Carbon- and oxygen-isotope composition of the cuttlebone of Sepia officinalis: a tool for predicting ecological information?

Analysis of the isotope composition of calcareous structures of marine organisms has proved useful in providing biological data. The present study constitutes the first detailed work undertaken on the isotope composition of coleoid cephalopods. We analysed the carbon- and oxygen-isotope composition [δ¹³C (CO²⁻ ₃) and δ¹⁸O (CO²⁻ ₃), respectively] of the cuttlebone aragonite of wild and cultivated specimens of Sepia officinalis Linnaeus, 1758. δ¹³C (CO²⁻ ₃) ranged from −2.94 to 1.00‰, δ¹⁸O (CO²⁻ ₃) from −0.18 to 2.08‰. The carbon-isotope composition is not in equilibrium with the carbon species of the ambient seawater, and does not reflect the deposition of CaCO₃ in seawater. The potential influence of environmental factors and biological processes on the carbon-isotope composition of the cuttlebone is discussed. In contrast to δ¹³C, the oxygen-isotope composition of cuttlebone aragonite appears to be in isotopic equilibrium with the ambient seawater. Seasonal changes in isotopic temperature revealed by our analyses agreed with changes in the temperature of the ambient seawater. CaCO₃ was deposited all year round. A maximum life span of 2 yr, a year-round spawning season, and variable growth rates among and within individuals have been inferred from the isotopic temperatures. Received: 14 April 1998 / Accepted: 26 November 1998     

Differential increment-deposition rate in embryonic statoliths of the loliginid squid Loligo vulgaris

 Apart from one study that reported growth of less than one increment per day in statoliths of the squid Alloteuthis subulata, most studies so far have presumed that one increment was laid down per day in the statoliths of the squid species they examined. The present study provides evidence of differential daily growth rates in embryonic statoliths of the squid Loligo vulgaris Lamarck, 1798, thus confirming a previous report for A. subulata. Incremental growth rates of L. vulgaris statoliths differ as a function of temperature. Squid embryos were incubated in the laboratory at three temperatures (12.0, 15.5 and 21.1 °C), and tetracycline staining was used to follow statolith growth. This growth slowed in squid exposed to the lowest temperature, but recovered when the squid were returned to warm conditions, indicating statolith adaptation. Statolith growth rate after incubation at 12 °C was 1.3% d⁻¹ and reached 6.1% d⁻¹ for squids exposed to 21.1 °C. Statoliths from embryos incubated at 15.5 °C yielded a rate of 1 increment d⁻¹ and a mean daily growth of 2.2 μm in the dorsal dome area of the statolith. In contrast, the slow growth of statoliths incubated at 12 °C yielded a mean daily growth of only 0.9 μm in the dorsal dome and the readings resulted in a less-than-daily increment-deposition rate. Received: 9 October 1999 / Accepted: 30 March 2000     

Habitat and age of the giant squid (<Emphasis Type="Italic">Architeuthis sanctipauli</Emphasis>) inferred from isotopic analyses

The age and habitat of the giant squid, Architeuthis sanctipauli Velain, 1877, were determined based on isotopic analyses of the statoliths of three female specimens captured off Tasmania, Australia, between January and March 1996. Assuming that the aragonite of the statoliths formed in equilibrium with seawater, ¹⁸O analyses indicated that the squid lived at temperatures of 10.5–12.9°C, corresponding to average depths of 125–250 m and maximum depths of 500 m. The capture records indicated that these squid may have occasionally ranged still deeper, to as much as 1000 m. All the statoliths were labeled with bomb ¹⁴C (¹⁴C=+22.9 to +44.6), consistent with the depths inferred from ¹⁸O. A thin section through one of the statoliths revealed 351 growth increments grouped into check-ring structures every 10–16 increments. A model for statolith growth and the pattern of temporal change in ¹⁴C in the water column was used to estimate the ages of the three specimens. These estimates were very sensitive to the choice of depth range over which ¹⁴C values were integrated. Assuming that the capture depths represented the maximum habitat depths of these individuals, the calculations suggested an age of 14 years or less. More refined age estimates require a better understanding of the variation of ¹⁴C and temperature with depth in the areas in which the squids live.Communicated by J.P. Grassle, New Brunswick     

Clean electrochemical deposition of calcium carbonate to prevent scale formation in cooling water systems

Calcium carbonate (CaCO₃) deposited in water systems leads to scale formation, decreases flow rate, reduces heat transfer and favors microbial proliferation of toxic bacteria such as Legionella. This issue may be solved by electrochemical deposition, without adding toxic chemicals. Therefore, we studied here the deposition of CaCO₃ by electrochemical reduction of oxygen into hydroxide ions with stainless steel and titanium (Ti) working electrodes. Analysis was done using cyclic voltammetry, chronoamperometry, dynamic impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDX) coupled with X-ray diffraction (XRD). Results show that optimal formation of CaCO₃ is done at ?1.2 V with the stainless steel electrode and at ?1.4 V for the Ti electrode. More negative potentials induce the formation of calcite. Using the Ti electrode, we found that aragonite is the major form (82 %), with only one capacitive loop. Using the stainless steel electrode at 1.2 V, we found 47 % of aragonite and 38 % of calcite. Overall, our findings demonstrate the feasibility of the electrochemical deposition of CaCO₃ in cooling water systems, without the addition of any chemical.     

Influence of temperature on the microstructure of statoliths of the thumbstall squid Lolliguncula brevis

 A laboratory study investigating the influence of temperature on the microstructure of statoliths of Lolliguncula brevis is described. Groups of squid were subjected to various temperature regimes for periods in excess of 30 d. Statoliths extracted from 20 squid were examined using a confocal microscope in laser scanning mode. The parts of the statoliths deposited during the course of the experiments were identified using either putative daily increment counts or from checks produced in response to capture and handling. These checks appear to consist of a series of prominent increments rather than reflecting a period of interrupted statolith growth. Increments deposited during the experiment generally displayed reduced contrast and clarity in comparison to the “wild” parts of the statolith, presumably in response to the constant conditions imposed in the laboratory. Average statolith growth rates observed over the course of the experiment showed a strong positive relationship to ambient temperature. A significant sex effect was apparent, with statoliths of female squid generally growing faster than those of males. Observed statolith growth rates at 15 °C were generally below 1 μm d⁻¹, suggesting that the widths of daily increments produced under these conditions may approach the resolution limits of a light microscope. The implications for studies using increment numbers to estimate age are discussed. Received: 23 July 1999 / Accepted: 17 February 2000     

Trophic niche overlap among dolphinfish and co-occurring tunas near the northern edge of their range in the western North Atlantic

We present the first quantitative analyses of dolphinfish (Coryphaena hippurus) foraging habits and trophic interactions with co-occurring yellowfin (Thunnus albacares) and albacore (T. alalunga) tunas in the Southern New England region of the western North Atlantic Ocean. Fish caught by recreational anglers in offshore waters of Massachusetts were sampled during the summers of 2007–2010. Diet analysis revealed that shortfin squid (Illex illecebrosus) and small pelagic crustaceans were principal prey to dolphinfish, yellowfin tuna, and albacore tuna. A wide variety of Sargassum-associated fishes were also important to dolphinfish and yellowfin tuna diets. Dietary (Schoener’s index: 0.82–0.86) and isotopic niche (isotopic ellipse overlap: 53.6–64.7 %) overlap was high, and dolphinfish and tunas occupied equivalent trophic positions (TP = 3.4–3.6). Relative prey size in dolphinfish and yellowfin tuna diets exhibited convergence with ontogeny. Overall, dolphinfish had the greatest isotopic niche width, which was twice as large as yellowfin tuna and three times as large as albacore tuna; dolphinfish also consumed the greatest range of prey sizes. Results quantify dolphinfish trophic interactions in the western Atlantic near the northern extent of their geographical range, and are relevant for ecosystem-based management of the offshore pelagic guild in the context of shifting fish populations and fisheries in response to climate and ecological change.     

Effect of temperature on statolith growth of the European squid Loligo vulgaris during early life

Over the past decade, statolith interpretation has resulted in a major advance in our knowledge of squid population-dynamics, but the way in which environmental conditions affect the statolith increment-deposition ratio remains virtually unknown. The object of the present study was to determine the effect of temperature on this process, using tetracycline marks to validate statolith growth in Loligo vulgaris Lamarck, 1798 under rearing conditions equivalent to severe winter (11 °C) and summer (19 °C) temperature regimes. Tetracycline marking was performed every 10 d (at 10, 20, 30, 40, 50 and 60 d of age). The newly hatched squid paralarvae were slightly smaller in summer than those hatched in winter. Survival rates were similar in both cultures, but growth rates (wet mass) of summer squids were double those in winter. At hatching, statoliths were already longer in the summer squids, and growth rates were 2% d⁻¹ as opposed to 0.9% d⁻¹ for winter statoliths. For the dorsal dome area of the statolith, where more increment counts were made, statolith growth was of 3.25 μm d⁻¹ in summer, and daily increment deposition was confirmed in 87% of the statoliths. The slow growth of statoliths at winter temperatures yielded a mean growth of 1.1 μm d⁻¹– insufficient to discern the increments using light microscopy. Subsequent SEM observation enabled only 21% of the winter statoliths to be read; these also indicated a deposition rate of one increment d⁻¹. Since the life span of L. vulgaris is ≃1 yr, squids will experience at least one winter during their life cycle, and this might be visible on the statolith. Received: 28 June 1999 / Accepted: 20 December 1999     

Oxygen and carbon isotopic composition of fish otoliths

Oxygen and carbon isotopic composition of the aragonite of fish otoliths was measured on 175 specimens comprising 24 different species in 1989 and 1990. All specimens but two came from the northern Adriatic Sea or the northern Tyrrhenian Sea (two freshwater specimens were studied for comparison with the marine fish). The data obtained confirm the results of previous research suggesting the existence of equilibrium conditions between the otolith aragonite and ambient water with respect to ·¹⁸O(CO₃ ^2-) values. Examination of one of the species indicated that the CaCO₃ of otoliths probably accumulates continuously over time, seasonal isotopic changes being clearly visible (from a set of radial spot samples) for both oxygen and carbon isotopes. The apparent isotopic equilibrium with ambient water suggests that the ¹⁸O(H₂O) of the endolymph is equal to that of seawater and considerably different from that of fish body water. In the case of ¹³C(CO₃ ^2-), isotopic equilibrium with dissolved carbon species in seawater is never reached, even though the contribution of metabolic CO₂ is variable among different species and even among different individuals of the same species. This rules out the possibility of using ¹³C(CO₃ ^2-) values obtained from fossil otoliths for paleoenvironmental and paleobiological conclusions.     

Elevated CO2 alters larval proteome and its phosphorylation status in the commercial oyster, Crassostrea hongkongensis

Ocean acidification (OA) is beginning to have noticeable negative impact on calcification rate, shell structure and physiological energy budgeting of several marine organisms; these alter the growth of many economically important shellfish including oysters. Early life stages of oysters may be particularly vulnerable to OA-driven low pH conditions because their shell is made up of the highly soluble form of calcium carbonate (CaCO₃) mineral, aragonite. Our long-term CO₂ perturbation experiment showed that larval shell growth rate of the oyster species Crassostrea hongkongensis was significantly reduced at pH < 7.9 compared to the control (8.2). To gain new insights into the underlying mechanisms of low-pH-induced delays in larval growth, we have examined the effect of pH on the protein expression pattern, including protein phosphorylation status at the pediveliger larval stage. Using two-dimensional electrophoresis and mass spectrometry, we demonstrated that the larval proteome was significantly altered by the two low pH treatments (7.9 and 7.6) compared to the control pH (8.2). Generally, the number of expressed proteins and their phosphorylation level decreased with low pH. Proteins involved in larval energy metabolism and calcification appeared to be down-regulated in response to low pH, whereas cell motility and production of cytoskeletal proteins were increased. This study on larval growth coupled with proteome change is the first step toward the search for novel Protein Expression Signatures indicative of low pH, which may help in understanding the mechanisms involved in low pH tolerance.     

Oxygen and carbon isotope profiles from Nassa mutabilis shells (Gastropoda): accretion rates and biological behaviour

Six shells of the Gastropoda species Nassa mutabilis L. were collected in the Adriatic Sea at a depth of a few metres off the central Italian coast during 1996 and 1997. The oxygen and carbon isotope composition of spot samples collected from the shell apex to the top was measured according to well-established techniques. The results obtained allow the following conclusions: (1) the CaCO₃ of the N. mutabilis shells is essentially formed by aragonite as proved by X-ray diffraction measurements; (2) the CaCO₃ is precipitated under isotope equilibrium conditions or very close to equilibrium with the environmental water; (3) shell accretion takes place all year round, although the warm period is preferred since the accretion rates are higher during the warm half of the year and considerably reduced in winter; (4) the carbon isotope composition changes according to the age of the specimen, probably in relation to changes in its nutritional regimen; and (5) the alternation of warm and cold periods recorded by the shells allows the evaluation of their age and of the season of their birth and death. Received: 3 December 1998 / Accepted: 7 September 1999     

Geographic variation in statolith trace elements of the Humboldt squid, Dosidicus gigas, in high seas of Eastern Pacific Ocean

We applied the solution-based inductively coupled plasma mass spectrometry to quantify trace elements in statoliths of Humboldt squid, Dosidicus gigas, collected from the high seas off Chile, Peru, and Costa Rica by Chinese squid jigging vessels during 2007–2009. All squid samples were aged and their spawning dates were back-calculated based on daily increments in statoliths. The most abundant trace elements in the whole statolith were Ca and Sr followed by other elements in the order of Fe, Mg, Zn, Ba, Cu, Mn, Ni, Al, Cr, Co, and U. Significant differences in Mn and Sr were found among samples from the three regions. Sr, Ni, Mn, and Co contributed significantly to the discrimination among the regions, with Co responsible for explaining most of the variation, followed by Ni, Mn, and Sr. Squid from the high seas off Costa Rica could be separated from those off Peru and Chile mostly due to the differences in Ni, Sr, and Co, while samples off Peru and Chile could be distinguished mainly because of differences in Mn and Co. Discriminant function analysis suggested that the overall cross-validated classification rate was 85.6 % with samples off Chile having the highest correct identification rates and samples off Costa Rica having the highest false classification rates. Significant positive relationships were found between sea surface temperature (SST) and Cr/Ca, Mn/Ca, and U/Ca, and there was a negative relationship between SST and Cu/Ca, Sr/Ca. This study suggests that the spatial difference in trace elements of statolith can be used to separate geographic populations of D. gigas and that elements having significant relationships with SST can be considered as natural indicators of ambient temperature.     

Stable isotopes changes in the adductor muscle of diseased bivalve Ruditapes philippinarum

In this article, we show how a disease could bias stable isotope analyzes of trophic networks and propose a strategy in the choice of tissues to be analyzed. In the past few years, a new pathology (brown muscle disease or BMD) affecting the posterior adductor muscle of Ruditapes philippinarum has emerged in Arcachon Bay. BMD induces a necrosis of muscle tissues which become infused by conchiolin and hence calcified. As muscle of mollusks are often used for trophic food webs studies through stable isotopic analyzes, this work investigated the effect of BMD on carbon and nitrogen isotopic ratios of anterior and posterior adductor muscles of clams collected in February and August 2007. Infected clams displayed a lower condition index and a posterior adductor muscle δ¹³C enrichment of 1.2‰ in February and 0.7‰ in August. δ¹⁵N of posterior muscles was however not affected by the disease. Anterior muscle of diseased clams remained healthy and displayed the same isotopic signature as both posterior and anterior muscular tissues of healthy clam. Acidification significantly depleted δ¹³C in posterior muscles of infected clams, suggesting calcification, contrary to anterior muscles of infected clam and to both muscles of healthy clams, where no effect was observed. An X-ray diffractometry analysis confirmed the presence of CaCO₃ (aragonite). Trophic food web studies relying on stable isotope ratios should utilize only healthy animals or anterior adductor muscles when expertise in mollusk pathology is lacking.     

Combined sclerochronologic and oxygen isotope analysis of gastropod shells (Gibbula cineraria, North Sea): life-history traits and utility as a high-resolution environmental archive for kelp forests

The grey top-shell, Gibbula cineraria is a common member of temperate to cold water kelp forest communities, but its longevity and the age structure of its populations remains unresolved. Combined measurements of shell growth rates (sclerochronology) and oxygen isotope composition allow analysis of rate and timing of shell growth. Eight specimens were analyzed from the southern North Sea (near Helgoland, German Bight). Three age groups were identified but external measurements (width, height, ornamentation patterns and number of whorls) and shell weight are not adequate for ontogenetic age discrimination. Stable oxygen isotope data is consistent with shell growth during the interval from April to December in isotopic equilibrium with seawater, and growth increments exhibit strong tidal controls with fortnightly bundles well preserved. Reliable environmental proxy data (water temperature) can be extracted from the shell aragonite using conventional stable oxygen isotope analyses, with a temporal resolution of days attainable during intervals of maximum growth, but annual extremes are not always recorded in the shell. While demonstrating the utility of G. cineraria as a environmental and potential paleoenvironmental proxy for kelp forest habitats, its longevity has been significantly overestimated.     

Strontium/Calcium ratios in statoliths of the neon flying squid, Ommastrephes bartrami (Cephalopoda), in the North Pacific Ocean

Strontium to calcium ratios were observed along longitudinal sections of statoliths of nine neon flying squid, Ommastrephes bartrami (LeSueur, 1821), including three mature females (422 to 454 mm mantle length, ML; 207 to 306 d old) obtained from the North Pacific (27–35°N; 144–150°E) during winter and six immature males and females (187 to 226 mm ML; 126 to 164 d old) collected from 39°N; 145°E and 39°N; 169°W during summer. The distances between the nucleus (core) and the edge of the dorsal dome were approximately 660 to 690 μm in mature females and 450 to 510 μm in the immature squid. Sr/Ca ratios were determined at intervals of 30 μm between the nucleus and edge of the dorsal dome. Sr/Ca ratios were higher in areas near the nuclei and peripheral portions of the dorsal dome than in the middle portions of the statoliths (270 to 420 μm from the nuclei, corresponding to ages of 60 to 90 d) in mature females; thus a U-shaped pattern was evident. Sr/Ca ratios in the six immature squid decreased from nucleus to the dorsal dome; in three squid the ratios slightly increased toward the dorsal dome edge. The observed Sr/Ca ratios in immature squid were considered to represent younger portions of the U-shaped pattern. In the present study we discuss this pattern in relation to environmental and biological conditions of O. bartrami, which undertakes seasonal migrations between spawning grounds in the Subtropical Domain and feeding grounds in the Subarctic Domain and Transitional Zone in the North Pacific Ocean. Although Sr/Ca ratios are potentially affected by ambient water temperature and ontogenetic conditions, including somatic growth and statolith growth, it was impossible to evaluate each environmental and biological effect separately, as variations in these factors are complicated and effects could be interdependent. Received: 11 April 1997 / Accepted: 27 December 1997     

Molecular structure and composition of fish otoliths

Recent and fossil otoliths from 25 different fishes have been studied for their amino acid content and for their C¹³/C¹² and O¹⁸/O¹⁶ distribution in the carbonate fraction. The selection includes specimens from a wide phylogenetic range as well as from various freshwater and marine habitats. All otoliths are composed of aragonite, and their total organic matter ranges from 0.2 to 10%. The organic matter is a protein (MW>150,000), which is characterized by a high abundance of acidic amino acids. In comparison to molluscs that exhibit a wide variety of different mineralized tissues which are species specific, the proteinaceous matter of all otoliths is chemically rather uniform. The high abundance of oxygen-rich amino acids accounts for the ease of mineralization of the organic template. Namely, oxygen supplied by carboxyl grops is used for the coordination of Ca⁺⁺ ions, resulting in the formation of metal ion coordination polyhedra. Carbonate groups linked via hydrogen bridges to the template will exchange their oxygen with that of the metal polyhedra to stabilize the structure; Ca⁺⁺O₉ polyhedra are the consequence. Subsequent nucleation and crystal growth will lead to aragonite. Oxygen and carbon isotope data indicate that the aragonite is formed close to isotopic equilibrium with the sea. This is surprising, because seawater has no direct access to the inner ear where the otolith orginates. Isotope data may serve a threefold purpose: (1) to determine the mean water temperature where the fish lived, (2) to distinguish between fresh water and marine fish in ancient deposits, and (3) to reveal information on migrtory tendencies of fish.Contribution No. 2214 from the Woods Hole Oceanographic Institution.     

Precipitation of aragonite by calcitic bivalves in Mg-enriched marine waters

To understand the relative importance of biological versus physicochemical control over biomineralization, we have tested if the chemical composition of the medium (i.e., the Mg/Ca ratio) can change the mineralogy of mollusk shells. The shells of mollusks are made of calcite and/or aragonite, which are by far the most common CaCO₃ polymorphs. Several species of bivalves with predominantly calcitic shells have been cultivated in artificial seawater with a Mg/Ca molar ratio within the range of 8.3–9.2, well above the present value for seawater (5.2). Four out of six species used (the scallop Chlamys varia, the oyster Ostrea edulis, the saddle oyster Anomia ephippium and the mussel Mytilus edulis) survived long enough to secrete significant amounts of calcium carbonate. The deposits (sometimes extensive) formed on the interior shell surfaces were predominantly aragonitic. Three individuals of C. varia also increased their length by adding new shell at the margin. Contrary to the internal shell deposits, these margins were high-Mg calcite. This implies that the marginal mantle is able to exert a more strict control on the secreted mineral phase than the mantle facing the internal shell surface. This is the first report on an in vivo experimentally forced switch in bivalve shell mineralogy, from calcite to aragonite due to a change in water chemistry.     

Calcium and magnesium carbonate concentrations in different growth regions of gorgonians

Four of the most abundant gorgonian species from the southwestern Cape waters, Eunicella papillosa (Esper, 1797), E. alba (Esper, 1797), E. tricoronata Velimirov, 1971 and Lophogorgia flamea (Ellis and Solander, 1786) were analysed for Ca and Mg by atomic absorption spectroscopy (AAS) and ethylenediaminetetraacetate (EDTA) titration. The total mineral content in the peripheral tissues, excluding the axial skeleton, expressed as the sum of CaCO₃ and MgCO₃ of dry matter was between 65.5 and 83.5%. The mineral content varied in different growth regions and all specimens showed a higher degree of mineralization at the base than at the branch tips. The MgCO₃ concentration varied with genus and species and was between 9 and 11 mol %. The variation of the MgCO₃ concentration within different growth regions of the same species was small and generally did not exceed 0.8 mol %. From the branch to the stem, CaCO₃ and total mineral content was found to increase. The CaCO₃:MgCO₃ rations in different growth regions of all species indicated that the composition of the mesoskeleton with regard to the relative concentration of CaCO₃ and MgCO₃ is constant throughout the animal. Mineralogically, the mesoskeleton consists of high magnesian calcite as identified by X-ray diffraction. MgCO₃ concentrations determined by the peak shift method and by AAS were in fair agreement. The MgCO₃ data in gorgonian samples from the cold Atlantic Ocean and the warmer Indian Ocean show a linear relationship between water temperature and MgCO₃ concentration already demonstrated by Chave (1954). However, our data were consistently lower by 1 to 2% than expected.     

The utility of statoliths and bell size to elucidate age and condition of a scyphomedusa (Cassiopea sp.)

Scyphomedusae play important roles in marine ecosystems and are of economic significance. However, no reliable techniques for estimating scyphomedusa age have been documented. This study focused on the utility of Cassiopea sp. (Cnidaria: Scyphozoa) statoliths, statocysts, and body size as proxies for age of medusae. Reared medusae of known age and a manipulative experiment were used to assess the accuracy and reliability of four measures of age: number of statoliths, size (diameter) of statoliths, area of statocyst (housing statoliths), and bell diameter. Bell diameter provided the most accurate measure of age under constant conditions, but was increasingly inaccurate under varying environmental conditions. In contrast, the average number of statoliths per medusa reflected age with relatively low accuracy, but did not vary with changes in food availability and salinity. Only temperature influenced the average number of statoliths. Comparisons of bell diameter to the number of statoliths in medusae under low food availability to those fed well showed that the ratio of medusa size to the number of statoliths can be used to recognise medusae that are relatively poorly conditioned. Statoliths, therefore, provide a tool for studying both population ecology and the influence of environmental variation on medusa growth.     

Stable isotope ratio variations in non-scleractinian coelenterate carbonates as a function of temperature

Some coelenterates of the class Hydrozoa and some anthozoan coelenterates from the subclass Octocorallia secrete skeletons of calcium carbonate. Skeletal carbonates of three hydrozoans and of two octocorals were analyzed for the stable isotopes of carbon and oxygen. The results suggest that each of these coelenterates deposits CaCO₃ in oxygen isotopic equilibrium with seawater, and that at least one octocoral, Heliopora, has skeletal carbon in apparent isotopic equilibrium with atmospheric CO₂. Two of these coelenterates, Millepora and Helipora, are significant contributors to the construction of coral reefs. Whereas ¹⁸O of these corals is temperature dependent, ¹³C is not obviously related to temperature. The ¹⁸O-temperature relationship is not significantly different from the oxygen isotope paleotemperature scale developed by Epstein et al. (1953). These findings contrast with numerous analyses of the carbonate in scleractinian coelenterates, which have long been reported to deposit CaCO₃ skeletons whose carbon and oxygen isotopic compositions are not in equilibrium with the external sea-water environment.     

A morphological and structural study of the larval shell from the abalone <Emphasis Type="Italic">Haliotis tuberculata</Emphasis>

The larval shell of the marine gastropod Haliotis tuberculata was investigated by polarised light microscopy, scanning electron microscopy, Raman microspectroscopy and infra-red spectroscopy. Trochophore and veliger larval sections were used for histological examination of the growing shell and each larval stage was related to the shell development and the appearance of calcified formations. We determined the stage of initial calcification by specific staining combined with polarised light examination. The shell of 30-h-old pre-veliger larvae was found to be mineralized, confirming that calcification occurred before larval torsion. Using both infra-red and Raman spectroscopy, we showed that CaCO₃ deposition occurred at the pre-veliger stage and that the mineral phase initially deposited was essentially composed of aragonite.