Bivalve Arctica Islandica Research Articles

Population dynamics of Arctica islandica off Long Island (USA): an analysis of sex-based demographics and regional comparisons

The boreal bivalve Arctica islandica is an important fishery in the United States (US), yet very little is known about the resiliency of this species to fishing activity due to limited understanding of localized population demographics. Demographics including age frequency, recruitment patterns, mortality rates, and sexual dimorphism were evaluated for a population sampled off Long Island (LI, 40.09658°N 73.01057°W) and compared with samples from Georges Bank (GB, 40.72767°N, 67.79850°W) collected in 2015 and 2017, where GB was described in a previous study. This study supports evidence that this species is sexually dimorphic. Earlier assumptions of prolonged lapses in recruitment were not substantiated for either the GB or LI populations; yearly cohorts were observed for the past century, and both populations presented recruitment pulses in approximately 8-y periods. Estimated ages from this study are older than previously reported for the US Mid-Atlantic with the oldest animal represented by a 310-year-old male collected from LI. Simulated total mortality was higher at GB than LI, and higher for GB females than GB males, with simulated mean longevity estimates greater at LI than GB. The population sex ratio at GB was 1:1.1 (female:male), whereas the LI ratio was 1:1.4 and relatively deficient in large females. Recruitment into the populations occurs routinely with substantial hiatuses being rare and substantive year classes occurring at least decadally with lesser, but contributing, recruitment in most years in between. Routine recruitment may insulate this species from risks posed by overfishing to an extent not typical for other long-lived species.

The longest-lived metazoan, Arctica islandica, exhibits high mitochondrial H2O2 removal capacities

A greater capacity of endogenous matrix antioxidants has recently been hypothesized to characterize mitochondria of long-lived species, curbing bursts of reactive oxygen species (ROS) generated in this organelle. Evidence for this has been obtained from studies comparing the long-lived naked mole rat to laboratory mice. We tested this hypothesis by comparing the longest-lived metazoan, the marine bivalve Arctica islandica (MLSP = 507 y), with shorter-lived and evolutionarily related species. We used a recently developed fluorescent technique to assess mantle and gill tissue mitochondria’s capacity to consume hydrogen peroxide (H2O2) in multiple physiological states ex vivo. Depending on the type of respiratory substrate provided, mitochondria of Arctica islandica could consume between 3 and 14 times more H2O2 than shorter-lived species. These findings support the contention that a greater capacity for the elimination of ROS characterizes long-lived species, a novel property of mitochondria thus far demonstrated in two key biogerontological models from distant evolutionary lineages.

Relationship between plankton dynamics and growth of the long-lived clam Arctica islandica on the Faroe shelf

Marine ecosystem dynamics can vary on timescales ranging from months to centuries, but many observational data are limited to just a few decades. The bivalve Arctica islandica may live up to five centuries depositing annual growth increments in its shells which can serve as an indicator for ecosystem productivity. In the present study, 154 specimens of A. islandica were collected on the Faroe Shelf and standardised annual growth increments for 143 of them – 44 from coastal stations and 99 from shelf stations – were compared with climatic, oceanographic and biological variables. A. islandica growth from coastal and shelf stations was not correlated with basin-scale climate indices (the AMO index, the NAO index, the AO index or the subpolar gyre index) or, more locally, with windspeed or sea surface temperature on the Faroe Shelf. For the shelf stations there was a significant negative correlation between A. islandica growth and the volume transport of the Faroe Current flowing just north of Faroe Islands (r = -0.62). There was a weak nonsignificant positive correlation with an index of primary production on the Faroe Shelf (r = 0.31) and a strong negative correlation with a zooplankton biomass index in mid-summer (r = -0.76). There was also a strong positive correlation between A. islandica growth and the biomass of the bottom-feeding fish species Melanogrammus aeglefinus two years later (r = 0.62). These results seem to suggest that A. islandica growth may represent the amount of fresh phytoplankton that reaches the near-bottom water layers and could probably be regarded as a proxy for the strength of pelagic-benthic coupling that is modulated through phytoplankton-zooplankton interactions in the overlying water. Our results highlight the potential for A. islandica to serve as a long-term proxy for linking variability in pelagic ecosystem dynamics to demersal fish stocks.

Experimental burial diagenesis of aragonitic biocarbonates: from organic matter loss to abiogenic calcite formation

Abstract. Carbonate biological hard tissues are valuable archives of environmental information. However, this information can be blurred or even completely lost as hard tissues undergo diagenetic alteration. This is more likely to occur in aragonitic skeletons because bioaragonite often transforms into calcite during diagenesis. For reliably using aragonitic skeletons as geochemical proxies, it is necessary to understand in depth the diagenetic alteration processes that they undergo. Several works have recently investigated the hydrothermal alteration of aragonitic hard tissues during short-term experiments at high temperatures (T > 160 ∘C). In this study, we conduct long-term (4 and 6 months) hydrothermal alteration experiments at 80 ∘C using burial-like fluids. We document and evaluate the changes undergone by the outer and inner layers of the shell of the bivalve Arctica islandica, the prismatic and nacreous layers of the hard tissue of the gastropod Haliotis ovina, and the skeleton of the coral Porites sp. combining a variety of analytical tools (X-ray diffraction, thermogravimetry analysis, laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and atomic force microscopy). We demonstrate that this approach is the most adequate to trace subtle, diagenetic-alteration-related changes in aragonitic biocarbonate structural hard materials. Furthermore, we unveil that the diagenetic alteration of aragonitic biological hard tissues is a complex multi-step process where major changes occur even at the low temperature used in this study, well before any aragonite into calcite transformation takes place. Alteration starts with biopolymer decomposition and concomitant generation of secondary porosity. These processes are followed by abiogenic aragonite precipitation that partially or totally obliterates the secondary porosity. Only subsequently does the transformation of the aragonite into calcite occur. The kinetics of the alteration process is highly dependent on primary microstructural features of the aragonitic biomineral. While the skeleton of Porites sp. remains virtually unaltered for the entire duration of the conducted experiments, Haliotis ovina nacre undergoes extensive abiogenic aragonite precipitation. The outer and inner shell layers of Arctica islandica are significantly affected by aragonite transformation into calcite. This transformation is extensive for the prismatic shell layer of Haliotis ovina. Our results suggest that the majority of aragonitic fossil archives are overprinted, even those free of clear diagenetic alteration signs. This finding may have major implications for the use of these archives as geochemical proxies.

Presence of male mitochondria in somatic tissues and their functional importance at the whole animal level in the marine bivalve Arctica islandica

Metazoans normally possess a single lineage of mitochondria inherited from the mother (♀-type mitochondria) while paternal mitochondria are absent or eliminated in fertilized eggs. In doubly uniparental inheritance (DUI), which is specific to the bivalve clade including the ocean quahog, Arctica islandica, ♂-type mitochondria are retained in male gonads and, in a few species, small proportions of ♂-type mitochondria co-exist with ♀-type in somatic tissues. To the best of our knowledge, we report, for the first time in metazoan, the natural occurrence of male and female individuals with exclusively ♂-type mitochondria in somatic tissues of the bivalve A. islandica. Mitochondrial genomes differ by ~5.5% at DNA sequence level. Exclusive presence of ♂-type mitochondria affects mitochondrial complexes partially encoded by mitochondrial genes and leads to a sharp drop in respiratory capacity. Through a combination of whole mitochondrial genome sequencing and molecular assays (gene presence and expression), we demonstrate that 1) 11% of individuals of an Icelandic population appear homoplasmic for ♂-type mitochondria in somatic tissues, 2) ♂-type mitochondrial genes are transcribed and 3) individuals with ♂-type mitochondria in somatic cells lose 30% of their wild-type respiratory capacity. This mitochondrial pattern in A. islandica is a special case of DUI, highlighted in individuals from both sexes with functional consequences at cellular and conceivably whole animal level.

Persistent Multidecadal Variability Since the 15th Century in the Southern Barents Sea Derived From Annually Resolved Shell‐Based Records

AbstractIn the North Atlantic Ocean, multidecadal variability in sea surface temperatures (SSTs) over the past several centuries has largely been inferred through terrestrial proxies and decadally resolved marine proxies. Annually resolved proxy records from marine archives provide valuable insight into this variability, but are especially rare from high latitude environments, particularly for centennial timescales. We constructed continuous, absolutely dated records of shell growth (1449–2014 CE; 564 years) and oxygen isotope ratios (δ18Oshell; 1539–2014 CE; 476 years) from shells of the bivalve Arctica islandica from coastal northern Norway, a location sensitive to large‐scale North Atlantic Ocean dynamics. An annual (January–December) SST reconstruction derived from δ18Oshell for the past five centuries suggests an increase of at least 2°C from the mid‐18th century to 2014. The SST reconstruction correlates significantly with instrumental records and with other proxy reconstructions in the southern Barents Sea region. Spectral analysis of the shell growth and isotope records supports evidence for Atlantic multidecadal variability (65–80 year periodicity) extending into polar and subpolar latitudes for the past five centuries. These results provide additional evidence that multidecadal variability in SSTs are a persistent feature of the North Atlantic marine system.

Nitric oxide mediates metabolic functions in the bivalve Arctica islandica under hypoxia.

The free radical nitric oxide (NO) is a powerful metabolic regulator in vertebrates and invertebrates. At cellular concentrations in the nanomolar range, and simultaneously reduced internal oxygen partial pressures (pO2), NO completely inhibits cytochrome-c-oxidase (CytOx) activity and hence mitochondrial- and whole-tissue respiration. The infaunal clam Arctica islandica regulates pO2 of hemolymph and mantle cavity water to mean values of <5 kPa, even in a completely oxygen-saturated environment of 21 kPa. These low internal pO2 values support a longer NO lifespan and NO accumulation in the body fluids and can thus trigger a depression of metabolic rate in the clams. Measurable amounts of NO formation were detected in hemocyte cells (~110 pmol NO 100−1 hemocytes h-1 at 6 kPa), which was not prevented in the presence of the NO synthase inhibitor L-NAME, and in the gill filaments of A. islandica. Adding a NO donor to intact gills and tissue homogenate significantly inhibited gill respiration and CytOx activity below 10 kPa. Meanwhile, the addition of the NO-oxidation product nitrite did not affect metabolic rates. The high nitrite levels found in the hemolymph of experimental mussels under anoxia do not indicate cellular NO production, but could be an indication of nitrate reduction by facultative anaerobic bacteria associated with tissue and/or hemolymph biofilms. Our results suggest that NO plays an important role in the initiation of metabolic depression during self-induced burrowing and shell closure of A. islandica. Furthermore, NO appears to reduce mitochondrial oxygen radical formation during surfacing and cellular reoxygenation after prolonged periods of hypoxia and anoxia.

Assessment of Ba/Ca in Arctica islandica shells as a proxy for phytoplankton dynamics in the Northwestern Atlantic Ocean

Despite its major role as a global climate regulator, little is known about the recent evolution of the North Atlantic Ocean, especially prior to the fifties, principally because of the lack of long-term instrumental data. Moreover, the North Atlantic Ocean is undergoing rapid changes at the physical scale leading to modifications at the biological scale increasing interest to monitor the environment. The phytoplankton is the base of the ocean life and its perturbation can lead to further changes in the food chain. Recording its dynamics implies to observe both its spatial and temporal variations. This study brings forward the use of the Ba/Ca ratio from shells of the long-living bivalve Arctica islandica collected in the Northwestern Atlantic Ocean near Saint-Pierre and Miquelon (SPM) as a recorder of the past and present phytoplankton dynamics. A high inter and intra-reproducibility and synchrony between Ba/Cashell profiles were demonstrated allowing the reconstruction of a 124 years annually-resolved Ba/Cashell master chronology (from 1893 to 2016). This master chronology was positively correlated to the surface chlorophyll a measured by satellite sensor at regional (around SPM) and global scales (Northwestern Atlantic).

Mitochondrial Traits Previously Associated With Species Maximum Lifespan Do Not Correlate With Longevity Across Populations of the Bivalve Arctica islandica.

The mitochondrial oxidative stress theory of aging posits that membrane susceptibility to peroxidation and the organization of the electron transport system (ETS) linked with reactive oxygen species (ROS) generation are two main drivers of lifespan. While a clear correlation has been established from species comparative studies, the significance of these characteristics as potential modulators of lifespan divergences among populations of individual species is still to be tested. The bivalve Arctica islandica, the longest-lived non-colonial animal with a record lifespan of 507 years, possesses a lower mitochondrial peroxidation index (PI) and reduced H2O2 efflux linked to complexes I and III activities than related species. Taking advantage of the wide variation in maximum reported longevities (MRL) among 6 European populations (36–507 years), we examined whether these two mitochondrial properties could explain differences in longevity. We report no relationship between membrane PI and MRL in populations of A. islandica, as well as a lack of intraspecific relationship between ETS complex activities and MRL. Individuals from brackish sites characterized by wide temperature and salinity windows had, however, markedly lower ETS enzyme activities relative to citrate synthase activity. Our results highlight environment-dependent remodeling of mitochondrial phenotypes.

Bio- and lithostratigraphy of lower Pleistocene marine successions in western Emilia (Italy) and their implications for the first occurrence of Arctica islandica in the Mediterranean Sea

AbstractThe Arda and Stirone marine successions (Italy) represent key sections for the early Pleistocene; they were deposited continuously within a frame of climate change, recording the Calabrian cooling as testified by the occurrence of the “northern guests,” such as the bivalve Arctica islandica. In addition, although the first occurrence of A. islandica in the Mediterranean Sea was used as the main criterion to mark the former Pliocene-Pleistocene boundary, the age of this bioevent was never well constrained. Here, we describe the Stirone depositional environment and constrain for the first time the section age using calcareous nannofossil and foraminifera biostratigraphy. We also correlate the Arda and Stirone sections using complementary biostratigraphic and magnetostratigraphic data. Our results indicate that A. islandica first occurred in both the successions slightly below the top of the CNPL7 biozone (dated at 1.71 Ma). Comparisons with other lower Pleistocene Mediterranean marine successions indicate that the stratigraphically lowest level where A. islandica first occurred in the Mediterranean Sea is in the Arda and Stirone sections; these environments satisfied the ecological requirements for the establishment and the proliferation of the species, which only subsequently (late Calabrian) has been retrieved in southern Italy and other areas of the Mediterranean Sea.

In situ Measurements of pH, CA2+, and Dic Dynamics within the Extrapallial Fluid of the Ocean Quahog Arctica islandica

This study investigated to what extent the extrapallial fluid (EPF) of the marine bivalve Arctica islandica (Linneaus, 1767) is involved in shell formation. With in situ pH microscopy, pH gradients were identified between inner shell surface and outer mantle epithelium (OME). pH at the OMEvaried rapidly between neutral and values above 9, suggesting active H+ pumping. Microsensor measurements showed also remarkable short-term dynamics in pH and Ca2+ concentrations, again suggesting active ion pumping. Further focus was on pH, Ca2+, and dissolved inorganic carbon dynamics within the EPF to determine whether calcium carbonate precipitation is possible within the EPF. The data show that the bulk of the inner EPF rarely reaches calcium carbonate saturation and, thus, cannot be the site of shell formation. At the OME surface, however, pH levels of up to 9.5 were observed, corresponding to a 30-fold carbonate supersaturation. Thus, ion pumping by the OME can drive calcification when the OME is just a few mm distant from the inner shell surface, as it is the case in the outer EPF.

Pacific climate influences on ocean conditions and extreme shell growth events in the Northwestern Atlantic (Gulf of Maine)

The Gulf of Maine is undergoing rapid environmental and ecological changes, yet our spatial and temporal understanding of the climatic and hydrographic variability in this region, including extreme events, is limited and biased to recent decades. In this study, we utilize a highly replicated, multi-century master shell growth chronology derived from the annual increments formed in the shells of the long-lived bivalve Arctica islandica collected in 38 m from the central coastal region in the Gulf of Maine. Our results indicate that shell growth is highly synchronous and inversely related to local seawater temperatures. Using composite analyses of extreme shell growth events from CE 1900 to 2013, we extend our understanding of the factors driving oceanic variability and shell growth in the Northwestern Atlantic back to CE 1761. We suggest that extreme shell growth events are primarily controlled by Gulf of Maine sea surface temperature (SST) and stratification conditions, which in turn appear to be largely influenced by SST patterns in the Pacific Ocean through their influence on mid-latitude atmospheric circulation patterns and the location of the eddy-driven jet. The large-scale jet dynamics during these extreme years manifest as precipitation and moisture transport anomalies and regional SST conditions in the Gulf of Maine that either enhance or inhibit shell growth. Pacific climate variability is thus an important, yet understudied, influence on Gulf of Maine ocean conditions.

Energetics of the extremely long-living bivalve Arctica islandica based on a Dynamic Energy Budget model

The ocean quahog Arctica islandica is the longest–living mollusk on Earth with a lifespan of at least 500 years. The slow senescence of this bivalve has promoted a great interest in its metabolic strategy. A dynamic energy budget (DEB) model was applied to describe how this species allocates its energy to maintenance, growth, maturation, and reproduction in a variable environment. We studied the relationship between A. islandica growth, lifespan, and food availability at eight different locations in the North Atlantic Ocean. Our results indicate that A. islandica's extreme longevity arises from its low somatic maintenance cost ṗM and low ageing acceleration h¨a, but there was not a direct relationship between food availability and lifespan in these A. islandica locations. Monkey Bank (North Sea), Iceland, and Ingøya (northern Norway) had the highest food availability estimates of all the localities but did not have the lowest longevities, in contrast to the theory of caloric restriction.

Biomineral Reactivity: The Kinetics of the Replacement Reaction of Biological Aragonite to Apatite

We present results of bioaragonite to apatite conversion in bivalve, coral and cuttlebone skeletons, biological hard materials distinguished by specific microstructures, skeletal densities, original porosities and biopolymer contents. The most profound conversion occurs in the cuttlebone of the cephalopod Sepia officinalis, the least effect is observed for the nacreous shell portion of the bivalve Hyriopsis cumingii. The shell of the bivalve Arctica islandica consists of cross-lamellar aragonite, is dense at its innermost and porous at the seaward pointing shell layers. Increased porosity facilitates infiltration of the reaction fluid and renders large surface areas for the dissolution of aragonite and conversion to apatite. Skeletal microstructures of the coral Porites sp. and prismatic H. cumingii allow considerable conversion to apatite. Even though the surface area in Porites sp. is significantly larger in comparison to that of prismatic H. cumingii, the coral skeleton consists of clusters of dense, acicular aragonite. Conversion in the latter is sluggish at first as most apatite precipitates only onto its surface area. However, the process is accelerated when, in addition, fluids enter the hard tissue at centers of calcification. The prismatic shell portion of H. cumingii is readily transformed to apatite as we find here an increased porosity between prisms as well as within the membranes encasing the prisms. In conclusion, we observe distinct differences in bioaragonite to apatite conversion rates and kinetics depending on the feasibility of the reaction fluid to access aragonite crystallites. The latter is dependent on the content of biopolymers within the hard tissue, their feasibility to be decomposed, the extent of newly formed mineral surface area and the specific biogenic ultra- and microstructures.

Lack of association between genetical and morphological variations for bivalve Arctica islandica from six different sites of the NE Atlantic ocean

The ocean quahog Arctica islandica is equally attractive to physiologists and environmental scientists due to its long life span of up to 400 years . For physiology, A. islandica is an exciting age model whereas environmental sciences infer past environmental conditions from morphometric and biogeochemical properties of the calcareous shell. In order to evaluate whether and animals from different localities differ, the present study compared genetics and morphometry of six A. islandica populations, from the Norwegian Coast, Kattegat, Kiel bay, White Sea, German Bight and Off Ne Iceland. For genetics, present research found 30 haplotypes of the mitochondrial cytochrome B (cyt B) gene, of which some are widely distributed, whereas others are quite rare. There is no consistent geographical pattern in haplotype distribution, even when a further previously published 11 haplotypes are taken into account. For morphometry, discriminant analysis indicated significant morphometric differences, e.g. in shell shape, between populations which are independent of geographical distance. Moreover, genetic and morphometric patterns appear to be unrelated. Thus, present study reveals morphological differences between populations of A. islandica appear to be driven by the environment rather than underlying genetic differences between populations.

Reprint of Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?

The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13Ccarbonate) and oxygen (δ18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation=0.65‰), approximately four times more variable than analytical precision.High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level.Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series.

Unexpected isotopic variability in biogenic aragonite: A user issue or proxy problem?

Abstract The present study seeks to investigate sources of isotopic variability in the commonly used paleoclimate archive, the marine bivalve Arctica islandica, with an emphasis on the potential of human-induced variability arising from sampling techniques. Stable carbon (δ13Ccarbonate) and oxygen (δ18Ocarbonate) isotopes were analyzed for split (intra-sample) and replicate (intra- and inter-shell) samples taken from a group of laboratory-reared individuals, a natural population from northern Norway, and a natural population from the Gulf of Maine, USA. Compared to analytical uncertainty of 0.17‰ and 0.30‰ for δ13C and δ18O, respectively, among the natural populations, the mean difference between shell splits and shell replicates ranged from 0.12‰ and 0.33‰ for δ13C and δ18O, respectively. Our data suggest that heterogeneity of the carbonate material (i.e., large range of isotopic composition within one sample due to seasonal environmental variability) may contribute to “unexpected” variability more than human-induced error from sampling imprecision when collecting whole annual increments. Furthermore, δ13C from juvenile shells were highly variable (2σ standard deviation = 0.65‰), approximately four times more variable than analytical precision. High precision among δ18O measurements of the laboratory-reared shells confirm the presumption that shells reliably and consistently precipitate in isotopic equilibrium with ambient seawater. Monte Carlo simulations of measurements from this population allowed characterization of improvements in uncertainty at increasing levels of replication. Substantial reduction in uncertainty occurs when increasing from two to three shells, however replication using a total of four shells further decreased uncertainty to within the 99% confidence level. Published studies sometimes compensate for uncertainties by replicating records over multiple individuals or multiple transects within the one individual. Oftentimes, however, isotope records are constructed from single individuals or transects and therefore fail to provide thorough estimates of proxy error. Our findings suggest that replication of carbon and oxygen isotope measurements of contemporaneously produced aragonite is necessary in order to reduce proxy-derived noise. Furthermore, population-specific estimates of uncertainty related to natural variability among individuals should be investigated in order to provide more realistic representations of proxy noise when reporting isotope time series.

Exploring the impact of diagenesis on (isotope) geochemical and microstructural alteration features in biogenic aragonite

AbstractFor the Quaternary and Neogene, aragonitic biogenic and abiogenic carbonates are frequently exploited as archives of their environment. Conversely, pre‐Neogene aragonite is often diagenetically altered and calcite archives are studied instead. Nevertheless, the exact sequence of diagenetic processes and products is difficult to disclose from naturally altered material. Here, experiments were performed to understand biogenic aragonite alteration processes and products. Shell subsamples of the bivalve Arctica islandica were exposed to hydrothermal alteration. Thermal boundary conditions were set at 100°C, 175°C and 200°C. These comparably high temperatures were chosen to shorten experimental durations. Subsamples were exposed to different 18O‐depleted fluids for durations between two and twenty weeks. Alteration was documented using X‐ray diffraction, cathodoluminescence, fluorescence and scanning electron microscopy, as well as conventional and clumped isotope analyses. Experiments performed at 100°C show redistribution and darkening of organic matter, but lack evidence for diagenetic alteration, except in Δ47 which show the effects of annealing processes. At 175°C, valves undergo significant aragonite to calcite transformation and neomorphism. The δ18O signature supports transformation via dissolution and reprecipitation, but isotopic exchange is limited by fluid migration through the subsamples. Individual growth increments in these subsamples exhibit bright orange luminescence. At 200°C, valves are fully transformed to calcite and exhibit purple‐blue luminescence with orange bands. The δ18O and Δ47 signatures reveal exchange with the aqueous fluid, whereas δ13C remains unaltered in all experiments, indicating a carbonate‐buffered system. Clumped isotope temperatures in high‐temperature experiments show compositions in broad agreement with the measured temperature. Experimentally induced alteration patterns are comparable with individual features present in Pleistocene shells. This study represents a significant step towards sequential analysis of diagenetic features in biogenic aragonites and sheds light on reaction times and threshold limits. The limitations of a study restricted to a single test organism are acknowledged and call for refined follow‐up experiments.

Environmental factors regulating gaping activity of the bivalve Arctica islandica in Northern Norway

Arctica islandica is the longest-living non-colonial animal known at present. It inhabits coastal waters in the North Atlantic and its annual shell increments are widely used for paleoclimatic reconstructions. There is no consensus, however, about the intra-annual timing of its feeding activity and growth. This research aims to identify the main environmental drivers of A. islandica valve gape to clarify the ambiguity surrounding its seasonal activity. A lander was deployed from February 2014 to September 2015 on the sea bottom at Ingøya, Norway (71°03′N, 24°05′E) containing living A. islandica specimens (70.17 ± 0.95 mm SE) in individual containers. Each individual was attached to an electrode unit that measured the distance between their valves (valve gape) every minute. Individuals were followed for various lengths of time, and in some cases replaced by smaller individuals (54.34 ± 0.63 mm SE). The lander was also equipped with instruments to simultaneously monitor temperature, salinity, [Chl-a], turbidity, and light. There was a significant difference in the average monthly valve gape (P value < 0.01), with monthly means of 19–84% of the total valve gape magnitude. The experimental population was largely inactive October–January, with an average daily gape <23%. During this period the clams opened at high amplitude once or twice a month for 1–3 days. Seasonal cycles of sea water temperature and [Chl-a] were temporally offset from each other, with temperature lagging [Chl-a] by about 2 months. Multiple regression analyses showed that bivalve gaping activity was most closely correlated with variable [Chl-a], and to a much smaller degree with photoperiod and temperature.

Lipofuscin accumulation in tissues of Arctica islandica indicates faster ageing in populations from brackish environments

Environmental factors can affect the rate of ageing and shape the lifespan in marine ectotherms. The mechanisms and the degree of - environmental influence on aging can best be studied in species with wide ranging biogeographic distribution. One of the biomarkers of physiological ageing is the fluorescent age pigment lipofuscin, which accumulates over lifetime in tissues of bivalves. We compared lipofuscin accumulation rate in muscles and respiratory tissues of the extremely long lived bivalve Arctica islandica from five geographically distinct populations (Northern Norway, White Sea, Kiel Bay, German Bight and Iceland). Maximum investigated chronological age across different populations in the present study differed from 40 years in Kiel Bay to 192 years at Iceland. An inverse association between lipofuscin deposition rate and recorded maximum age was observed through inter-population comparisons. In most cases lipofuscin accumulated exponentially over age in a tissue specific manner. The age specific lipofuscin content was significantly higher in respiratory than muscles tissues in all populations. Cellular lipofuscin granule area can be used as indicator of aging across A. islandica populations with the variance in granule accumulation depending on the annual variations of salinity in different marine regions, but not on the habitat specific thermal envelope.