Astarte Borealis Research Articles

Seasonal SIMS δ18O record in Astarte borealis from the Baltic Sea tracks a modern regime shift in the NAO

IntroductionAstarte borealis holds great potential as an archive of seasonal paleoclimate, especially due to its long lifespan (several decades to more than a century) and ubiquitous distribution across high northern latitudes. Furthermore, recent work demonstrates that the isotope geochemistry of the aragonite shell is a faithful proxy of environmental conditions. However, the exceedingly slow growth rates of A. borealis in some locations (<0.2mm/year) make it difficult to achieve seasonal resolution using standard micromilling techniques for conventional stable isotope analysis. Moreover, oxygen isotope (δ18O) records from species inhabiting brackish environments are notoriously difficult to use as paleoclimate archives because of the simultaneous variation in temperature and δ18Owater values.MethodsHere we use secondary ion mass spectrometry (SIMS) to microsample an A. borealis specimen from the southern Baltic Sea, yielding 451 SIMS δ18Oshell values at sub-monthly resolution.ResultsSIMS δ18Oshell values exhibit a quasi-sinusoidal pattern with 24 local maxima and minima coinciding with 24 annual growth increments between March 1977 and the month before specimen collection in May 2001.DiscussionAge-modeled SIMS δ18Oshell values correlate significantly with both in situ temperature measured from shipborne CTD casts (r2 = 0.52, p<0.001) and sea surface temperature from the ORAS5-SST global reanalysis product for the Baltic Sea region (r2 = 0.42, p<0.001). We observe the strongest correlation between SIMS δ18Oshell values and salinity when both datasets are run through a 36-month LOWESS function (r2 = 0.71, p < 0.001). Similarly, we find that LOWESS-smoothed SIMS δ18Oshell values exhibit a moderate correlation with the LOWESS-smoothed North Atlantic Oscillation (NAO) Index (r2 = 0.46, p<0.001). Change point analysis supports that SIMS δ18Oshell values capture a well-documented regime shift in the NAO circa 1989. We hypothesize that the correlation between the SIMS δ18Oshell time series and the NAO is enhanced by the latter’s influence on the regional covariance of water temperature and δ18Owater values on interannual and longer timescales in the Baltic Sea. These results showcase the potential for SIMS δ18Oshell values in A. borealis shells to provide robust paleoclimate information regarding hydroclimate variability from seasonal to decadal timescales.

Sclerochronological records of environmental variability and bivalve growth in the Pacific Arctic

The Pacific Arctic region has experienced, and is projected to continue experiencing, rapid climate change. Large uncertainties exist in our understanding of the impact these physical changes have on the region’s ecology. This is, in part, due to the lack of long-term data. Here we investigate bivalve mollusc growth increment width chronologies (sclerochronologies) to develop a long-term biological data series in an Arctic species and address the hypothesis that benthic production in the Pacific Arctic region is in decline with implications for predators (e.g., walrus, whales, seals, and sea ducks). Growth increments formed in the shells of two bivalve mollusc species, Astarte borealis and Liocyma fluctuosa, were examined using conventional sclerochronological techniques. The A. borealis and L. fluctuosa samples exhibited measured longevities of >148 and >18 years, respectively, in the coastal waters of Alaska’s Chukchi Sea. Dendrochronology crossdating techniques facilitated the development of two robust (expressed population signal > 0.85) independent growth increment width chronologies. These chronologies provide evidence of the growth conditions through time for each species (1985–2015 for A. borealis and 1997–2014 for L. fluctuosa). Linear regression analyses identified that both species grew more rapidly in years with warmer sea surface temperature and lower sea ice concentration. The results provide evidence that benthic ecosystems are benefiting from the warmer conditions and reduced sea ice that have accompanied recent Arctic climate trends. This result is encouraging for benthic predators in the eastern Chukchi Sea as it alleviates the concern that their benthic prey has already become food limited by weakened pelagic-benthic coupling. More broadly, this initial A. borealis chronology is among the longest biological data series for any Arctic species and highlights the feasibility of multicentennial biological data for the Arctic.

High-Resolution Reconstruction of Dissolved Oxygen Levels in the Baltic Sea With Bivalves – a Multi-Species Comparison (Arctica islandica, Astarte borealis, Astarte elliptica)

An increasing area of shallow-marine benthic habitats, specifically in the Baltic Sea, is affected by seasonal oxygen depletion. To place the current spread of oxygen deficiency into context and quantify the contribution of anthropogenic ecosystem perturbation to this development, high-resolution archives for the pre-instrumental era are needed. As recently demonstrated, shells of the bivalve mollusk, Arctica islandica fulfil this task with molar Mn/Cashell ratios as proxies for dissolved oxygen (DO) levels in the water column. Since the ocean quahog is inhomogeneously distributed in the Baltic Sea and may not be present in museum collections or found throughout sedimentary sequences, the present study evaluated whether two other common bivalves, Astarte elliptica and Astarte borealis can be used interchangeably or alternatively as proxy DO recorders. Once mathematically resampled and corrected for shell growth rate-related kinetic effects and (some) vital effects, Mn/Cashell data of all three species (age ten onward in A. islandica) were statistically significantly (p < 0.0001) linearly and inversely correlated to DO concentration in the free water column above seafloor (r = –0.66 to –0.75, corresponding to 43 to 56% explained variability). A. elliptica may provide slightly more precise DO data (1σ error of ±1.5 mL/L) than A. islandica or A. borealis ( ± 1.6 mL/L), but has a shorter lifespan. Both Astarte species show a stronger correlation with DO than A. islandica, because their biomineralization seems to be less severely hampered by oxygen and salinity stress. In turn, A. islandica grows faster resulting in less time-averaged data. During youth, the ocean quahog typically incorporates a disproportionately large amount of manganese into its shell, possibly because food intake occurs directly at the sediment-water interface where Mn-rich porewater diffuses out of the sediment. With increasing age, however, A. islandica seems to generate a gradually stronger inhaling water current and takes in a larger proportion of water farther away from the fluffy layer. As demonstrated here, all three studied species can be used as DO archives, though species-specific limitations should be kept in mind.

Age and growth of Astarte borealis (Bivalvia) from the southwestern Baltic Sea using secondary ion mass spectrometry

Traditional isotope sclerochronology employing isotope ratio mass spectrometry has been used for decades to determine the periodicity of growth increment formation in marine organisms with accretionary growth. Despite its well-demonstrated capabilities, it is not without limitation. The most significant of these being the volume of carbonate powder required for analysis with conventional drill-sampling techniques, which limit sampling to early in ontogeny when growth is fast or to species that reach relatively large sizes. In species like Astarte borealis (Schumacher, 1817), a common component of Arctic boreal seas, traditional methods of increment analysis are difficult, because the species is typically long-lived, slow growing, and forms extremely narrowly spaced growth increments. Here, we use Secondary Ion Mass Spectrometry (SIMS) to analyze δ18O in 10-μm-diameter spots and resolve the seasonal timing of growth increment formation in Astarte borealis in the southeastern Baltic Sea. In the individaul sampled here, dark growth increments can form in either the fall, winter, or spring. Furthermore, growth increment data from two populations (RFP3S = 54.7967° N, 12.38787° E; WA = 54.86775° N, 14.09832° E) indicate that in the Baltic Sea, A. borealis is moderately long-lived (at least 43 years) and slow growing (von Bertalanffy k values 0.08 and 0.06). Our results demonstrate the potential of A. borealis to be a recorder of Baltic Sea seasonality over the past century using both live- and dead-collected shells, and also the ability of SIMS analysis to broaden the spectrum of bivalves used in sclerocrhonological work.

Lipid markers and compound-specific carbon isotopes as diet and biosynthesis reflectors in the northern Neptune whelk Neptunea heros

A suite of lipid biomarkers plus compound-specific carbon isotopes of major sterols were determined in muscle tissues across increasing sizes of northern Neptune whelks Neptunea heros, developing eggs and potential diets to link trophic patterns, metabolism and carbon sources on the Chukchi Sea shelf. Analysis of primary prey included the northern clam Astarte borealis, water column particulate organic matter (POM) and surface sediments near the collection sites. Sterols specific to major algal groups along with algal-derived polyunsaturated fatty acids (C20:5n-3, C20:4n-3, C22:6n-3) in whelk muscle tissue reflected the importance of algal primary production to benthic consumers and its direct incorporation. Compound-specific carbon isotope values of cholesterol and Δ5,7-sterols present in foot muscle of N. heros also suggest a transition from scavenging/detrital feeding in smaller juveniles to predatory consumption by larger adults. Sexually mature adult female N. heros (shell lengths >10 cm) contained lower sterol concentrations compared to smaller whelks, which may reflect reduced consumption rates or lipid translocation during the annual reproductive cycle. Analysis of N. heros eggs at 3 developmental stages ranging from internal egg masses to mature egg cases showed significant transfer of algal-derived sterols and fatty acids which were conserved during egg maturation. The suite of individual lipid signatures and δ13C sterol values observed in N. heros suggest that the northern Neptune whelk relies on both direct lipid incorporation as well as metabolic modification of algal-derived food sources for sterol requirements that transition as animals mature and become predatory consumers.

Age and growth of Astarte borealis (Bivalvia) from the southwestern Baltic Sea using secondary ion mass spectrometry

Age and growth of Astarte borealis (Bivalvia) from the southwestern Baltic Sea using secondary ion mass spectrometry

Integrated study of benthic foraging resources for Atlantic walrus (Odobenus rosmarus rosmarus) in the Pechora Sea, south‐eastern Barents Sea

Abstract The Atlantic walrus, Odobenus rosmarus rosmarus, forms a herd of nearly 4,000 heads in the Pechora Sea (south‐eastern Barents Sea). The Near Threatened status of O. rosmarus rosmarus and the relative isolation of the Pechora Sea population, as well as the potential impacts of human activities in the area, make it important to characterize key habitats, including feeding grounds, in order to protect the species. The aim of the present study was to integrate multiple sources of environmental and biological data collected by satellite telemetry, remotely operated vehicle (ROV), and benthic grab sampling to examine the distribution and diversity of benthic foraging resources used by walrus in the Pechora Sea. Analysis of satellite telemetry data from seven males tagged on Vaigach Island helped to identify areas of high use by walruses near haulout sites on Matveev and Vaigach islands, and in between. Field data were collected from those feeding grounds in July 2016 using ROV video recordings and bottom grab sampling. Analysis of 19 grab stations revealed a heterogeneous macrobenthic community of 133 taxa with a mean biomass of 147.11 ± 7.35 g/m2. Bivalve molluscs, particularly Astarte borealis, Astarte montagui, and Ciliatocardium ciliatum, dominated the overall macrobenthic biomass, making up two‐thirds of the total. Analysis of 16 ROV video transects showed high occurrences of mobile benthic decapods (3.03 ± 2.74 ind./min) and provided the first direct evidence that areas actively used by walrus in the Pechora Sea overlap with the distribution of the non‐native omnivorous snow crab, Chionoecetes opilio. Integrating multiple data sources provides an early foundation for the kinds of ecosystem‐based approaches needed to improve Pechora Sea resource management and to underpin Russia’s nascent marine spatial planning initiatives. Factors that need to be considered in marine spatial planning include impacts on benthic feeding grounds from offshore oil and gas development and the spread of the snow crab.

Spatial structure of the macroand meiobenthic communities in homogenous conditions (on the example of the Pechora Sea)

Spatial structure of the macroand meiobenthic communities of the south-eastern Barents Sea (also known as Pechora Sea) was investigated in 2003 during the expedition of the RV «Professor Shtokman». One grid of the stations was used for both benthic size classes. Community dominated by Serripes groenlandicus occupied the most part of the investigated polygon, Astarte borealis dominated the easternmost station. Described communities are in correspondence with historic data. In the meiobenthic communities, nematodes played a leading role, accounting for 86–94% of the total number. Nematode Richtersia inaequalis was dominant on most stations, at the northernmost station the nematodes Cervonema papillatum and Microlaimus affinis dominated. The temperature and the salinity of the near-bottom water layer were homogenous, macroand meiobenthic communities were not influenced by grain size. In contrast to our expectations, communities of the macroand meiobenthos were distributed independently of each other on the mesoscale area (30×11 km).

Spatial Structure of Macro- and Meiobenthic Communities in a Homogeneous Environment (on the Example of the Pechora Sea)

A study was performed in 2003 during the cruise of the R/V Professor Shtokman. A single sampling grid and similar approaches to community identification and analysis were used for both size classes of the benthos. A macrobenthic community dominated by Serripes groenlandicus occupied the majority of the study area, whereas Astarte borealis dominated at the easternmost station. Nematodes played a leading role in the meiobenthic communities, where they accounted for 86–94% of the total abundance. The nematode Richtersia inaequalis dominated in almost all areas, while Cervonema papillatum and Microlaimus affinis dominated in the northernmost part of the study area. Temperature, salinity, and grain-size characteristics did not affect the distribution of macro- and meiobenthic communities. The distribution of mosaic elements of macrobenthos and meiobenthos was independent of each other in a mesoscale (30 km long and 11 km wide) study area.

Biomarker responses and biotransformation capacity in Arctic and temperate benthic species exposed to polycyclic aromatic hydrocarbons

Monitoring parameters for the assessment of oil and gas related contaminants and their biological effects need validation before application in the Arctic. For such monitoring purposes, we evaluated the potential use of three biomarkers (acetylcholinesterase, acyl-CoA oxidase and glutathione S-transferase) for application to an Arctic bivalve (Astarte borealis) and determined the body residue of pyrene and two pyrene metabolites (1-hydroxypyrene and pyrene-1-glucuronide) in Arctic benthic species (bivalve: Macoma calcarea; polychaete: Nephtys ciliata) and temperate benthic species (bivalve: Limecola balthica; polychaete: Alitta virens) in order to establish the potential of polycyclic aromatic hydrocarbons (PAHs) metabolite profiles as biomarkers of exposure in such species. Experimental PAH exposure levels were probably too low (0.2–1.7 mg/kg dry weight in sediment) to induce or inhibit biomarker responses in A. borealis. Concentrations of pyrene and pyrene metabolites varied between species, although no consistent patterns could be established among taxonomic groups and locations. Metabolites made up to 79% of the total pyrene concentrations, indicating that basal metabolic activity is affecting pyrene kinetics even at low concentrations in all species. This indicates that Arctic and temperate species could show similar metabolism patterns of PAHs, although more insight into the effects of confounding factors is needed.

Lifespan and growth of Astarte borealis (Bivalvia) from Kandalaksha Gulf, White Sea, Russia

Marine bivalves are well known for their impressive lifespans. Like trees, bivalves grow by accretion and record age and size throughout ontogeny in their shell. Bivalves, however, can form growth increments at several different periodicities depending on their local environment. Thus, establishing lifespans and growth rates of marine bivalves requires a proper identification of annual growth increments. Here, we use isotope sclerochronology to decipher the accretionary growth record of modern Astarte borealis from the White Sea, Russia (N 67°05.70′; E 32°40.85′). Unlike winter growth increments observed in many other cold-temperate and boreal bivalve and limpet species, prominent growth increments in A. borealis corresponded to the most negative values in the oxygen isotope (δ18O) time series indicating that they formed during summer. Furthermore, summer growth increments do not coincide with the external concentric ridges on the shell making the latter feature an unreliable indicator of age. Similar to many other polar bivalves, A. borealis shows slow growth and long life. The von Bertalanffy growth equation for our sample is Ht = 29.39*(1 − e(− 0.11(t−(− 1.86))). Lifespans of individuals examined here (n = 18) range from 16 to 48 years. Given its impressive longevity and widespread polar distribution, A. borealis may be a potentially valuable skeletal archive for monitoring environmental conditions in the Arctic Ocean and boreal seas in the face of changing climate.

Ecology of the bottom fauna and bioaccumulation of trace metals along the Lena River–Laptev Sea transect

The first data on ecology and trace metal (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb) bioaccumulation by macrozoobenthic organisms in area along the 130°E meridional transect from shallow water near the Lena River’s delta till the 78°N are presented. At the newly discovered methane seeps in the shallow Laptev Sea areas (72 m depth), a higher total abundance and biomass compared with background stations were recorded. In carbonate shells and soft tissues of Bivalvia Portlandia arctica and Astarte borealis, the high concentrations of Mn, Fe, Pb, Ni and Co were detected that varied in dependence from sampling site. In the dominating taxa of brittle stars (Ophiuroidea), there were found no significant differences between majority of trace metal content in organisms inhabiting the seeps area and background ones. An elevated content of some metals was detected in the Asteroidea bodies that may be attributed to its trophic behavior (deposit feeder).

Lifespan and growth of Astarte borealis (Bivalvia) from Kandalaksha Gulf, White Sea, Russia

Lifespan and growth of Astarte borealis (Bivalvia) from Kandalaksha Gulf, White Sea, Russia

Implications of ocean acidification in the Pacific Arctic: Experimental responses of three Arctic bivalves to decreased pH and food availability

Recent sea ice retreat and seawater warming in the Pacific Arctic are physical changes that are impacting arctic biological communities. Recently, ocean acidification from increases in anthropogenic CO2 has been identified as an additional stressor, particularly to calcifying organisms like bivalves. These bivalves are common prey items for benthivorous predators such as Pacific walruses (Odobenus rosmarus divergens), bearded seals (Erignathus barbatus), and diving seaducks, such as Spectacled Eiders (Somateria fischeri). We investigated the effects of decreased pH and food availability on growth (% change in length and wet weight and allometric growth characterizations) and oxygen consumption (mg/L/hour) of three common Arctic bivalves, Macoma calcarea, Astarte montagui, and Astarte borealis. Two sets of experiments were run for seven and eleven weeks, exposing the bivalves to control (8.05 ± 0.02 and 8.19 ± 0.003, respectively) and acidified (7.76 ± 0.01 and 7.86 ± 0.01, respectively) pH treatments. Length, weight, and oxygen consumption were not significantly different among the varying treatments after the seven-week exposure and only one significant effect of decreased pH and one significant effect of decreased food availability were observed after the end of the eleven-week exposure. Specifically, shells of A. borealis displayed a decrease in length in response to decreased pH and M. calcarea showed a decrease in length in response to limited food. The negative effects of pH observed in the experiments on growth and oxygen consumption were small, suggesting that at least two of these species are generally resilient to decreasing pH.

Shell form, growth, and production of Astarte borealis (Schumacher, 1817) (Astartidae, Bivalvia) in the southeastern Baltic Sea

The relationships between the linear dimensions and body weight and the ratio between the masses, growth, and production were studied for the bivalve Astarte borealis inhabiting the southeastern Baltic Sea. The maximal shell length was 21.09 mm, while the maximum age was 8+. The linear growth was described by the Bertalanffy equation Lτ = 35.53(1 - e -0.0894(τ-(-0.7354)) ). The annual production was 7.60 kJ/m 2 at a Ps/B coefficient of 0.41. It was found that the A. borealis inhabiting the southeastern Baltic Sea was characterized by a lower linear growth rate compared to the mollusks of other parts of the geograph� ical range due to the low salinity of the Baltic Sea.

Diversity, distribution and ecology of benthic molluscan communities on the Portuguese continental shelf

The diversity, ecology and distribution patterns of the Portuguese continental shelf malacofauna and its relationship with abiotic factors were studied from samples covering the western and the southern coast. A total of 2544 specimens were identified corresponding to 169 taxa, mostly bivalves (62% of the total taxa). Abra alba was the most abundant and the most frequent species. The alpha diversity ranged from one species to 21 spp. 0.1m−2. The highest abundance and diversity were obtained in coarser sediments. Multivariate analysis based on the abundance data identified five major malacological groups: (a) Angulus pygmaeus and Thracia villosiuscula in the coarser sediments of the western inner and mid shelf; (b) Calyptraea chinensis and Leptochiton cancellatus in the heterogeneous and organically enriched sediments of the southern shelf; (c) Angulus fabula, Spisula subtruncata and Pharus legumen in the near shore exposed fine sands; (d) A. alba in muddy fine sands, mainly in the northwestern shelf and (e) Saccella commutata in the southwestern deeper shelf. The malacofauna could be used as a proxy for the major benthic communities known to occur in this area, except in muddy patches, where molluscs were absent or low abundant. Median grain-size, gravel content, depth and hydrodynamic regime were the environmental factors best related to the malacofauna spatial distribution patterns. This study sets the first record of Astarte borealis, Leptochiton asellus, Mercenaria mercenaria and Montacuta phascolionis in the Portuguese shelf and the most northern limit for Anadara polii, Glycymeris nummaria, and Leptochiton algesirensis along the northwestern shelf. This study also gives new ecological insights for several species, in terms of bathymetric range distribution, as well as habitat type and highlighted the transitional characteristics of the molluscan communities from this particular northeastern Atlantic area where boreal, temperate and subtropical faunas can coexist.

Mercury in the northeastern Chukchi Sea: Distribution patterns in seawater and sediments and biomagnification in the benthic food web

Mercury contamination in the atmosphere, snow and marine mammals of the Arctic has been a continuing environmental concern and the focus of many investigations. Much less is known about the distribution of Hg in seawater, sediments and organisms from lower trophic levels in the Arctic, especially the Chukchi Sea. The onset of sea-ice retreat, severe coastal erosion, enhanced primary productivity and offshore energy development in the northeastern Chukchi Sea (NECS) signal changes to a system for which we have limited data for potentially toxic chemicals. To help us better understand and explain any future changes, we present here a combined data set for Hg in seawater, sediments and the following organisms from the NECS: amphipods (Ampelisca macrocephala), clams (Astarte borealis), snow crabs (Chionoecetes opilio), arctic cod (Boreogadus saida) and whelks (Buccinum spp. and Neptunea heros). Concentrations of total dissolved Hg (THgd) averaged (±standard deviation) 2.8±1.4pM in the NECS, ~2 times greater than values of 1.5±0.5pM for the Bering Strait. Overall, consistently lower concentrations of THgd were found at depths with markedly higher concentrations of chlorophyll a. Concentrations of total Hg (THg) in sediments from the NECS averaged 31±10ngg−1, correlated well with silt+clay, Al and TOC, and showed a long-term record consistent with the natural, background environment. Very localized occurrences of sediment with elevated THg concentrations were identified near two exploratory drilling sites where drilling mud and formation cuttings were discharged in 1989. Concentrations of sediment monomethylmercury (MMHg) averaged 0.15±0.07ngg−1 and accounted for only 0.43±0.17% of the sediment THg. The lowest average value (± standard error) for THg in biota was found for A. borealis at 44±4ngg−1 dry weight (d. wt.) with 33% of the THg present as MMHg. The highest average values for THg were identified for the whelks N. heros (195±29ngg−1, d. wt) and Buccinum spp. (269±54ngg−1, d. wt) with 95% of the THg present as MMHg in N. heros, the highest trophic level organism in this study as determined using data for δ15N. Biomagnification of MMHg was observed in this benthic food web with the following relationship: log[MMHg]=0.19[δ15N]−0.84 (R2=0.80, p=0.02).

Benthic ecology of the northeastern Chukchi Sea. Part I. Environmental characteristics and macrofaunal community structure, 2008–2010

Spatial variations of processes driving macrofaunal distributions can arise from interactions among topographic features and oceanographic patterns, and are not understood at small scales in the northeastern Chukchi Sea. Benthic macrofauna and environmental characteristics were measured to determine factors driving macrofaunal distributions as part of a multidisciplinary environmental program in the northeastern Chukchi Sea from 2008 to 2010. Macrofauna were sampled in three study areas, named Klondike, Burger, and Statoil, with a van Veen grab at up to 82 stations each year, as well as an area where marine mammals were seen feeding. The macrofaunal assemblages in all study areas were similar in species-composition with deposit-feeding polychaetes (53% of density and of 26% biomass) and bivalves (15% of density and 52% of biomass) collectively the most prominent groups. Maldane sarsi dominated the polychaetes in terms of both density and biomass, while bivalves were numerically dominated by Ennucula tenuis, but their biomass was dominated by larger species such as Macoma calcarea and Astarte borealis. Exceptions occurred in the marine mammal feeding area that was dominated by amphipods (71% of density and 30% biomass). Average densities were higher in Burger than in Klondike or Statoil, while biomass values were similar between Burger and Statoil, and higher in these two study areas than in Klondike. Overall, the distributions, biomass and density of benthic macrofauna reflect the high volume of production reaching the seafloor in the shallow waters of the Chukchi Sea. Variations in community structure among study areas were correlated with water depth and bottom-water temperature. Short-term temporal differences in community structure covaried with interannual oceanographic variations that may have altered food availability, macrofaunal survival, or larval recruitment. Topographic control over circulation appears to be a primary driver in structuring benthic communities within the present study region, as well as throughout the Chukchi Sea.

Paving the way for the new generations: Astarte borealis population dynamics in the White Sea

Populations of marine bivalves are known to be unstable but it is unclear whether this instability has internal or external causes. In this paper we summarize results from long-term (1978–2007) monitoring of an Astarte borealis (Astartidae) population in the White Sea. We sought significant long-term changes among a population of subtidal clams existing under relatively stable conditions. The studied population was initially (in 1978–1995) formed exclusively by adult clams, with no recruitment occurring until a mass inflow of unidentified astartid’s juveniles in the late 1990s. We assessed the suitability of periostracum microsculpture for identification of astartid juveniles and identified the juveniles recruited the population as A. borealis. Thus significant changes in population structure were detected. Our study suggests that A. borealis may have a very long life span (>20 years) and a prolonged recruitment failure could be associated with scarcity of hard substrates needed for egg attachment in a silted environment. As old clams died, their valves provided a hard substrate on the bottom surface, facilitating recruitment. We propose a new conceptual model of subtidal clams’ population dynamics predicting long-term cyclic changes driven by internal mechanisms associated with an unusual type of positive influence of adults upon recruits.

Dating High Arctic Holocene relative sea level changes using juvenile articulated marine shells in raised beaches

High Arctic raised beaches provide evidence for changes in relative sea-level (RSL), sea-ice extent, storminess, and variations in sediment supply. In many High Arctic areas, driftwood and whale bone are usually the preferred targets for radiocarbon dating, with marine shells a third choice because of their often large age and height uncertainties with respect to former sea level. Here we detail a new approach to sampling marine shells that reduces these problems by targeting juvenile, articulated specimens of Astarte borealis that are washed onto the beach under storm conditions and become incorporated into the beach crest. Radiocarbon dates from articulated valves of A. borealis from eight raised beaches from Billefjorden, Svalbard, provide a chronology for Holocene beach ridge formation and RSL change that compares favourably to the most precise records developed from elsewhere in Svalbard using driftwood or whale bone. We demonstrate the value of this new approach by comparing our record with previously published RSL data from eastern Svalbard to test different models of Late Weichselian ice load in this region. We find support for a major ice dome centred south and east of Kong Karls Land but no evidence for a significant ice dome located over easternmost Spitsbergen or southern Hinlopen Strait as proposed from recent marine geophysical survey. The approach is potentially applicable elsewhere in Svalbard and the High Arctic to address questions of RSL change and beach ridge chronology, and hence wider questions regarding palaeoclimate and ice load history.