reduced in the absence of Mg. In low Mg concentrations (1.3×10^-4 and 4.2×10^-6 M), the coccoliths were 60% calcite and 40% aragonite, and in teh absence of Mg, only calcite was formed.     

Phylogeographic study of the dwarf oyster, Ostreola stentina, from Morocco, Portugal and Tunisia: evidence of a geographic disjunction with the closely related taxa, Ostrea aupouria and Ostreola equestris

Despite the economic importance of oysters due to the high aquaculture production of several species, the current knowledge of oyster phylogeny and systematics is still fragmentary. In Europe, Ostrea edulis, the European flat oyster, and Ostreola stentina, the Provence oyster or dwarf oyster, are both present along the European and African, Atlantic and Mediterranean, coasts. In order to document the relationship not only between O. stentina and O. edulis, but also with the other Ostrea and Ostreola species, we performed a sequence analysis of the 16S mitochondrial fragment (16S rDNA: the large subunit rRNA-coding gene) and the COI fragment (COI: cytochrome oxidase subunit I). Oysters were sampled from populations in Portugal (two populations), Tunisia (two populations) and Morocco (one population), identified as O. stentina on the basis of shell morphological characters. Our data supported a high degree of differentiation between O. stentina and O. edulis and a close relationship between O. stentina and both Ostrea aupouria (from New Zealand) and Ostreola equestris (from Mexico Gulf/Atlantic). The status of this geographic disjunction between these closely related species is discussed. Furthermore, although identified in a separate genus Ostreola by Harry (Veliger 28:121–158, 1985), our molecular data on O. stentina, together with those available for the other two putative congeneric species, O. equestris and Ostreola conchaphila, would favour incorporation of Ostreola in Ostrea. Finally, a PCR-RFLP approach allowed the rapid identification of O. edulis and O. stentina.     

Epibiosis on cerith shells in a seagrass bed: correlation of shell occupant with epizoite distribution and abundance

The cerith Cerithium atratum (Born 1778) is an abundant gastropod in the seagrass beds at Cabo Frio, Brazil. In order to estimate the ecological importance of cerith shells as a rare hard substratum in the seagrass bed, the abundances of C. atratum and of cerith shells occupied by hermit crabs were quantified. The mean densities of C. atratum and hermit crabs were 1887 and 100 individuals m⁻², respectively, and these provided 0.5 m² shell area m⁻² available for epizoite colonization. The tube-forming polychaete Hydroides plateni (Kinberg 1867) and oyster Ostrea puelchana Orbigny, 1841 were the dominant visible epizoites on inhabited cerith shells. These epizoite populations were compared in order to investigate whether the temporal and spatial patterns in the epibiotic community were related to ecological and behavioral aspects of the occupant species (cerith or hermit crab). Larger cerith shells had a greater abundance of epizoites. Each epizoite showed a preference for a different occupant of the shells (the oyster for C. atratum and the polychaete for cerith shells occupied by hermit crabs). The oyster showed a seasonal pattern in abundance on C. atratum, being more common in fall (March–April). The distribution of the epizoites on the shells depended on the shell occupant species and was probably related to their different foraging activity –C. atratum ploughs half buried through the sediment, while the hermit crab crawls on the sediment surface. In both cases, the activity of the shell occupant was considered to be beneficial to the epizoites, as empty shells and shell fragments did not support a macroepifauna. Received: 1 May 2000 / Accepted: 8 August 2000     

Shell ecophenotype in the blue mussel (<Emphasis Type="Italic">Mytilus edulis</Emphasis>) determines the spatial pattern in foraging behaviour of an oystercatcher (<Emphasis Type="Italic">Haematopus ostralegus</Emphasis>) population

When feeding on blue mussels (Mytilus edulis), oystercatchers (Haematopus ostralegus) either stab into the mollusc’s gaping valves or hammer through its dorsal or ventral shell. Whilst the selectivity of hammering and stabbing oystercatchers for specific prey morphologies has been well studied, the way in which the effects of environment on M. edulis morphology can in turn affect feeding methods of H. ostralegus is very poorly understood. Based on morphological analyses on randomly selected shells from three intertidal zones, this study failed to detect differences in morphology or distribution of dorsally and ventrally hammered shells but confirms the finding of previous authors that hammering oystercatchers select thinner mussels than stabbing birds. Additionally, we show that this difference in optimal prey morphology can lead to spatial patterns in oystercatcher feeding behaviour. Whilst at the low intertidal and higher mid intertidal zones, characterised by comparatively thick shells, most empty shells had apparently been stabbed, hammering was the dominant feeding behaviour at the lower mid intertidal zone, where shells were thinner. Preference of hammering birds for smaller mussels was not ubiquitous. Sagittal shell shape was predominantly influenced by allometric growth effects and had only minor effect on prey selection. All oystercatchers preferred less inflated mussels, with the degree of shell inflation gradually increasing with higher intertidal elevation. Our results illustrate the importance of small-scale patterns in prey ecophenotypes in determining the distribution and feeding dynamics of wading birds.     

An exploratory study with the proton microprobe of the ontogenetic distribution of 16 elements in the shell of living oysters (Crassostrea virginica)

Study of the chemical composition of shell of exoskeletonous organisms in the past has required the sacrifice of the organism. Because the beam of the proton microprobe is relatively nondestructive and analyzes the surface layer of the shell, organisms do not have to be killed. The present paper presents results of a preliminary experiment in which distribution of elements (Na to Sr) in shell of living juvenile oysters, Crassostrea virginica (Gmelin), was studied in situ with a proton microprobe at monthly intervals for four months. The relative concentration of 16 elements was measured in the newly deposited prismatic edge of the right valve of three oysters reared in controlled laboratory conditions. Na, Mg, Al, Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Cu, Zn, Br, and Sr were detected in concentrations as low as a few parts per million relative to the concentration of standards added to pure CaCO₃. Concentration of elements varied nominally among shells of the three individual oysters and in their successive ontogenetic stages. Fluctuations in concentration of Na, Mg, S, Cl, Ca, Mn, Fe, Cu, and Zn were generally similar in the two normally growing oysters, but differed from those in the oyster that stopped growing. Trends in concentration of Al, Si, and Sr were similar in the three oysters: those of Br were variable. Relative concentrations of Na, Cl, S, Mn, Fe, and Zn increased slightly with age of oysters, that of the other elements stayed relatively constant. Concentration of most elements was higher in shell than in seawater. Variable concentrations, especially of Na, Cl, and Si in valve edges, tend to support the hypothesis of earlier workers that separate mineral phases are present as impurities entrapped within the shell during calcification.     

Effect of salinity fluctuation on the osmotic pressure and Na+, Ca2+ and Mg2+ ion concentrations in the hemolymph of bivalve molluscs

Specimens of Chlamys opercularis, Modiolus modiolus, Mytilus edulis, Crassostrea gigas, Scrobicularia plana and Mya arenaria were exposed to both gradual (sinusoidal) and abrupt (square-wave) salinity fluctuations and measurements made of osmotic, Na⁺, Mg²⁺ and Ca²⁺ concentrations in the hemolymph and where applicable in the mantle fluid. In both sinusoidal and square-wave regimes fluctuating between 100 and 50% seawater (100%=ca. 32 S), the hemolymph Na⁺, Mg²⁺, Ca²⁺ and osmotic concentrations followed the concentrations of the external medium in Chlamys opercularis. The hemolymph and mantle fluid osmotic Na⁺, Mg²⁺ and Ca²⁺ concentrations of Modiolus modiolus, Mytilus edulis, Crassostrea gigas and S. plana followed those of the external medium as long as the molluscs' shell valves remained open. There were no changes in the ionic or osmotic concentrations of the hemolymph or mantle fluid of any of these species during periods of shell-valve closure. The hemolymph osmotic, Na⁺ and Mg²⁺ concentrations of wedged-open Modiolus modiolus, Mytilus edulis, C. gigas and S. plana followed those of the external medium. Hemolymph Ca²⁺ concentrations showed a damped response in C. gigas and Mytilus edulis. The hemolymph osmotic, Na⁺, Ca²⁺ and Mg²⁺ concentrations of Mya arenaria fluctuated in a similar manner to the external medium, but were damped. Wedged-open Mytilus edulis exposed to fluctuating salinity and supplied with a constant supply of 10 mM Ca²⁺ showed greater changes in hemolymph ionic and osmotic concentrations than M. edulis exposed to the same salinity fluctuation without a constant Ca²⁺ supply. Chlamys opercularis and Modiolus modiolus survived in a 50% seawater minimum sinusoidal salinity fluctuation for 10 days; wedged-open M. modiolus survived only 3 days. Burrowing had no effect on the osmotic, Na⁺, Mg²⁺ or Ca²⁺ concentrations of the hemolymph of Mya arenaria or S. plana exposed to fluctuating salinities. All of the species studied were shown to be osmoconformers.     

Variation in strength of attachment to the substrate explains differential mortality in hybrid mussel (Mytilus galloprovincialis and M. edulis) populations

Mussel samples were collected from a hybrid mussel (Mytilus galloprovincialis and M. edulis) Population at Croyde, southwest England, in January, March and May 1990. The strength of attachment of each mussel to the substrate was measured with a spring balance. A number of diagnostic characters were also recorded. These are shell lengh, width and height, mantle colour and genotype at two allozyme loci, esterase-D and octopine dehydrogenase. Multiple-regression analysis was used to assess the effect of the diagnostic characters on strength of attachment as dependent variable. Mussels possessing the relatively high shells and darker mantle colouration characteristic of M. galloprovincialis had higher values, on average, for strength of attachment than mussels resembling M. edulis. Phenotypically intermediate mussels had intermediate values for strength of attachment. The results suggest an adaptive difference which can account for reports of differential mortality acting in favour of M. galloprovincialiis.     

Effects of seawater pCO2 and temperature on shell growth, shell stability, condition and cellular stress of Western Baltic Sea Mytilus edulis (L.) and Arctica islandica (L.)

Acidification of the World’s oceans may directly impact reproduction, performance and shell formation of marine calcifying organisms. In addition, since shell production is costly and stress in general draws on an organism’s energy budget, shell growth and stability of bivalves should indirectly be affected by environmental stress. The aim of this study was to investigate whether a combination of warming and acidification leads to increased physiological stress (lipofuscin accumulation and mortality) and affects the performance [shell growth, shell breaking force, condition index (C_i)] of young Mytilus edulis and Arctica islandica from the Baltic Sea. We cultured the bivalves in a fully-crossed 2-factorial experimental setup (seawater (sw) pCO₂ levels “low”, “medium” and “high” for both species, temperature levels 7.5, 10, 16, 20 and 25 °C for M. edulis and 7.5, 10 and 16 °C for A. islandica) for 13 weeks in summer. Mytilus edulis and A. islandica appeared to tolerate wide ranges of sw temperature and pCO₂. Lipofuscin accumulation of M. edulis increased with temperature while the C_i decreased, but shell growth of the mussels only sharply decreased while its mortality increased between 20 and 25 °C. In A. islandica, lipofuscin accumulation increased with temperature, whereas the C_i, shell growth and shell breaking force decreased. The pCO₂ treatment had only marginal effects on the measured parameters of both bivalve species. Shell growth of both bivalve species was not impaired by under-saturation of the sea water with respect to aragonite and calcite. Furthermore, independently of water temperatures shell breaking force of both species and shell growth of A. islandica remained unaffected by the applied elevated sw pCO₂ for several months. Only at the highest temperature (25 °C), growth arrest of M. edulis was recorded at the high sw pCO₂ treatment and the C_i of M. edulis was slightly higher at the medium sw pCO₂ treatment than at the low and high sw pCO₂ treatments. The only effect of elevated sw pCO₂ on A. islandica was an increase in lipofuscin accumulation at the high sw pCO₂ treatment compared to the medium sw pCO₂ treatment. Our results show that, despite this robustness, growth of both M. edulis and A. islandica can be reduced if sw temperatures remain high for several weeks in summer. As large body size constitutes an escape from crab and sea star predation, this can make bivalves presumably more vulnerable to predation—with possible negative consequences on population growth. In M. edulis, but not in A. islandica, this effect is amplified by elevated sw pCO₂. We follow that combined effects of elevated sw pCO₂ and ocean warming might cause shifts in future Western Baltic Sea community structures and ecosystem services; however, only if predators or other interacting species do not suffer as strong from these stressors.     

Shell-size selection by intertidal sympatric hermit crabs

This study evaluated selection for shell size by three species of tropical intertidal hermit crabs, Clibanarius antillensis, C. sclopetarius, and C. vittatus, from species of shells which are frequently used in nature. Crab size and weight were strongly and significantly related to all measured parameters of the selected shells. The strength of these relationships (r² values) depended neither on the crab nor on the shell variables taken into account. The relationships between crab size and the dimensions of the selected shells showed higher r² values than the corresponding relationships with the shells that the crabs had occupied when they were collected (0.482–0.903 in comparison to 0.091–0.652, respectively), indicating that the crabs were occupying sub-optimal shells in nature. Negative allometry was frequently found in the relationships between crab and shell variables, indicating that large crabs select and use proportionally lighter shells than do small crabs. This negative allometry was stronger for the shells used in nature (except for C. antillensis), i.e. larger crabs tended to select heavier shells in the laboratory than in nature. Different allometric relationships were also recorded among the dimensions of shells used in nature and those selected by the hermit crabs in free-access experiments: as shell length increased, the selected shells were heavier and had larger apertures than the shells used in nature. The relationships between crab size and the length and weight of the selected shells did not depend on the species of crab or species of shell, but only on crab size. Therefore, analyses using these variables can be performed without taking the species of crab or shell into account, i.e. data from different crab or shell species can be pooled. The influence of crab and/or shell species was recorded only in the models fitted for aperture length and width, variables which were more related to shell architecture than did shell length or weight. In contrast, if crab weight is used as an independent variable, different crab or shell species can be analyzed together independently of the particular shell parameter. This indicates that crab weight may be less susceptible than crab shield length to shell morphological constraints. Finally, the results indicate that the preferred size of a given shell type chosen by a given hermit crab will depend more on crab size or weight, than on the crab or shell species under consideration, i.e. crab shell-size relationships are not species specific.Communicated by P.W. Sammarco, Chauvin     

Comparative vulnerability to predators,and induced defense responses,of eastern oysters Crassostrea virginica and non-native Crassostrea ariakensis oysters in Chesapeake Bay

Management agencies are considering introducing the Suminoe oyster Crassostrea ariakensis into Chesapeake Bay, USA. It is unknown if the growth of feral populations of this non-native oyster would be regulated by the same predators that once controlled the abundance of the native eastern oyster C. virginica. In laboratory studies, we compared the relative susceptibility of juvenile diploids (shell height < 25 mm) of both oyster species to invertebrate predators of eastern oyster juveniles. Predators included four species of mud crabs [Rhithropanopeus harrisii (carapace width 7–11 mm), Eurypanopeus depressus (6–21 mm), Dyspanopeus sayi (8–20 mm), and Panopeus herbstii (9–29 mm)], the blue crab Callinectes sapidus (35–65 mm), and two sizes of polyclad flatworms (Stylochus ellipticus and possibly Euplana gracilis; planar area ≲5 mm² and ∼14 to 88 mm²). All four species of mud crab and the blue crab preyed significantly (ANOVA, P ≤ 0.05) more on C. ariakensis than on C. virginica, but predation by flatworms of both sizes did not differ significantly between oyster species. The greater susceptibility of C. ariakensis to crab predation was likely due to its shell compression strength being 64% lower than that of C. virginica (P = 0.005). To test for predator-induced enhancement of shell strength, we held oysters of both species for 54 days in the presence of, but protected from, C. sapidus and R. harrisii. Crabs were fed congeneric oysters twice weekly within each aquarium. Compared to controls, shell strength of C. virginica exposed to R. harrisii increased significantly (P < 0.043), as did shell strength of both oyster species exposed to C. sapidus (P < 0.01). Despite the changes in shell strength by both oyster species in the presence of C. sapidus, the shell of C. ariakensis remained 57% weaker than C. virginica. We conclude that, because C. ariakensis exposed to predators continued to have a weaker shell relative to C. virginica, the natural suite of crab and flatworm predators in Chesapeake Bay will likely serve to control the abundance of feral C. ariakensis. We caution that the situation in the natural environment may be sufficiently different in some locations that C. ariakensis may be able to compensate for its greater vulnerability to crab predation and hence become a nuisance species.     

Temperate reefs in a changing ocean: skeletal carbonate mineralogy of serpulids

We present a review of the published data about serpulid skeletal carbonate geochemistry, augmented with new data from the Southern Hemisphere. We know something about skeletal carbonate mineralogy of 15 % of extant species (n = 52); and about half of extant genera (n = 25). Serpulid worm tubes vary in their skeletal mineralogy from entirely aragonitic (about 24 % of species) to entirely high-Mg calcite (40 %) to mixtures of the two. Mg in calcite ranges from 7 to 15 wt% MgCO₃, with a mean of 11 wt% MgCO₃. Little mineralogical variation within individuals or species can be found in aragonitic specimens, whereas high-Mg calcitic species show somewhat more variability in both calcite and Mg content, and those with mixed mineralogies are highly variable. These three groups correspond broadly with currently accepted clades. Given this strong phylogenetic signal, we analysed the data using phylogenetically independent contrasts, a statistical approach that separates genotypic from phenotypic variability; we found that variations which might be ascribed to environment were generally weak. The mineralogy of serpulid tubes makes them particularly vulnerable to ocean chemistry changes. While some serpulids appear to be able to adjust their tube mineralogy in order to adapt to sea-water chemistry, overall strength and elasticity may be sacrificed when they do. The biodiverse reef habitat provided by serpulids in some temperate regions may be the only complex solid habitat available, and loss or compromise of these temperate reefs will most likely have deleterious flow-on effects on temperate benthic communities.     

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.     

X-ray diffraction study of mineral components in calcareous algae (Corallinaceae,Rhodophyta)

The mineral composition of nine species of red calcareous algae (Corallinaceae, Rhodophyta) collected in the Adriatic Sea in 1987 and 1988 was examined by X-ray powder diffraction (counter diffractometer, monochromatized CuK radiation). In addition, a comparison between the calcareous algae from the north Adriatic (Rovinj area) and the central Adriatic (Kornati Islands) with regard to genus, species and environmental factors was undertaken. All analyzed samples contained magnesium calcite, which was dominant in all but in two cases, where aragonite was the main phase. Diffraction lines of magnesium calcite were broadened and shifted toward higher Bragg angles in relation to pure calcite. Supposing that in the calcite crystal lattice only magnesium replaces calcium, it follows that the fraction of magnesium in magnesium calcite, found from diffraction line shifts, would be 18 molar % (M%). Aragonite was dominant (75 to 80 M%) in two samples of Pseudolithophyllum expansum collected at Kornati Islands in 1987 and 1988. These two samples also contained magnesium calcite and a small fraction of calcite (5 to 10 M%). In other studied samples aragonite was detected in small fractions, up to 10 M%. The elemental analysis of corallinacean algae obtained by X-ray spectroscopy showed that the fraction of the metals Sr, Fe, Mn, Zn, Pb, Br, Cu and Rb was very small (15 to 2000 ppm). In most samples other expected minerals were detected in small fractions, such as sylvite (KCl, up to 2 M%), quartz (-SiO₂, up to 2 M%) and magnesite (MgCO₃, only in one sample, 1 M%). The results show that calcareous algae are able to deposit a mixture of magnesium calcite, calcite and aragonite. Such a large molar fraction of aragonite in the alga P. expansum, or in any other corallinacean algae, has not been noted in recent literature. It seems that a complexity of microclimatic and oceanographic factors may influence the diversity of two localities and cause some exchange in living organisms. In addition, the fact that under certain conditions the same organism is capable of forming different minerals from the same tissue (McConnaughey 1989) confirms our opinion that environmental effects are imprinted in the skeletal composition of calcareous algae P. expansum.     

In situ mapping of growth lines in the calcitic prismatic layers of mollusc shells using X-ray absorption near-edge structure (XANES) spectroscopy at the sulphur K-edge

The microstructure and composition, including chemical speciation of sulphur (S), of two mollusc shells were investigated using a combination of scanning electron microscopy, X-ray absorption near-edge structure spectroscopy (XANES) and electron probe microanalysis (EPMA). The shell of Pinna is composed of monocrystalline, and Pinctada, of polycrystalline, calcite prisms separated by organic-rich walls. Sulphur speciation information from XANES spectra using a scanning X-ray microscope showed that the protein S content of the interprismatic walls is higher than the SO₄ content, whereas the reverse is true for the intraprismatic structures. High-spatial-resolution XANES maps for the different S species across adjacent calcite prisms confirm their distinctive distributions in the molluscan shells and illustrate the presence of narrow, submicron transverse growth features. On a larger scale, a series of wider growth zones, incorporating the submicron zones, are aligned parallel to each other and cross-cut many calcite prisms. EPMA element maps for magnesium (Mg) and S demonstrate that these growth increments are compositionally zoned, comprising alternating layers of high mineral (Mg-rich) and high organic (S-rich) components. Additionally, these maps confirm that the organic interprismatic walls have lower Mg and higher S than the intraprismatic structures.     

Inducible defenses in the eastern oyster Crassostrea virginica Gmelin in response to the presence of the predatory oyster drill Urosalpinx cinerea Say in Long Island Sound

The response of the eastern oyster C. virginica to the presence of the oyster drill Urosalpinx cinerea was examined from July to September 2011. Several aspects of oyster growth were measured, including wet weight, shell weight, and dorsal shell area for oysters collected near Groton, Connecticut (41.32036 N, −72.06330 W). Wet weight and shell weight growth were significantly higher in the presence of the predator U. cinerea, while tissue weight showed no difference from the control. The control group showed more shell area growth and a much lower ratio of shell weight growth to shell area growth. Differences in shell weight to area ratio indicated that C. virginica dramatically shifted from lateral shell growth to shell thickening in the presence of U. cinerea. This inducible defense has not been previously shown for C. virginica and could play an important role in the predator–prey interaction between these two species.