Bivalve Mollusk Shells Research Articles

Another possible risk for the Mediterranean Sea? Aspergillus sydowii discovered in the Port of Genoa (Ligurian Sea, Italy)

Aspergillus sydowii is a cosmopolitan fungus that has been responsible for the mass destruction of coral in the Caribbean Sea over the last 15years. To our knowledge, this study has found the first case of A. sydowii in the Mediterranean Sea, in marine-bottom sediments, water and calcareous shells of bivalve molluscs sampled during a campaign to characterise the mycobiota in the Port of Genoa (Italy). The area is characterised by adverse environmental conditions (high turbidity, organic pollution and high concentrations of phosphorus and nitrogen compounds). These parameters, in combination with a rising temperature, could contribute to A. sydowii bloom and dispersal. This fungal strain may have been imported into the Port of Genoa in the bilge water of vessels or by torrent input. This work represents the first step in the implementation of a monitoring programme to safeguard calcareous sponges and sea fan corals endemic in the Mediterranean Sea.

The effect of microstructure, filler load and surface adhesion of marine bio-fillers, in the performance of Hybrid Wood-Polypropylene Particulate Bio-composite

This study aims to advance Wood-Plastic Composite materials by transferring wastes into resources, for the design and development of a low-carbon, high-value environmentally sensitive end-product, for building applications. For this purpose, four waste materials locally sourced from the Sydney Metropolitan Area were selected. Local marine litter such as Kelp brown algae (Eklonia spp.) and Bivalve mollusc shells (Veneridae spp.) are examined as combined reinforcements in the function of secondary bio-fillers. A series of 20 specimens were prepared with filler/matrix as 60/40 wt%. The blend was prepared with particle sizes sifted through 20 and 40 meshes respectively. Secondary bio-fillers are incorporated to the blend as 10 and 20 wt%. Prototype panels were manufactured by traditional hot-compression method. The filler/matrix interface was investigated, as well as the fracture surface of the bio-composite panels. The mechanical performance and moisture absorbency of the bio-composite as function of particle size, filler load and the effect of coupling agent are reported. The experimental results indicated that the novel particulate bio-composite prototypes effectively achieved an enhanced performance suitable for high-moisture environment applications.

Live-dead analysis reveals long-term response of the estuarine bivalve community to water diversions along the Colorado River

Dam construction and water diversions along the Colorado River during the twentieth century have altered the downstream estuarine ecosystem. Although it is clear that the ecosystem has changed, a lack of pre-impact studies has made it challenging to determine the magnitude and direction of change. By using a paleontological approach, we can retrospectively estimate ecological conditions in the estuary from before dam construction, particularly for benthic organisms with preservable hard parts, such as the shells of bivalve mollusks. Here, for the first time, we quantify differences in evenness, richness, taxonomic similarity, and rank-order abundance between the bivalve community living in the estuary today and two potential geohistorical baselines, the accumulated dead shells on the tidal flat and an older accumulation – known to pre-date dam construction on the river – in nearby shell-rich beach ridges called cheniers.Analysis of more than 12,000 live and dead bivalves distributed among 18 species collected from the tidal flat and cheniers on Isla Montague – an island at the mouth of the Colorado River – indicates that the pre-dam bivalve community was dominated by Mulinia modesta and was characterized by low rarified species richness and evenness (indexed by Hurlbert’s Probability of Interspecific Encounter). The increase in these metrics in the live relative to the chenier assemblage reflects a shift in the estuary from brackish to full marine conditions after damming and water diversions reduced freshwater flow to the estuary during the twentieth century. The tidal flat death assemblage was more similar to the live assemblage, which suggests that it represents post-dam construction conditions due to a large input of recent shells, whereas the chenier assemblage is an appropriate pre-impact baseline. Taxonomic similarity and rank-order abundance, indexed by Jaccard-Chao and Spearman’s Rho metrics, respectively, were too conservative to detect these differences.These baseline data, most notably the documented changes between the live and chenier assemblages, can be used to assess the efficacy of restoration efforts in the estuary, such as the Minute 319 environmental pulse flows. If restoration efforts stimulate a response in the bivalve community, metric values for evenness and richness are expected to decrease and become more similar to those we report here for the pre-impact chenier assemblage.

Reproducibility of trace element time-series (Na/Ca, Mg/Ca, Mn/Ca, Sr/Ca, and Ba/Ca) within and between specimens of the bivalve Arctica islandica – A LA-ICP-MS line scan study

Trace element time-series in bivalve mollusk shells and other (biogenic) materials can potentially serve as environmental proxies. Yet, the applicability of element-to-calcium ratios is often challenging, because non-environmental factors such as vital effects distort or mask environmental signals. If a trace element time-series is driven by an environmental factor, it should be reproducible within and between coeval specimens of the same species. In the present study, we tested whether time-series of trace element-to-calcium ratios can be reproduced within and between coeval specimens of the bivalve Arctica islandica and thus whether an external signal is encoded in the temporal variations of trace elements along the shells. We determined the concentration of sodium, magnesium, manganese, strontium and barium by means of LA-ICP-MS in line scan mode in the hinge area of seven specimens from the Isle of Man, the Gulf of Maine and Iceland. In each specimen, the element composition was determined along two replicate line scans to gauge intra-specimen reproducibility. The degree to which trace element time-series can be reproduced was inferred from linear regression analysis and equaled on average 95±4% for Ba/Ca, 82±27% for Mg/Ca, 83±18% for Sr/Ca, 74±23% for Mn/Ca, and 22±4% for Na/Ca ratios (values correspond to coefficients of determination of the linear regression analysis expressed in percent).The synchrony of Ba/Ca time-series between contemporaneous specimens from the same habitat has already been demonstrated in previous studies. Here, we observed common high-frequency variations (i.e., peaks) among coeval A. islandica from the same site for Mg/Ca, Sr/Ca, Mn/Ca and Na/Ca ratios, especially among specimens of similar ontogenetic age and with similar shell growth patterns. The results of the present study should be considered in interpretations of trace element time-series in bivalve shells as they can help to improve environmental and climate reconstructions.

Biosorption of chromium in aqueous solutions using Bivalve Mollusk Shells through central composite design (CCD) model

Pollution of water resources caused by heavy metals has been among the greatest concerns of environmentalists in recent years. Industrial wastewater contains chromium. Therefore, removing or reducing chromium from the industrial wastewater seems to be essential. In the present research, bivalve mollusk shells acted as the adsorbent. The statistical model in this research was central composite design, which analyzed the experiments. The optimal pH range for an adsorbent was about 3–5. An increase in the adsorbent dosage led to an increased efficiency. The optimal exposure time for the ion absorption mechanism of the solution was about 35 min. The absorption mechanism followed the Freundlich adsorption isotherm model. The most significant factor was found to be the independent effect of chromium initial concentration (p = 0.0007). Compared with other adsorbents such as fruit peels and the like whose availability depends on their consumption, the use of this adsorbent was economically beneficial due to its low cost and high availability.

Strontium/lithium ratio in aragonitic shells of Cerastoderma edule (Bivalvia) — A new potential temperature proxy for brackish environments

Quantitative reconstruction of water temperature from shells of bivalve mollusks is still a very challenging task. For example, in highly variable environments such as intertidal zones, shell oxygen isotope values can only provide reliable temperature estimates if the δ18Owater signature during the time of growth is known. Furthermore, trace element-to-calcium ratios such as Sr/Ca or Mg/Ca often do not serve as reliable paleothermometers, because their incorporation into bivalve shells is known to be strongly biologically controlled. Here, we present a potential novel temperature proxy which is based on the Sr/Lishell ratio of the intertidal bivalve Cerastoderma edule. Up to 81% of the variability in Sr/Lishell is mathematically explained by water temperature. It is suggested that vital effects on the incorporation of Sr and Li into the aragonitic shells are largely eliminated by normalizing Sr/Ca to Li/Ca. Growth rate does not control the incorporation of Sr or Li into the shell of C. edule. By using this new proxy, it was possible to estimate water temperature from C. edule with an uncertainty of ±1.5°C. Future studies are required to test if Sr/Lishell also serves as a reliable temperature proxy in other bivalve species and in other environments.

Coastal upwelling in Norway recorded in Great Scallop shells

AbstractThe shells of bivalve mollusks have been shown to contain a wealth of information about the environment in which the organisms lived as well as about their life histories. Shells of the Great Scallop Pecten maximus were collected in 1987 and 1988 at 15–25 m depth close to the Austevoll islands (Norway). A sharp slowdown in growth was detected in 1986 for all age classes, resulting in a growth‐rate decrease of nearly 45% over 10 d. Measurements of stable isotopes (δ18O and δ13C) in four specimens suggested that this slowdown was concurrent with a drop in water temperature. In situ measurements of environmental parameters (temperature, salinity, wind) and data from a numerical coastal model system (NorKyst‐800) confirmed that a temperature drop of 3°C occurred in July 1986 due to a sudden change in wind direction and speed along the western coast of Norway. These northerly winds parallel to the coast induced an upwelling of deep cold water along the coast. Thus, the present study demonstrated a clear relationship between regional climatic phenomena acting on an oceanographic process and the growth of a benthic invertebrate. Bivalve shells should be used to describe and characterize local upwelling events, for example, in terms of duration and intensity, in current environments and in paleoenvironments.

A new genus and species of Thyasiridae (Mollusca, Bivalvia) from deep-water, Beaufort Sea, northern Alaska.

Bivalve mollusk shells were collected in 2350 m depth in the Beaufort Sea, Arctic Ocean off northern Alaska. Initial identification suggested the specimens were a member of the bivalve family Thyasiridae, but no known eastern Pacific or Arctic living or fossil thyasirid resembled these deep-water specimens. Comparisons were made with the type of the genera Maorithyas Fleming, 1950, Spinaxinus Oliver & Holmes, 2006, Axinus Sowerby, 1821, and Parathyasira Iredale, 1930. We determined the Beaufort Sea species represents a new genus, herein described as Wallerconcha. These specimens also represent a new species, herein named Wallerconcha sarae. These new taxa are compared with known modern and fossil genera and species of thyasirds.

A Holocene palynological record from the northeastern Laptev Sea and its implications for palaeoenvironmental research

A 844 cm long core PS51/118-3 (77°53.54′ N; 132°11.92′ E) recovered from the upper slope (122 m water depth) of the Laptev Sea (Russian Arctic) has been studied for pollen, spores and aquatic palynomorphs, including freshwater green algae and cysts of marine dinoflagellates. The age model was established on the basis of radiocarbon dates obtained on marine bivalve mollusk shells. The available dates suggest that the analyzed sediment was accumulated during the last ca. 10.8 cal. ka and reveal two intervals with markedly different sedimentation rates, reflecting the sedimentary regime changes of the Laptev Sea shelf during postglacial sea-level rise. Very high sedimentation rates (ca. 4.7 mm per year) in the lower part of the core (120–866 cm) between ca. 9.2 and 10.8 cal. ka BP reflect lower-than-present sea levels, high erosion activity and much closer position of the palaeo-shoreline with the Lena and Yana river mouths to the core site. Dramatic decrease in sedimentation rates (ca. 0.1 mm per year) during the middle and late Holocene interval reflects high sea-level and decreased amount of suspended material transported to the outer shelf by rivers. Despite the location of the core site at the continental slope and far away from the modern coastline pollen, spores and fresh-water algae constitute a major part of the microfossils throughout the whole record, indicating great impact of the Lena and Yana rivers and possibly prevalent wind regime on the pollen and non-pollen-palynomorph (NPP) assemblages. Although a number of short-term (decadal to multi-century) oscillations deviate from the mean Holocene values, pollen taxa percentages and pollen-based numerical biome reconstructions do not show very clear trends. The latter is likely a result of the mixed environmental signal and complex pollen contribution of several large environmental regions and vegetation zones of Siberia drained by the Lena and Yana rivers. The greater pollen contribution of the forested regions to the PS51/118-3 record reflects higher pollen production of the boreal trees and shrubs over the low-productive Arctic vegetation. The intervals of the relative increase in the tundra biome scores in the PS51/118-3 record reflect decreased arboreal pollen production or/and increased landscape openness within the pollen source area and can be correlated (within the uncertainty of the age models) with the cold episodes observed in the Greenland ice and North Atlantic sediment records.

A continuous multi-millennial record of surficial bivalve mollusk shells from the São Paulo Bight, Brazilian shelf

To evaluate the potential of using surficial shell accumulations for paleoenvironmental studies, an extensive time series of individually dated specimens of the marine infaunal bivalve mollusk Semele casali was assembled using amino acid racemization (AAR) ratios (n=270) calibrated against radiocarbon ages (n=32). The shells were collected from surface sediments at multiple sites across a sediment-starved shelf in the shallow sub-tropical São Paulo Bight (São Paulo State, Brazil). The resulting 14C-calibrated AAR time series, one of the largest AAR datasets compiled to date, ranges from modern to 10,307calyr BP, is right skewed, and represents a remarkably complete time series: the completeness of the Holocene record is 66% at 250-yr binning resolution and 81% at 500-yr binning resolution. Extensive time-averaging is observed for all sites across the sampled bathymetric range indicating long water depth-invariant survival of carbonate shells at the sediment surface with low net sedimentation rates. Benthic organisms collected from active depositional surfaces can provide multi-millennial time series of biomineral records and serve as a source of geochemical proxy data for reconstructing environmental and climatic trends throughout the Holocene at centennial resolution. Surface sediments can contain time-rich shell accumulations that record the entire Holocene, not just the present.

Stratigraphy and wiggle-matching-based age-depth model of late Holocene marine sediments in Beppu Bay, southwest Japan

We analyzed the lithology, magnetic susceptibility, bulk density, and X-ray radiographs of 14 sediment cores (1–9m long) from Beppu Bay in the western Seto Inland Sea, Japan, to establish the late Holocene stratigraphy in the deepest part of the bay and to develop an age–depth model for the sediments there. The cores contained 18 thick (major event) high-density layers (16 turbidites and two volcanic ash; >1cm thick), and both lithological observations and density variations in the hemipelagic mud that is dominant in the cores revealed a further 55 thin (minor event) high-density layers (<1cm thick). Analyses of color properties and opal and sand contents of the hemipelagic mud defined nine lithological units. After stratigraphic correlation of the event layers among cores, we projected 14C dates onto a single composite core. Forty-two AMS 14C dates from bivalve mollusk shells were used to construct a wiggle-matching-based age–depth model for the late Holocene sequence and to determine the local reservoir effect (ΔR). The age–depth model showed a sedimentation rate of 0.23–0.30cm/yr for a 7.8m-long composite core and an age of ∼2800calyr BP at the base. Wiggle-matching provided ΔR values of 115–155yr for late Holocene bivalve samples from Beppu Bay, which is consistent with previous estimates reported from coastal areas near the Kuroshio Front. Comparison of wiggle-matching-derived ages of thick turbidites with the ages of historical earthquakes showed differences within ±25yr. Our study demonstrated that wiggle matching with optimal fitting based on either the weighted least-squares or maximum likelihood method can minimize the effect of scatter of age data due to reworking and burrowing of bivalves and thus improve the accuracy of age–depth models.

AN IMPROVED UNDERSTANDING OF THE ALASKA COASTAL CURRENT: THE APPLICATION OF A BIVALVE GROWTH-TEMPERATURE MODEL TO RECONSTRUCT FRESHWATER-INFLUENCED PALEOENVIRONMENTS

Shells of intertidal bivalve mollusks contain sub-seasonally to interannually resolved records of temperature and salinity variations in coastal settings. Such data are essential to understand changing land-sea interactions through time, specifically atmospheric (precipitation rate, glacial meltwater, river discharge) and oceanographic circulation patterns; however, independent temperature and salinity proxies are currently not available. We established a model for reconstructing daily water temperatures with an average standard error of ∼1.3 °C based on variations in the width of lunar daily growth increments of Saxidomus gigantea from southwestern Alaska, United States. Temperature explains 70% of the variability in shell growth. When used in conjunction with stable oxygen isotope data, this approach can also be used to identify changes in past seawater salinity. This study provides a better understanding of the hydrological changes related to the Alaska Coastal Current (ACC). In combination with δ18Oshell values, increment-derived temperatures were used to estimate salinity changes with an average error of 1.4 ± 1.1 PSU. Our model was calibrated and tested with modern shells and then applied to archaeological specimens. As derived from the model, the time interval of 988–1447 cal yr BP was characterized by ∼1–2 °C colder and much drier (2–5 PSU) summers. During that time, the ACC was likely flowing much more slowly than at present. In contrast, between 599–1014 cal yr BP, the Aleutian low may have been stronger, which resulted in a 3 °C temperature decrease during summers and 1–2 PSU fresher conditions than today; the ACC was probably flowing more quickly at that time. The shell growth–temperature model can be used to estimate seasonal to interannual salinity and temperature changes in freshwater-influenced environments through time.

Tafonomia de biválvios em calcários oolíticos da formação Teresina (Bacia do Paraná, Permiano Médio, Prudentópolis, PR)

Herein, it is presented the first detailed taphonomic study on bivalve mollusk shells preserved in the oolitic limestones of the Teresina Formation (probably Kungurian-Roadian, Lower-Middle Permian) in the eastern margin of the Parana basin. The selected beds are located in two quarries (informally named PRU 1 and PRU 2) in Prudentopolis municipality (Center-South Parana State), and positioned approximately in the middle of the formation and probably in the Pinzonella illusa Zone. The PRU 1 limestone (~30 cm thick), which is partially silicified and intercalated with predominantly pelitic rocks, is classified as a bivalve oolitic grainstone. The basal contact is erosive and the top shows symmetrical ripple marks, which are draped by shale with mud cracks. There are two fining-upwards successions characterized by dense to dispersed packing of the shells, which are usually disarticulated, randomly oriented (many nested/stacked) and mixed with some pelitic intraclasts. Microhummocky cross-stratification occurs a little below the top of the bed. The PRU2 bed is classified as ooid-bivalve rudstone (~5 cm thick), where all shells are disarticulated and fragmented, showing dense packing. The bivalves probably inhabited a muddy substrate and were mixed (as parautochtonous and allochthonous bioclasts) with ooids during high-energy storm events, including posterior shell displacement as a result of bioturbation. Thus, the calcareous beds represent amalgamated proximal tempestites with a complex taphonomic history, strong temporal/spatial mixing of bioclasts and limited paleoecological resolution. They are a typical example of shell beds generated in a huge epeiric sea, which was not necessarily connected to the ocean and where very low depositional-slope gradient, very slow subsidence and minimum sediment accommodation space caused frequent sediment reworking by storm related processes.

Nacre in Mollusk Shells as a Multilayered Structure with Strain Gradient

AbstractHow do living organisms attain the complicated shapes of grown bio‐composites? This question is answered when studying the mechanics of the nacre layer in the bivalve mollusk shells. In this study, the internal strains/stresses across the shell thickness are profiled as a function of depth by strain gauge measurements during controlled etching in the selected areas. Measurements of stress release under etching provide clear evidence that the investigated shells, in fact, are strained multilayered structures, which are elastically bent due to the forces evolving at the organic/inorganic interfaces. The stresses are mostly concentrated in the “fresh” nacre sub‐layers near the inner surface of the shell adjacent to the mollusk mantle. This analysis unexpectedly shows that the elastic bending of the nacre layer is due to strain gradients which are originated in the gradual in‐depth changes of the thickness of ceramic lamellae. The changes mentioned were directly observed by scanning electron microscopy. By this sophisticated design of the ultra‐structure of the nacre layer, the bowed shape of the bivalve shells is apparently achieved.

MoGroFunGen: A numerical model for reconstructing intra-annual growth rates of bivalve molluscs

Bivalve mollusc shells contain valuable archives of biological and environmental information. For example, periodic microgrowth increments record intra-annual growth rates that vary, in large part, as a function of temperature. Unfortunately, these increments are often not preserved, or were deposited at equivocal intervals, especially in fossils or shells with obscure increments. Here we present a new numerical model that reconstructs intra-annual growth rates by relating linear growth and time using oxygen isotopes from shell carbonate. The model involves converting observed oxygen isotope values from shell carbonate ( δ 18O carb) to temperatures, which requires knowledge of the oxygen isotope composition of water ( δ 18O water). Then calculated temperatures are converted to dates using temporally calibrated temperature records. Next, dates are plotted versus sample distance (measured from sampled shells), fit with a monotonic cubic spline, and finally the first derivative of this function is evaluated yielding the growth function. The variance of this function is estimated through resampling by incorporating the uncertainty associated with δ 18O measurement (e.g., ± 0.08‰). This numerical model produces a distribution of growth functions, from which we calculate the average growth function. Modeled growth functions agree well with independently derived growth functions, which suggests our modeling procedure produces reliable estimates of intra-annual growth rates. These data can, in turn, provide valuable ecological information, such as the timing of highest intra-annual growth rates, growth-limiting temperatures, and optimal growth temperatures. This final parameter is particularly important because optimal growth temperatures can now be estimated without any a priori knowledge of growth rates.

The use of raw and acid-pretreated bivalve mollusk shells to remove metals from aqueous solutions

Heavy metal removal from industrial wastewater is not only to protect living organisms in the environment but also to conserve resources such as metals and water by enabling their reuse. To overcome the disadvantage of high cost and secondary pollution by the conventional physico-chemical treatment techniques, environmentally benign and low-cost adsorbents are in demand. In this study, the use of raw and acid-pretreated bivalve mollusk shells (BMSs) to remove metals from aqueous solutions with single or mixed metal was evaluated at different BMSs doses, pH and temperatures in batch shaking experiments in laboratory conditions. When the BMSs were used to treat CuSO 4·5H 2O solution, the copper sorption capacities of the raw and acid-pretreated BMSs were approximately 38.93 mg/g and 138.95 mg/g, respectively. The copper removal efficiency (CRE) of the raw BMSs became greatly enhanced with increasing initial pH, reaching 99.51% at the initial pH 5. Conversely, the CRE of the acid-pretreated BMSs was maintained at 99.48–99.52% throughout the pH range of 1–5. Furthermore, the CRE values of the raw and acid-pretreated BMSs were not greatly changed when the temperature was varied from 15 °C to 40 °C. In addition, the CRE value of the raw BMSs was maintained for 12 cycles of sorption–desorption with a CRE of 98.4% being observed in the final cycle. Finally, when the BMSs were used to treat electroplating wastewater, the removal efficiencies (REs) of the raw BMSs were 99.97%, 98.99% and 87% for Fe, Zn and Cu, respectively, whereas the REs of the acid-pretreated BMSs were 99.98%, 99.43% and 92.13%, respectively. Ion exchange experiments revealed that one of mechanisms for metal sorption by the BMSs from aqueous solution is related to ion exchange, especially between the metal ions in the treated solution and Ca 2+ from BMSs. Infrared absorbance spectra analysis indicated that the acid pretreatment led to occurrence of the groups (i.e. –OH, –NH, C O and S O) of negative charge in treated BMSs. Scanning electron microscopy revealed that acid pretreatment enabled the used BMSs to form the flake-shaped structure with smooth surfaces that can supply a better interface for binding metal ions.

Biotic Interaction between Spionid Polychaetes and Bouchardiid Brachiopods: Paleoecological, Taphonomic and Evolutionary Implications

Shells of Bouchardia rosea (Brachiopoda, Rhynchonelliformea) are abundant in Late Holocene death assemblages of the Ubatuba Bight, Brazil, SW Atlantic. This genus is also known from multiple localities in the Cenozoic fossil record of South America. A total of 1211 valves of B. rosea, 2086 shells of sympatric bivalve mollusks (14 nearshore localities ranging in depth from 0 to 30 m), 80 shells of Bouchardia zitteli, San Julian Formation, Paleogene, Argentina, and 135 shells of Bouchardia transplatina, Camacho Formation, Neogene, Uruguay were examined for bioerosion traces. All examined bouchardiid shells represent shallow-water, subtropical marine settings. Out of 1211 brachiopod shells of B. rosea, 1201 represent dead individuals. A total of 149 dead specimens displayed polychaete traces (Caulostrepsis). Live polychaetes were found inside Caulostrepsis borings in 10 life-collected brachiopods, indicating a syn-vivo interaction (Caulostrepsis traces in dead shells of B. rosea were always empty). The long ...

ENSO-coupled precipitation records (1959–2004) based on shells of freshwater bivalve mollusks (Margaritifera falcata) from British Columbia

We present the results of sclerochronologi- cally calibrated growth and stable isotope analyses of the freshwater bivalve Margaritifera falcata collected from an agricultural, suburban setting near Vancouver, BC. The oxygen isotope range of shell aragonite can be explained by the temperature range during the growing season, assuming the water d 18 O composition remained constant. However, shell growth is strongly influenced by local summer precipitation and potentially runoff of nutrient-rich stormwater. About 44% of the variability of annual shell growth can be explained by amounts of local summer (June-September) rainfall. Local winter precipitation and El Nino-Southern Oscillation (ENSO) strength during the preceding year exert a weak, but significant control on shell growth. In com- bination, summer and winter precipitation can explain up to 50% of the variability in annual shell growth. Spectral analyses substantiate the effect of precipita- tion on shell growth and demonstrate that shell growth and ENSO are coupled by precipitation. Common spectral density was found at periods of 6.5-9 years, particularly between 1985 and 2004. Higher frequency oscillation corresponding to periods of 3-5 years occurred during the early 1970s, early to mid 1980s, and later 1990s. These results suggest that skeletal records of bivalve mollusks provide suitable archives of ENSO-coupled precipitation in areas where other climate proxies such as tree-rings and speleothems may not be available.

Scandinavian climate since the late 18th century reconstructed from shells of bivalve mollusks

Scandinavian climate since the late 18th century reconstructed from shells of bivalve mollusks

Taphonomic trade-offs in tropical marine death assemblages: Differential time averaging, shell loss, and probable bias in siliciclastic vs. carbonate facies

Radiocarbon-calibrated amino-acid racemization ages of individually dated bivalve mollusk shells from Caribbean reef, nonreefal carbonate, and siliciclastic sediments in Panama indicate that siliciclastic sands and muds contain significantly older shells (median 375 yr, range up to ;5400 yr) than nearby carbonate seafloors (median 72 yr, range up to ;2900 yr; maximum shell ages differ significantly at p , 0.02 using extreme-value statistics). The implied difference in shell loss rates is contrary to physicochemical expectations but is consistent with observed differences in shell condition (greater bioerosion and dissolution in carbonates). Higher rates of shell loss in carbonate sediments should lead to greater compositional bias in surviving skeletal material, resulting in taphonomic trade-offs: less time averaging but probably higher taxonomic bias in pure carbonate sediments, and lower bias but greater time averaging in siliciclastic sediments from humid-weathered accretionary arc terrains, which are a widespread setting of tropical sedimentation.