Shell Growth Rate Research Articles

Interannual to decadal variability of summer sea surface temperature in the Sea of Okhotsk recorded in the shell growth history of Stimpson's hard clams (Mercenaria stimpsoni)

Sclerochronological and shell stable oxygen isotopic analyses were conducted on live-caught specimens of Stimpson's hard clams, Mercenaria stimpsoni, from the southern Sea of Okhotsk, off northern Hokkaido, Japan. In this region, the main growing season of this species during early ontogeny (below the age of 12years) lasts from mid-spring to mid-fall at sea surface temperatures (SST) between approximately 10 and 22°C. Growth cessation begins between late fall and early spring at SST, below approximately 6°C; however, shell growth was largely limited to the summer season later in life. Counting of annual increments indicated that this species had a relatively long life span of up to 100years. Annual shell growth rates were high during early ontogeny and declined abruptly afterwards. Mean standardized shell growth indices (SGIs) of long-lived specimens were positively correlated to the mean summer SSTs near the sampling site and in the coastal waters off northern Hokkaido. The SGI chronology of the longest-lived specimen (99years old) exhibited periodicities of approximately 10 and 5years during the calendar years 1920–2011, possibly reflecting the quasi-decadal variability of summer SST in the southern Sea of Okhotsk. These findings indicate that M. stimpsoni could serve as an archive to reconstruct past marine climate changes in the Sea of Okhotsk.

Growth performance and feed utilization of Haliotis tuberculata coccinea (Reeve) juveniles from the Azores (north-eastern Atlantic Ocean): An assay of three mono algae diets

ABSTRACTWe assessed the dietary value of available seaweeds (Ulva lactuca, Ulva intestinalis, and Sargassum vulgare) as food for juvenile abalone Haliotis tuberculata coccinea. During the 6 weeks that the experiment lasted, initial shell length and weight increased from 13.95 ± 0.32 mm to 15.30 ± 0.30 mm and from 0.39 ± 0.02 g to 0.47 ± 0.03 g. Ulva lactuca diet resulted in higher shell growth rate (58.47 ± 16.76 μm day−1), SGR (1.15 ± 0.47%.day−1), weight gain (65.5% ± 33.3), and PER (1.56 ± 0.31), possibly thanks to its higher crude protein content. Both green algae (U. lactuca, U. intestinalis) prove to support the growth of H. tuberculata coccinea. However, they might not be appropriate for an optimal intensive aquaculture production; further research should be conducted to find more efficient diets for juvenile abalone.

Effects of translocation on survival and growth of freshwater mussels within a West Gulf Coastal Plain river system

Abstract Human‐mediated threats have led to the rapid decline of species inhabiting freshwater ecosystems, and among the groups most affected are freshwater mussels of the family Unionidae. As a result, species translocation is increasingly used in conservation programmes, yet experimental evidence documenting the success of this strategy is limited. The goal of this study was to examine the effects of translocation on survival probability, shell growth and body condition of a state‐threatened (Quadrula houstonensis) and common (Amblema plicata) species of freshwater mussel in the San Saba River, located in a West Gulf Coastal Plain river system, USA. Survival probability estimated from a joint live and dead encounter model was high (> 0.85) and varied by treatment for both species. However, differences in survival probability between resident and transplant treatments were relatively small for A. plicata (0.01) and Q. houstonensis (0.12). Generalized additive mixed models of yearly proportional growth and linear mixed models of Fulton's K index for A. plicata varied by treatment and were lower in transplant treatments. Shell growth of Q. houstonensis was unaffected by translocation; whereas, Fulton's K was higher in the transplant treatment. Methods used to translocate mussels were important factors leading to high survival and limited impacts to shell growth and body condition in this study. Differences in shell growth rate between treatments are attributed to possible differences in habitat quality between sites. Our results demonstrate that A. plicata and Q. houstonensis are tolerant of translocation, despite the broad assumption that translocation is detrimental to mussels. Thus, there is a continuing need to study species' responses to translocation to test and improve the ecological soundness of this strategy, particularly because climate change and other human stressors will exacerbate the need to implement conservation measures such as translocation in future decades.

Calibration of the B/Ca proxy in the planktic foraminifer Orbulina universa to Paleocene seawater conditions

AbstractThe B/Ca ratio of planktic foraminiferal calcite, a proxy for the surface ocean carbonate system, displays large negative excursions during the Paleocene‐Eocene Thermal Maximum (PETM, 55.9 Ma), consistent with rapid ocean acidification at that time. However, the B/Ca excursion measured at the PETM exceeds a magnitude that modern pH calibrations can explain. Numerous other controls on the proxy have been suggested, including foraminiferal growth rate and the total concentration of dissolved inorganic carbon (DIC). Here we present new calibrations for B/Ca versus the combined effects of pH and DIC in the symbiont‐bearing planktic foraminifer Orbulina universa, grown in culture solutions with simulated Paleocene seawater elemental composition (high [Ca], low [Mg], and low total boron concentration ([B]T). We also investigate the isolated effects of low seawater [B]T, high [Ca], reduced symbiont photosynthetic activity, and average shell growth rate on O. universa B/Ca in order to further understand the proxy systematics and to determine other possible influences on the PETM records. We find that average shell growth rate does not appear to determine B/Ca in high calcite saturation experiments. In addition, our “Paleocene” calibration shows higher sensitivity than the modern calibration at low [B(OH)4−]/DIC. Given a large DIC pulse at the PETM, this amplification of the B/Ca response can more fully explain the PETM B/Ca excursion. However, further calibrations with other foraminifer species are needed to determine the range of foraminifer species‐specific proxy sensitivities under these conditions for quantitative reconstruction of large carbon cycle perturbations.

High dietary quality of non-toxic cyanobacteria for a benthic grazer and its implications for the control of cyanobacterial biofilms

BackgroundMass occurrences of cyanobacteria frequently cause detrimental effects to the functioning of aquatic ecosystems. Consequently, attempts haven been made to control cyanobacterial blooms through naturally co-occurring herbivores. Control of cyanobacteria through herbivores often appears to be constrained by their low dietary quality, rather than by the possession of toxins, as also non-toxic cyanobacteria are hardly consumed by many herbivores. It was thus hypothesized that the consumption of non-toxic cyanobacteria may be improved when complemented with other high quality prey. We conducted a laboratory experiment in which we fed the herbivorous freshwater gastropod Lymnaea stagnalis single non-toxic cyanobacterial and unialgal diets or a mixed diet to test if diet-mixing may enable these herbivores to control non-toxic cyanobacterial mass abundances.ResultsThe treatments where L. stagnalis were fed non-toxic cyanobacteria and a mixed diet provided a significantly higher shell and soft-body growth rate than the average of all single algal, but not the non-toxic cyanobacterial diets. However, the increase in growth provided by the non-toxic cyanobacteria diets could not be related to typical determinants of dietary quality such as toxicity, nutrient stoichiometry or essential fatty acid content.ConclusionsThese results strongly contradict previous research which describes non-toxic cyanobacteria as a low quality food resource for freshwater herbivores in general. Our findings thus have strong implications to gastropod-cyanobacteria relationships and suggest that freshwater gastropods may be able to control mass occurrences of benthic non-toxic cyanobacteria, frequently observed in eutrophied water bodies worldwide.

Temporal Variation in Shell Growth Rate of CockleAnadara granosain Relation with its Reproductive Cycle

A study was conducted on the relationship between the reproductive cycle and shell growth rate of Anadara granosa (Linnaeus, 1758). Gonadal maturity stages, increment width, and environmental factors were examined by means of a field enclosure experiment in Balik Pulau, Penang Island, Malaysia, from December 2011 to November 2012. Histological analysis of gonads showed that gametogenic activity of A. granosa occurred throughout the year, with maximum spawning activity observed from April 2012 to late June 2012 (15%–28%) in males and from March 2012 to late June 2012 (19%–44%) in females. Shell cross-section analysis showed that the increment widths of both sexes in the growing group (indeterminate and developing stages) and the spawning group (ripe and spawning stages) ranged from 35–57 to 8–17 µm, respectively. Seawater temperature and salinity recorded on a daily basis throughout the study period ranged from 22–33°C and 29–31, respectively. A comparison of increment width and gonad development stages in different environmental conditions showed that shell growth in the growing group decreased when seawater temperature and salinity decreased slightly. In contrast, increment widths in the spawning group were much narrower and were influenced by energy consumption during ripe and spawning stages. This study shows spawning breaks in shell structure are considered markers for identifying the period of sexual maturity. Therefore, spawning breaks are suitable proxies for interpretation of the temporal changes in shell microgrowth lines in terms of reproductive cycle of cockle and understanding the number of spawning periods throughout the year.

Oxygen isotopes from limpet shells: Implications for palaeothermometry and seasonal shellfish foraging studies in the Mediterranean

Limpet shells are common components of many archaeological sites in the Mediterranean. To test whether δ18O values from archaeological Patella caerulea shells can serve as a reliable palaeothermometer for the Mediterranean and a reliable archive of season of collection information, we collected live P. caerulea from eight Mediterranean locations in Croatia, Israel, Libya, Malta, Tunisia, and Turkey. Shell growth patterns were studied in section, and samples for oxygen isotope analysis were milled from the shells and used to calculate sea surface temperature (SST). As with other species of limpet, SST reconstructed from P. caerulea δ18O values were lower than expected from observational records. However, when a correction factor of −0.72‰ was applied, the shells recorded SST within the range of instrumental SST. SST calculated from δ18Oshell values of the most recently formed shell portion of monthly-collected shells from one site in Libya were strongly and significantly correlated with instrumental SST in the region (R2=0.95). Oxygen isotope curves from individual shells sampled at high resolution from each of the study sites across the Mediterranean exhibited sinusoidal patterns. Annual growth lines correlated with the lowest δ18Oshell values and were thus formed in summer. However, shell growth rates varied markedly between the sites. Some sites with larger shells recorded less than a year of growth in broad, highly irregularly shaped increments. At other sites, medium sized shells recorded several years of growth with clear, regular growth increments. A sclerochronological approach can therefore be used to pre-screen limpet shell sections before geochemical sampling. The δ18Oshell values from shells sampled at high-resolution recorded the full seasonal range of instrumental SST at each collection site. This reinforces the potential of this species as one of the few sub-seasonal resolution palaeoenvironmental archives in the region. Additionally, the pattern of δ18Oshell variation from the last formed shell portion was studied to determine whether accurate season of collection information could be identified from P. caerulea shells. The correct season was interpreted >80% of the time indicating that this species is a good candidate for seasonal shellfish foraging studies using archaeological shells.

Reproductive performance of one-year-old Pacific abalone (Haliotis discus hannai) and its crossbreeding effect on offspring growth and survival

The Pacific abalone (Haliotis discus hannai) is one of the most popular farming mollusks in China, where three- to four-year-old adults are used as broodstock for commercial seeding. However, no reports exist regarding the reproduction performance of one-year-old Pacific abalone and its potential use in commercial breeding. In this study, one line of one-year-old abalone (AO) and two lines of three-year-old abalone (BD and HD), which were selected for rapid growth for three or six generations, were adopted to establish three purebred groups (AO, BD and HD) and two crossbred groups (BDAO and HDAO). The performance of these five groups on embryonic development, growth and survival rate was evaluated. According to the results, the average yolk diameter of oocytes produced by one-year-old abalone was significantly smaller than that produced by three-year-old individuals. The fertilization rate of the AO group was significantly higher than those of the other four groups, while the metamorphosis rate was the opposite. During the first 40d, the average shell growth rate of the AO group was slower than those of the other four groups, while the average shell length of this group was greatest after 120d. The AO group also showed a significantly higher survival rate than those of other groups during the period from 38d to 160d post fertilization. No significant differences were found in the embryonic development parameters or shell growth rates between the purebred and crossbred groups that shared the same dam line. However, the survival rates of the crossbred groups were significantly higher than those of the purebred groups. These results suggest that one-year-old Pacific abalone could be used as broodstock for reproduction and that an accelerated breeding cycle may enhance commercial genetic improvement programs.

Shell Growth Performance of Hatchery Produced Pinctada margaritifera: Family Effect and Relation with Cultured Pearl Weight

Size is the most important and valuable quality trait of cultured pearls produced by the black-lipped pearl oyster, Pinctada margaritifera. In French Polynesia, several breeding programmes have been started that aim to improve this size trait, which is highly related to shell growth rate in both recipient and donor oysters. Shell growth rate dictates the time of grafting, size of implanted nuclei and bio-mineralisation potential of the mantle and pearl sac. We assessed shell growth rate through routine digital shell biometric analysis on 22 hatchery families produced between 2005 and 2008. These included full-sib families and half-sib families derived from polyandry (one dam crossed with two or more sires). Results showed that: 1) a significant family effect was recorded for growth performance, analysed according to the Von Bertalanffy model, 2) a significant male effect was observed for some of the half-sib families and 3) a relationship was found between the shell growth performances of five families randomly selected and used as graft donors in a grafting experiment and the final weight of the cultured pearls produced. These results have important implications for the breeding of pearl oysters with high growth capacities: it may be possible to select oyster lines for the potential to produce large pearls using shell equivalent diameter estimated by the digital method as a selection criterion.

Survival and growth rate of pen shell Atrina lischkeana spats with various substrates and densities in suspended intermediate culture

Survival and growth rate of pen shell <I>Atrina lischkeana</I> spats with various substrates and densities in suspended intermediate culture

Assessing elemental ratios as a paleotemperature proxy in the calcite shells of patelloid limpets

Archaeological shell and fish middens are rich sources of paleoenvironmental proxy data. Patelloid limpet shells are common constituents in archaeological middens found along European, African, and South American coastlines. Paleotemperature reconstructions using oxygen isotope ratios of limpet shells depend on the ability to constrain the oxygen isotope ratio of seawater; therefore, alternative proxies are necessary for coastal localities where this is not possible. The study evaluates whether Mg/Ca, Sr/Ca, Li/Ca, Li/Mg, and Sr/Li ratios are reliable proxies of sea surface temperature (SST) in the calcite layer of shells of the patelloid limpets, Patella vulgata and Nacella deaurata. We compare Mg/Ca, Sr/Ca, Li/Ca, Li/Mg, and Sr/Li ratios to the seasonal variations in contemporaneous δ18Oshell values, which primarily record seasonal changes in SST. Elemental ratios (Mg/Ca, Sr/Ca, Li/Ca, Li/Mg, and Sr/Li) show no significant correlations with reconstructed SST in P. vulgata and N. deaurata shells, nor do they show sinusoidal cycles expected from a SST proxy. In addition, shell δ13C values show no significant ontogenetic trends, suggesting that these limpets exhibit little change in metabolic carbon incorporation into the shell with increasing ontogenetic age. Although shell growth rate exhibits a logarithmic decrease with age based on calculated linear extension rates, growth rate does not correlate with elemental profiles in these limpets. Overall, elemental ratios are not reliable recorders of paleotemperature in patelloid limpets.

A key to the past? Element ratios as environmental proxies in two Arctic bivalves

Understanding rapid climate change in the Arctic and its ecosystem implications requires more information on the environment at temporal resolutions and time-periods not available from instrumental records. Such information can be acquired through geochemical proxy records, but sub-annual records are rare. We analyzed shell material of bivalve mollusks (Serripes groenlandicus and Ciliatocardium ciliatum) placed on oceanographic moorings for one year in two Arctic fjords to assess the potential use of shell elemental ratios as environmental proxies. Li/Ca, Mg/Ca, Li/Mg, Li/Sr, Mn/Ca, Sr/Ca, Mo/Ca, and Ba/Ca were determined using Laser-Ablation Inductively-Coupled-Plasma Mass-Spectrometry. Combining data from moorings with previously derived sub-annual shell growth models allowed us to relate the elemental ratio patterns to oceanographic parameters (temperature, salinity, and fluorescence). Shell Ba/Ca profiles were characterized by abrupt peaks occurring 11 to 81days after the phytoplankton bloom, as indicated by an index of seawater fluorescence. Li/Ca and Mg/Ca values exhibited significant logarithmic relationships with shell growth rate, indicated by marginal R2 values of 0.43 and 0.30, respectively. These ratios were also linearly related to temperature, with marginal R2 values of 0.15 and 0.17, respectively. Mn/Ca and Sr/Ca ratios exhibited variability among individuals and their temporal pattern was likely controlled by several unidentified factors. Mo/Ca patterns within the shells did not demonstrate correlations with any of the oceanographic parameters. Our results reflect complex relationships between elemental ratios and bivalve metabolism, methodological limitations, as well as contemporaneous environmental processes, suggesting that none of the studied elemental ratios can be used as unequivocal proxies of seawater temperature, salinity, paleoproductivity, or shell growth rate. Despite this, Ba/Ca and Li/Ca can be used as sub-annual temporal anchors in further studies because the variability of these elements was synchronized in each fjord.

Insights from sodium into the impacts of elevated pCO2 and temperature on bivalve shell formation

Ocean acidification and warming are predicted to affect the ability of marine bivalves to build their shells, but little is known about the underlying mechanisms. Shell formation is an extremely complex process requiring a detailed understanding of biomineralization processes. Sodium incorporation into the shells would increase if bivalves rely on the exchange of Na+/H+ to maintain homeostasis for shell formation, thereby shedding new light on the acid-base and ionic regulation at the calcifying front. Here, we investigated the combined effects of seawater pH (8.1, 7.7 and 7.4) and temperature (16 and 22°C) on the growth and sodium composition of the shells of the blue mussel, Mytilus edulis, and the Yesso scallop, Patinopecten yessoensis. Exposure of M. edulis to low pH (7.7 and 7.4) caused a significant decrease of shell formation, whereas a 6°C warming significantly depressed the rate of shell growth in P. yessoensis. On the other hand, while the amount of Na incorporated into the shells of P. yessoensis did not increase in acidified seawater, an increase of Na/Cashell with decreasing pH was observed in M. edulis, the latter agreeing well with the aforementioned hypothesis. Moreover, a combined analysis of the shell growth and sodium content provides a more detailed understanding of shell formation processes. Under acidified conditions, mussels may maintain more alkaline conditions favorable for calcification, but a significant decrease of shell formation indicates that the mineralization processes are impaired. The opposite occurs in scallops; virtually unaffected shell growth implies that shell mineralization functions well. Finding of the present study may pave the way for deciphering the mechanisms underlying the impacts of ocean acidification and warming on bivalve shell formation.

Manganese in the shell of the bivalve Mytilus edulis: Seawater Mn or physiological control?

Manganese in the shell calcite of marine bivalves has been suggested to reflect ambient seawater Mn concentrations, thus providing a high-resolution archive of past seawater Mn concentrations. However, a quantitative relationship between seawater Mn and shell Mn/Ca ratios, as well as clear understanding of which process(es) control(s) shell Mn/Ca, are still lacking. Blue mussels, Mytilus edulis, were grown in a one-year duration field experiment in the Menai Strait, U.K., to study the relationship between seawater particulate and dissolved Mn2+ concentrations and shell calcite Mn/Ca ratios.Shell Mn/Ca showed a well-defined intra-annual double-peak, with maximum values during early spring and early summer and low values during autumn and winter. Seawater particulate Mn peaked during winter and autumn, with a series of smaller peaks during spring and summer, whereas dissolved Mn2+ exhibited a marked single maximum during late-spring to early-summer, being low during the remainder of the year. Consequently, neither seawater particulate Mn nor dissolved Mn2+ concentrations explain the intra-annual variation of shell Mn/Ca ratios.A physiological control on shell Mn/Ca ratios is evident from the strong similarity and timing of the double-peaked intra-annual variations of Mn/Ca and shell growth rate (SGR), the latter corresponding to periods of increased metabolic activity (as indicated by respiration rate). It is thus likely that in M. edulis SGR influences shell Mn/Ca by altering the concentration or activity of Mn2+ within the extra-pallial fluid (EPF), by changing the flux of Mn into or the proportion of protein bound Mn within the EPF. By linking shell Mn/Ca ratios to the endogenous and environmental factors that determine growth and metabolic activity, this study helps to explain the lack of a consistent relationship between shell Mn/Ca in marine bivalve shell calcite and seawater particulate and dissolved Mn2+ concentrations.The use of Mn content from M. edulis shell calcite as a proxy for the dissolved and/or particulate Mn concentrations, and thus the biogeochemical processes that control them, remains elusive.

Intraspecific variations in shell calcification across thermal window and within constant temperatures: Experimental study on an intertidal gastropod Monetaria annulus

The relationship between temperature and shell growth was examined by rearing an intertidal cowrie species, Monetaria annulus (Gastropoda, Cypraeidae), at seven constant temperatures between 21°C and 34°C over four experimental years. Data on shell growth were collected during the callus-building stage, in which calcification exclusively occurs around the spiral shell constructed in the juvenile stage. Our experiments elucidated some clear trends among temperatures, although careful consideration is required to interpret the results obtained under the potential confounding factors between temperature and experimental year. Calcification was accelerated by increasing temperature in the range between 21°C and 33°C, and drastically slowed down at 34°C probably due to heat stress. No relationship was found between body size and callus growth rates. The duration of callus-building indicated a negative exponential relationship with rearing temperature. However, no simple relationship was found between temperature and final shell thickness; the final shell thickness described two peaks around 21°C and 30°C. This finding strongly suggests that a physiological control by calcifiers cannot be ignored to explain the thermal response of calcification rates. Our results also suggest that considering the thermal seasonality as well as the difference in mean temperature, is required to explain the negative latitudinal clines in shell thickness frequently observed in molluscan species. We also focused on the variation among the individuals reared at the same temperatures. Statistical analyses suggested that the final shell thickness and the duration of calcification were better described by the normal and lognormal distributions, respectively. The distribution of shell growth rates did not considerably deviate from the normal distribution with respect to skewness and kurtosis. However, their heteroscedasticity among temperatures was inherent and significant; its variance positively depended not on the mean but on temperature. The observed pattern might be an evidence that possible stabilization selection on calcification rates is more relaxed at warmer temperatures.

Biomineralization changes with food supply confer juvenile scallops (Argopecten purpuratus) resistance to ocean acidification.

Future ocean acidification (OA) will affect physiological traits of marine species, with calcifying species being particularly vulnerable. As OA entails high energy demands, particularly during the rapid juvenile growth phase, food supply may play a key role in the response of marine organisms to OA. We experimentally evaluated the role of food supply in modulating physiological responses and biomineralization processes in juveniles of the Chilean scallop, Argopecten purpuratus, that were exposed to control (pH ~ 8.0) and low pH (pH ~ 7.6) conditions using three food supply treatments (high, intermediate, and low). We found that pH and food levels had additive effects on the physiological response of the juvenile scallops. Metabolic rates, shell growth, net calcification, and ingestion rates increased significantly at low pH conditions, independent of food. These physiological responses increased significantly in organisms exposed to intermediate and high levels of food supply. Hence, food supply seems to play a major role modulating organismal response by providing the energetic means to bolster the physiological response of OA stress. On the contrary, the relative expression of chitin synthase, a functional molecule for biomineralization, increased significantly in scallops exposed to low food supply and low pH, which resulted in a thicker periostracum enriched with chitin polysaccharides. Under reduced food and low pH conditions, the adaptive organismal response was to trade-off growth for the expression of biomineralization molecules and altering of the organic composition of shell periostracum, suggesting that the future performance of these calcifiers will depend on the trajectories of both OA and food supply.Thus, incorporating a suite of traits and multiple stressors in future studies of the adaptive organismal response may provide key insights on OA impacts on marine calcifiers.

Effects of ocean acidification driven by elevated CO2 on larval shell growth and abnormal rates of the venerid clam, Mactra veneriformis

The venerid clam (Mactra veneriformis Reeve 1854) is one of the main cultured bivalve species in intertidal and shallow subtidal ecosystems along the west coast of Korea. To understand the effects of ocean acidification on the early life stages of Korean clams, we investigated shell growth and abnormality rates and types in the D-shaped, umbonate veliger, and pediveliger stages of the venerid clam M. veneriformis during exposure to elevated seawater pCO2. In particular, we examined abnormal types of larval shell morphology categorized as shell deformations, shell distortions, and shell fissures. Specimens were incubated in seawater equilibrated with bubbled CO2-enriched air at (400±25)×10-6 (ambient control), (800±25)×10-6 (high pCO2), or (1 200±28)×10-6 (extremely high pCO2), the atmospheric CO2 concentrations predicted for the years 2014, 2084, and 2154 (70-year intervals; two human generations), respectively, in the Representative Concentration Pathway (RCP) 8.5 scenario. The mean shell lengths of larvae were significantly decreased in the high and extremely high pCO2 groups compared with the ambient control groups. Furthermore, under high and extremely high pCO2 conditions, the cultures exhibited significantly increased abundances of abnormal larvae and increased severity of abnormalities compared with the ambient control. In the umbonate veliger stage of the experimental larvae, the most common abnormalities were shell deformations, distortions, and fissures; on the other hand, convex hinges and mantle protuberances were absent. These results suggest that elevated CO2 exerts an additional burden on the health of M. veneriformis larvae by impairing early development.

Decoding the oxygen isotope signal for seasonal growth patterns in Arctic bivalves

Chemical and physical variations in skeletal structures of marine organisms can reflect environmental variability, forming the basis for reconstructing the conditions in which the organism lived. The successful use of these bio-archives for reconstructing seasonal environmental conditions is dependent on understanding intra-annual growth patterns and timing of their deposition within skeletal structures. We studied intra-annual shell growth patterns, as well as the timing and environmental processes associated with winter growth line deposition in two circumpolar bivalve mollusks, Serripes groenlandicus and Ciliatocardium ciliatum. Shell growth deposited during a 1-year deployment on oceanographic moorings in Kongsfjorden and Rijpfjorden, Svalbard, was analyzed in situ for δ18O values using high spatial resolution secondary ion mass spectrometry (SIMS). A new digital method was developed to measure the location of SIMS spots along chronologically deposited shell material. Dynamic time warping algorithms were adapted to align SIMS-determined δ18O values with δ18O values predicted from continuous mooring instrument recordings of seawater temperature and salinity, in order to derive intra-annual shell growth models. The resulting growth models indicated that the prominent winter growth band was formed during a slow shell growth period lasting from December until May in Kongsfjorden and from November until mid-June in Rijpfjorden. The length of the slow growth period was most likely controlled by food availability. Shell growth rate during the growing season was significantly explained by temperature (marginal R2=0.29, p<0.001) indicating that temperature partly drives shell growth rate when the food supply is sufficient. The insights into intra-annual shell growth of Arctic bivalves and the methods developed in our study are important contributions for further development of bivalve shells as proxy archives.

Is Sexual Size Dimorphism Inherent in the Scallop Patinopecten yessoensis?

Studies on sexual size dimorphism in Pectinidae are limited. This work deals with the mobile long-lived scallop Patinopecten yessoensis, a common (fished and cultured) species in the subtidal benthos of the Sea of Japan. A previously developed method of age determination in P. yessoensis allowed me to compare the parameters of same aged males and females in scallop populations. The shell growth rates and sizes of both sexes were similar; therefore, it was only possible to visually identify the sex of live specimens during the breeding period (May-June). Statistical analyses showed female-biased dimorphism in the gonad weight for age groups that are >4 years old. Gonad weight (in the prespawning period) increased with age, until a threshold age was attained, which varied between populations; and then gonad weight remained virtually unchanged. The fecundity advantage hypothesis for P. yessoensis with group mating and external fertilization is at least partly realized by physiological mechanisms, which cause older females to have larger gonads than those of same aged males in the population in order to produce a larger brood. Gregarious settlement of this bivalve contributes to the reproductive success of the population so that the energetically costly ovaries may all be fertilized.

Controls on strontium and barium incorporation into freshwater bivalve shells (Corbicula fluminea)

Trace elements of bivalve shells can potentially serve as proxies of environmental change. However, to reconstruct past environments using the geochemical properties of the shells and determine the degree to which the element levels are biologically influenced, it is essential to experimentally determine the relationship between environmental variables and the element composition of the shells. To disentangle possible controls on the incorporation of strontium and barium into freshwater bivalve shells, we conducted controlled laboratory experiments using the extremely salinity and temperature tolerant Asian clam, Corbicula fluminea as a model species. Bivalves were reared for five weeks in two sets of experiments: (1) combinations of different water temperature (10, 16 and 22°C) and food levels (0.2, 2, 4 and 8×104cells/ml) with constant Sr/Cawater (2.45mmol/mol) and Ba/Cawater (367μmol/mol) levels; and (2) combinations of different water temperature (10, 16 and 22°C) and different Sr/Cawater (ca. 4, 8 and 12mmol/mol) and Ba/Cawater levels (ca. 600, 1150 and 1500μmol/mol) with constant food level (4×104cells/ml). The Sr/Cashell ratio of C. fluminea exhibited a statistically significant negative correlation with temperature and a positive correlation to Sr/Cawater, but was not affected by changing food level or shell growth rate. On the contrary, Ba/Cashell was influenced by a complexly intertwined set of variables including temperature, food level, Ba/Cawater and shell growth rate. Partition coefficients of KDSr/Ca (0.19 to 0.29) and KDBa/Ca (0.03 to 0.19) confirmed the control of vital effects over strontium and barium incorporation into the shells. As indicated by the findings, Sr/Cashell of C. fluminea from freshwater environments can serve as a reliable proxy for past water temperature if the spatiotemporal variability of strontium-to-calcium in the water is small, well-known or can be estimated from other proxies. Interpreting Ba/Cashell values, however, is much more challenging because they are controlled by a large number of environmental and physiological variables. Sr/Cashell and Ba/Cashell of C. fluminea specimens from estuarine settings in which element-to-calcium ratios are more conservative and stable can potentially function as paleoenvironmental proxies. Findings of this study can be useful to better understand the element incorporation into shells of other bivalves including marine species.