Aragonitic Shells Research Articles

Electron Spin Resonance and Thermoluminescence dating of shells and sediments from Sambaqui (shell mound) Santa Marta II, Brazil

In Tupi, the word Sambaqui means “mound of shells”. These archaeological sites are cultural vestiges left by the prehistoric occupation of the Brazilian coast from five to six thousand years ago. Mollusks, fishes, and other marine edible foods were important for the survival of this population. The remains of foods, mainly shells, were heaped up, giving a mound of different proportions, which became part of the landscape of the Brazilian coastal plain. Due to the large number of Sambaquis in Brazil and considering that Sambaqui Santa Marta II, Laguna, SC, has not yet been dated, Electron Spin Resonance (ESR) measurements were performed in aragonite shells collected from different layers of Sambaqui Santa Marta II, starting from the base to the center of the Sambaqui. Radiocarbon analysis by Accelerator Mass Spectrometry (AMS) at Beta Analytic laboratory were also performed for comparison with ESR results. Before measurements, shells were chemically etched, after drying, were pulverized and sieved. The sediments were separated into small portions which were irradiated with gamma radiation from a 60Co source with doses from 5 up to 120 Gy. Ages around 2,000 to 4,000 years have been obtained. The results obtained are consistent with the dates of others Sambaquis of the region, possibly were built at the same time.

Resolving species boundaries in the Atlanta brunnea species group (Gastropoda, Pterotracheoidea).

Atlantid heteropods are a family of holoplanktonic marine gastropods that occur primarily in tropical and subtropical latitudes. Atlantids bear a delicate aragonitic shell (<14 mm) and live in the upper ocean, where ocean acidification and ocean warming have a pronounced effect. Therefore, atlantids are likely to be sensitive to these ocean changes. However, we lack sufficiently detailed information on atlantid taxonomy and biogeography, which is needed to gain a deeper understanding of the consequences of a changing ocean. To date, atlantid taxonomy has mainly relied on morphometrics and shell ornamentation, but recent molecular work has highlighted hidden diversity. This study uses an integrated approach in a global analysis of biogeography, variation in shell morphology and molecular phylogenies based on three genes (CO1, 28S and 18S) to resolve the species boundaries within the Atlanta brunnea group. Results identify a new species, Atlanta vanderspoeli, from the Equatorial and South Pacific Ocean, and suggest that individuals of A. brunnea living in the Atlantic Ocean are an incipient species. Our results provide an important advance in atlantid taxonomy and will enable identification of these species in future studies of living and fossil plankton.

Oyster larvae as a potential first feed for small-mouthed ornamental larval fish

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:657-669 (2019) - DOI: https://doi.org/10.3354/aei00338 Oyster larvae as a potential first feed for small-mouthed ornamental larval fish Alexander J. Basford*, Benjamin Mos, Tomoki Mishina, Symon A. Dworjanyn National Marine Science Centre, Southern Cross University, Coffs Harbour, NSW 2450, Australia *Corresponding author: alex.basford@scu.edu.au ABSTRACT: Aquaculture of ornamental marine fish for the aquarium trade is a possible solution to the negative environmental impacts of wild collection. An impasse to the culture of many marine fish species is high larval mortality due to unsuitable live feeds. Common live feeds can be too large for ornamental species, which often have larvae with small mouths. We tested wild oyster larvae as an alternative live feed for first-feeding blue tang Paracanthurus hepatus. P. hepatus readily consumed oyster larvae but did not consume rotifers. Survival and growth of P. hepatus fed oyster larvae was similar to unfed controls, likely due to the oyster trochophores developing into indigestible veligers. Restricting the diet of P. hepatus to only oyster trochophores improved survival and eye development, but survival rates remained low. Oyster trochophores were conditioned in pH 4.8 seawater to compromise their aragonite shells, and P. hepatus fed these had higher survival at 5 d post-hatch (dph) compared to those fed untreated trochophores and were the only fish surviving to 10 dph. The high consumption rates of oyster larvae by P. hepatus highlight the potential for bivalve larvae to be used as live feeds for first-feeding larval fish. Further research into improving the nutritional value of oyster larvae for larval fish may improve their viability as first feeds. KEY WORDS: Acidification · Blue tang · Paracanthurus hepatus · Fatty acids · Live feeds · Larval rearing Full text in pdf format Supplementary material Corrections to supplement PreviousNextCite this article as: Basford AJ, Mos B, Mishina T, Dworjanyn SA (2019) Oyster larvae as a potential first feed for small-mouthed ornamental larval fish. Aquacult Environ Interact 11:657-669. https://doi.org/10.3354/aei00338 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: December 05, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.

Turritelline mass accumulations from the Lower Miocene of southern Germany: implications for tidal currents and nutrient transport within the North Alpine Foreland Basin

The mass occurrence of turritelline gastropod shells from the Lower Miocene of southern Germany allows for detailed studies of their palaeoecology, transport mechanisms, preservation potentials and the reconstruction of nutrient regimes. Changes in the fabric of the gastropod-dominated beds are used to reconstruct a generally deepening environment corresponding to the Lower Miocene transgression within the Upper Molasse Sea of the North Alpine Foreland Basin. The sedimentary succession ranges from chaotically arranged, densely packed and near-shore transported; wave-influenced deposits showing bimodal shell orientations; more widely dispersed shells showing a uni-directional orientation; and dispersed shells showing diverse orientations. The shells often show damage to the apex and aperture though it is not clear whether this is due to predation events, pagurisation or abrasion due to transport. An outstanding feature is the replacement of aragonite shells by calcite leading to internal vugs as well as modulating the outer shell surface morphology. The high density of turritelline gastropods indicates a nutrient-rich palaeoenvironment at the northern edge of the Molasse Sea.

Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals

Abstract. Here we present a comprehensive attempt to correlate aragonitic Na∕Ca ratios from Desmophyllum pertusum (formerly known as Lophelia pertusa), Madrepora oculata and a caryophylliid cold-water coral (CWC) species with different seawater parameters such as temperature, salinity and pH. Living CWC specimens were collected from 16 different locations and analyzed for their Na∕Ca ratios using solution-based inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements. The results reveal no apparent correlation with salinity (30.1–40.57 g kg−1) but a significant inverse correlation with temperature (-0.31±0.04 mmolmol-1∘C-1). Other marine aragonitic organisms such as Mytilus edulis (inner aragonitic shell portion) and Porites sp. exhibit similar results highlighting the consistency of the calculated CWC regressions. Corresponding Na∕Mg ratios show a similar temperature sensitivity to Na∕Ca ratios, but the combination of two ratios appears to reduce the impact of vital effects and domain-dependent geochemical variation. The high degree of scatter and elemental heterogeneities between the different skeletal features in both Na∕Ca and Na∕Mg, however, limit the use of these ratios as a proxy and/or make a high number of samples necessary. Additionally, we explore two models to explain the observed temperature sensitivity of Na∕Ca ratios for an open and semi-enclosed calcifying space based on temperature-sensitive Na- and Ca-pumping enzymes and transport proteins that change the composition of the calcifying fluid and consequently the skeletal Na∕Ca ratio.

A 45-year sub-annual reconstruction of seawater temperature in the Bay of Brest, France, using the shell oxygen isotope composition of the bivalve Glycymeris glycymeris

A reconstruction of sea surface temperature (SST) spanning 45 years (1966–2011) was developed from δ18O obtained from the aragonitic shells of Glycymeris glycymeris, collected from the Bay of Brest, France. Bivalve sampling was undertaken monthly between 2014 and 2015 using a dredge. In total, 401 live specimens and 243 articulated paired valves from dead specimens were collected, of which 24 individuals were used to reconstruct SST. Temperatures determined using the palaeotemperature equation of Royer et al. compared well with observed SST during the growing season between 1998 and 2010 (Pearson’s correlation: p = 0.002, r = 0.760). Furthermore, a significant negative correlation was found between the reconstructed SST and the North Atlantic Subpolar Gyre (SPG) index ( p = 0.001, r = −0.50), and a significant positive correlation was found with the East Atlantic Pattern (EAP) index when the reconstructed SST was lagged by 1 year ( p = 0.002, r = 0.46). This led to the conclusion that EAP and SPG are major influences on SSTs in the Bay of Brest. As the SPG controls air temperature in Northern Europe and the EAP controls water temperature in Southern Europe, this suggests that the Bay of Brest is an interaction area between these two climate systems. As such, this locality is interesting as the δ18O of the shells can be used as a proxy for both the SPG and EAP, and temperature reconstructions can provide a unique insight into how these climate systems interacted prior to the instrumental era.

Trophodynamics of Southern Ocean pteropods on the southern Kerguelen Plateau.

Pteropods are a group of small marine gastropods that are highly sensitive to multiple stressors associated with climate change. Their trophic ecology is not well studied, with most research having focused primarily on the effects of ocean acidification on their fragile, aragonite shells. Stable isotopes analysis coupled with isotope‐based Bayesian niche metrics is useful for characterizing the trophic structure of biological assemblages. These approaches have not been implemented for pteropod assemblages. We used isotope‐based Bayesian niche metrics to investigate the trophic relationships of three co‐occurring pteropod species, with distinct feeding behaviors, sampled from the Southern Kerguelen Plateau area in the Indian Sector of the Southern Ocean—a biologically and economically important but poorly studied region. Two of these species were gymnosomes (shell‐less pteropods), which are traditionally regarded as specialist predators on other pteropods, and the third species was a thecosome (shelled pteropod), which are typically generalist omnivores. For each species, we aimed to understand (a) variability and overlap among isotopic niches; and (b) whether there was a relationship between body size and trophic position. Observed isotopic niche areas were broadest for gymnosomes, especially Clione limacina antarctica, whose observed isotopic niche area was wider than expected on both δ13C and δ15N value axes. We also found that trophic position significantly increased with increasing body length for Spongiobranchaea australis. We found no indication of a dietary shift toward increased trophic position with increasing body size for Clio pyramidata f. sulcata. Trophic positions ranged from 2.8 to 3.5, revealing an assemblage composed of both primary and secondary consumer behaviors. This study provides a comprehensive comparative analysis on trophodynamics in Southern Ocean pteropod species, and supports previous studies using gut content, fatty acid and stable isotope analyses. Combined, our results illustrate differences in intraspecific trophic behavior that may be attributed to differential feeding strategies at species level.

Degradation of Internal Organic Matter is the Main Control on Pteropod Shell Dissolution After Death

AbstractThe potential for preservation of thecosome pteropods is thought to be largely governed by the chemical stability of their delicate aragonitic shells in seawater. However, sediment trap studies have found that significant carbonate dissolution can occur above the carbonate saturation horizon. Here we present the results from experiments conducted on two cruises to the Scotia Sea to directly test whether the breakdown of the organic pteropod body influences shell dissolution. We find that on the timescales of 3 to 13 days, the oxidation of organic matter within the shells of dead pteropods is a stronger driver of shell dissolution than the aragonite saturation state of seawater. Three to four days after death, shells became milky white and nano scanning electron microscope images reveal smoothing of internal surface features and increased shell porosity, both indicative of aragonite dissolution. These findings have implications for the interpretation of the condition of pteropod shells from sediment traps and the fossil record, as well as for understanding the processes controlling particulate carbonate export from the surface ocean.

Ocean acidification may alter predator-prey relationships and weaken nonlethal interactions between gastropods and crabs

Predator–prey interactions often drive ecological patterns and are governed by factors including predator feeding rates, prey behavioral avoidance, and prey structural defenses. Invasive species can also play a large ecological role by disrupting food webs, driving local extinctions, and influencing evolutionary changes in prey defense mechanisms. This study documents a substantial reduction in the behavioral and morphological responses of multiple gastropod species (Nucella lapillus, N. ostrina, Urosalpinx cinerea) to an invasive predatory crab (green crab Carcinus maenas) under ocean acidification conditions. These results suggest that climate-related changes in ocean chemistry may diminish non-lethal effects of predators on prey responses including behavioral avoidance. While snails with varying shell mineralogies were similarly successful at deterring predation, those with primarily aragonitic shells were more susceptible to dissolution and erosion under high CO2 conditions. The varying susceptibility to predation among species with similar ecological roles could indicate that the impacts of invasive species like green crabs could be modulated by the ability of native and invasive prey to withstand ocean acidification conditions.

Polarized mapping Raman spectroscopy: identification of particle orientation in biominerals

Abstract The identification of the texture of biominerals and the particle orientation in the bivalve shells of Anodonta cygnea was performed using polarized Raman spectroscopy mapping measurements. A single crystal of aragonite served as a reference to disclose orientational information on the mesoscopic scale. The relative intensities of different Raman modes combined with the determination of depolarization ratio of the Ag Raman mode at 1087 cm−1 of an aragonite single crystal was used to indicate the angular variation of aragonite crystallites in biominerals. The imaging technique shows that the a- and b-axis of aragonite crystallites in both, nacreous and prismatic layers do not only have one orientation but they are organized in a domain-type arrangement. The angular divergence in the prismatic layer of the shells is larger and hence, the crystallites in the nacreous layer have a higher degree of co-orientation. Results provide relevant textural information about aragonitic shells and indicate a sensitive technique to evaluate the crystal orientation in biominerals.

Determination of the temperature of precipitation of aragonite in shells of Anadara brasiliana (Lamarck, 1819) from Playa Norte, Cazones de Herrera (Holocene, Veracruz, Mexico) by means of trace element analysis

In this work, data on the precipitation temperatures of aragonite were evaluated from the analysis of three shells of the bivalve species Anadara brasiliana (Lamarck, 1819). The material was collected in the locality known as Playa Norte, belonging to the municipality of Cazones de Herrera, Veracruz, Mexico.The LA-ICP-MS method was applied to determine the concentrations of the elements Mg, Sr and Li in the calcareous matrix of the shells, in order to assess their distribution along them, and to obtain values of the temperature of precipitation of aragonite, taking into account the arrangement of the clear and dark bands of the shell. Concurrently, 25 oxygen stable isotope values were determined for the shells via mass spectrometry to obtain quantitative data regarding the same variable. Finally, the values obtained by both methods were compared. Temperature data from Sr/Li ratios vary between 22.48 °C and 25.39 °C, while δ18O temperatures range from 26.2 °C and 33.1 °C. Sr/Li temperatures are in strong agreement with data from the Coastal Ocean Observation Lab (COOL), while δ18O are not. Possible causes for this include the influence of salinity and evaporation rates on δ18O values for the Gulf of Mexico. We conclude that the analysis of the Sr/Li ratio via LA-ICP-MS can be applied reliably to obtain data of precipitation temperatures in this bivalve species, and subsequently in other bivalve species from the Gulf of Mexico. δ18O is not a reliable proxy for interpreting temperature values in bivalves from this basin. In addition, we come to the conclusion that Sr/Li ratios can be effectively used as δ18O-independent temperature proxies for biogenic aragonite.

Aptian carbonate platform development in the Southern Iberian Palaeomargin (Prebetic of Alicante, SE Spain)

The Aptian stratigraphic record of the Alicante region consists of: a rudist and coral-rich carbonate platform of earliest Aptian age (Llopis Formation), with a discontinuous siliciclastic member at its top; followed by late Early, to Late Aptian hemipelagic marls and marlstones (Almadich Formation); and then by renewed carbonate platform development of Late Aptian to earliest Albian age (Seguilí Formation). In the Llopis Formation, SW-dipping, massive clinoform beds of bioclastic debris are succeeded by flat-lying platform-top beds. The latter show a cyclically regressive stacking of biofacies, with rudist-dominated floatstone in their lower parts passing upwards to finer-grained, more sparsely fossiliferous bed tops with burrow mottling. Caprinid rudists, with originally almost wholly aragonitic shells, dominate the external platform-top facies, while more internal facies contain a mix of monopleurid, polyconitid and requieniid rudists, all with relatively slightly thicker development of the calcitic outer shell layer, together with caprinids. Biostratigraphic and carbon-isotope data link the termination of the Llopis platform with the onset of OAE1a. The carbonate platform of the Seguilí Formation again contains tabular platform-top beds showing repeated cyclic regression, with dense rudist and/or chondrodont floatstones overlain by sparser floatstones with wackestone matrix and secondarily filled burrows. But caprinids are now absent, while requieniids and polyconitids, some of large size, as well as radiolitids, all with thickened calcitic outer shell layers, accompany the tubular monopleurid, Mathesia, together with a greater development of Chondrodonta biofacies. The same overall pattern of biotic turnover from the Early, to the Late Aptian is confirmed in other parts of Iberia and contiguous regions. Moreover, Iberian platforms of late Early Aptian age outside the present study area reveal a transitional phase with an increasing proportion of polyconitids in the outer platform-top to upper slope facies at the expense of caprinids. The siliciclastic influx at the top of the Llopis Formation implies a climatic shift from arid, to relatively more humid/pluvial conditions through the mid-Early Aptian, as seen in several other Iberian sections. This climatic change was probably forced by the intensified greenhouse conditions at the onset of OAE1a. By contrast with these Iberian platforms, caprinids continued to dominate the outer platform-top zones of some central to southern Tethyan platforms until the close of the Early Aptian. This broad palaeolatitudinal differentiation of rudist associations within the Tethyan belt implies a climatic influence, whether exerted through thermal modulation of seawater pH and/or aragonite saturation, variation in nutrient flux, or any combination of these.

Caught in the act? Distraction sinking in ammonoid cephalopods

Two specimens of the Late Mississippian ammonoid cephalopod Metadimorphoceras sp. were recovered from the Bear Gulch Limestone in Montana. This unit was deposited in the lowest part of the Big Snowy Basin, where the bottom waters are thought to have been strongly oxygen deficient. The two nearly equally sized specimens are impressions with soft tissues preserved as brown carbonaceous smears. Diagenetic processes destroyed their aragonitic shells. The preserved soft tissues are interpreted as mandibles, remains of food in the crop, and, possibly, ovaries and eyes. The specimens are on their sides, aperture-to-aperture, and probably the male is on the left and the female is on the right. The specimens are thought to have been in the process of copulation when they died. Copulation by most (all?) externally shelled cephalopods (extinct ammonoids and fossil and extant nautiloids) was probably in a head-to-head, aperture-to-aperture position. This was probably governed in part by restricted accessibility to the female reproductive organs due to the presence of the shell and the ability of both animals to partly withdraw into their shells during copulation. The shell protected them from predators during copulation. In coleoids, which lack an external shell, copulation is a more rapid affair due to the greater vulnerability from predators including other coleoids. We suggest that the fossils from the Bear Gulch Limestone and similar finds of paired ammonoids preserved together with interlocking apertures, and including soft parts in the body chamber, represent examples of ammonoid behavior frozen in time. The two ammonoids were probably too pre-occupied with copulation to notice that they were sinking into the hypoxic bottom waters of the basin and facing suffocation (distraction sinking).

Impact of preservation techniques on pteropod shell condition

Pteropods have been a key focus of ocean acidification studies during the last decade due to their fragile aragonite shells and key role they play in polar ecosystems. Pteropods collected at sea are typically preserved before analysis at onshore laboratories. Despite the importance placed on pteropods as a sentinel for the impact of ocean acidification on marine calcifiers, there has never been a systematic study assessing how different preservation techniques affect the condition of pteropod shells. In this study we perform an experiment to assess the impact of six preservation techniques on the shell condition of Limacina retroversa pteropods. Using five shell condition-assessment methods, we find shells that were air dried were the least altered relative to the time of collection. Of the solution-based preservation techniques, shells were least altered when preserved in 70% buffered ethanol and most altered in a solution of sodium chloride buffered formalin. Our results have implications for the interpretation of pteropod shell condition in samples which have been stored in solution, and provide guidelines for the preservation of future pteropod collections.

Microstructures in relation to temperature-induced aragonite-to-calcite transformation in the marine gastropod Phorcus turbinatus.

Mollusk shells represent important archives for paleoclimatic studies aiming to reconstruct environmental conditions at high temporal resolution. However, the shells, made of calcium carbonate in the form of aragonite and /or calcite, can be altered through time which may undermine the suitability for any reconstruction based on geochemical proxies (i.e., stable isotopes, radiocarbon). At present, the diagenetic processes involved in this chemical and physical deterioration are still poorly understood. The present study aims to shed light on the onset and development of diagenetic alteration in the aragonitic shell of Phorcus turbinatus. To artificially mimic diagenesis, shells of P. turbinatus were exposed to elevated temperatures. The transformation of the mineral phase was monitored by means of Confocal Raman Microscopy whereas the structural changes were investigated using Scanning Electron Microscopy and Atomic Force Microscopy. The results indicate that the two distinct shell layers (prismatic layer and nacre) respond differently to the elevated temperatures, suggesting that the different microstructural organization and organic content may drive the onset and spread of the aragonite-to-calcite transformation. Furthermore, changes in the microstructural arrangement became visible prior to the mineralogical transition. Our results demonstrate that the specific physico-chemical characteristics of structurally different areas within the biogenic carbonates have to be taken into account when studying the phase transformation occurring during diagenesis.

Palaeoecology of Chondrodonta (Bivalvia) from the lower Aptian (Cretaceous) Apulia Carbonate Platform (Gargano Promontory, southern Italy)

Chondrodonta is a Cretaceous oyster-like bivalve with a predominantly calcitic, dorso-ventrally elongated and slightly inequivalve shell. In the Tethyan carbonate platforms this taxon occurs commonly in rudist-bearing limestone. Often preserved with still articulated valves, the opportunistic Chondrodonta had a cemented and gregarious life habit. In the Apulia Carbonate Platform (Gargano Promontory, southern Italy), Chondrodonta beds occur within lower Aptian lagoonal to platform–basin margin deposits. The studied Chondrodonta concentrations, which recorded the early evolutionary phase and spreading of this bivalve, are made up of specimens ascribed to Chondrodonta glabra Stanton. In the inner platform the meter-thick Chondrodonta accumulations were originated by autochthonous bouquet-like valve aggregates, frequently preserved in living position. These aggregates constitute superimposed carpets characterized by only a few generations which were affected by mass mortality and rapid burial processes. These mass mortalities were related to repeated environmental lethal fluctuations that occurred at the onset of the early Aptian OAE 1a. The quick fluctuations of the Chondrodonta populations are typical of unstable and unpredictable environments characterized by significant changes in trophic resources and hyperthermal and acidification peaks. The studied Chondrodonta specimens show different shell preservation according to their palaeobathymetric location. In the shallow-water inner platform specimens the internal aragonite shell layer was rapidly dissolved while in deeper-water margin ones it was preserved during the early diagenetic phases. This different preservation is interpreted as related to different aragonite saturation state of shallow seawater, and tentatively connected to the acidification peak that occurred at the onset of the early Aptian OAE 1a.

Calcium isotope evidence that the earliest metazoan biomineralizers formed aragonite shells

Calcium isotope evidence that the earliest metazoan biomineralizers formed aragonite shells

Effects of elevated CO2 on shell 13C and 18O content and growth rates in the clam Scapharca broughtonii

The effects of elevated CO2 levels on growth and stable carbon and oxygen isotope compositions (δ13C and δ18O) of aragonitic shells were experimentally evaluated by rearing the bloody clam, Scapharca broughtonii, at two different temperatures and at six different pCO2 levels (17 °C: 269, 382, 550, 757, 939, and 1114 µatm; 25 °C: 332, 463, 653, 872, 1137, and 1337 μatm). Ambient CO2 levels did not much affect shell growth rates. Mass spectrometric analysis of the outer shell layer indicated a negative correlation between seawater pH and shell δ18O (equivalently, a positive correlation between seawater pCO2 and shell δ18O) at both temperatures (regression slopes: −0.70‰ ± 0.14‰/pH unit at 17 °C; −0.36‰ ± 0.17‰/pH unit at 25 °C). A positive correlation was observed between seawater pH and shell δ13C at both temperatures, but the regression slopes were less steep than those between seawater pH and the δ13C of seawater DIC. As CO2 levels rose (and pH dropped to about 7.6), shell δ18O and δ13C increased relative to ambient dissolved inorganic carbon (DIC). Both approached apparent isotopic equilibrium in acidified waters. Shell δ18O was below that of the ambient mix of bicarbonate and carbonate ions, and usually below apparent isotopic equilibrium with water. Kinetic discrimination against heavy isotopes during CO2 hydration and hydroxylation reactions may contribute to this isotopic “enlightenment”, and elevated ambient CO2 may “wash out” this effect. Our findings thus generally support models of calcification physiology and shell isotopic content, and have implications for isotopic paleontology.

Equilibrated clumped isotope signatures of land-snail shells observed from laboratory culturing experiments and its environmental implications

This study reports on the clumped isotope values (Δ47) of land-snail shells precipitated at known temperatures ranging from 20 °C to 30 °C. Our observed shell Δ47 values fall into the uncertainties of published Δ47–T calibration line (e.g. Kelson et al., 2017), indicating the shell aragonite of land snails is precipitated at clumped isotopic equilibrium without an obvious Δ47 vital effect. The Δ47 data are neither related to the various bulk isotopic input sources (both for δ13C and δ18O) which result from differences in the supplied food and water; nor are they related to the ingested carbonate composition or snail growth rate. Furthermore, we preliminarily applied the Δ47–T calibration (Kelson et al., 2017) to calculate the mean growth temperatures of the parent snails. Results suggest that the clumped isotope values for land-snail shells can be regarded as a useful tool to reconstruct the mean seasonal temperature of snail activity when the environmental parameters are optimum. Future studies should focus on the applicability of this relationship to snails in natural environments where the self-preservation or acclimatization mechanisms are more complex.

Mechanisms to Explain the Elemental Composition of the Initial Aragonite Shell of Larval Oysters

AbstractCalcifying organisms face increasing stress from the changing carbonate chemistry of an acidifying ocean, particularly bivalve larvae that live in upwelling regions of the world, such as the coastal and estuarine waters of Oregon (USA). Arguably the first and most significant developmental hurdle faced by larval oysters is formation of their initial prodissoconch I (PDI) shell, upon which further ontological development depends. We measured the minor metal compositions (Sr/Ca, Mg/Ca) of this aragonitic PDI shell and of post‐PDI larval Crassostrea gigas shell, as well as the water they were reared in, over ∼20 days for a May and an August cohort in 2011, during which time there was no period of carbonate under‐saturation. After testing various methods, we successfully isolated the shell from organic tissue using a 5% active chlorine bleach solution. Elemental compositions (Sr, Mg, C, N) of the shells post‐treatment showed that shell Sr/Ca ranged from 1.55 to 1.82 mmol/mol; Mg/Ca from 0.60 to 1.11 mmol/mol, similar to the few comparable published data for larval oyster aragonite compositions. We compare these data in light of possible biomineralization mechanisms: an amorphous calcium carbonate (ACC) path, an intercellular path, and a direct‐from‐seawater path to shell formation via biologically induced inorganic precipitation of aragonite. The last option provides a mechanistic explanation for: (1) the accelerated precipitation rates of biogenic calcification in the absence of a calcifying fluid; (2) consistently elevated precipitation rates at varying ambient‐water saturation states; and (3) the high Ca‐selectivity of the early larval calcification despite rapid precipitation rates.