Adamussium Research Articles

Stable carbon isotopes in scallop shells: A proxy of Antarctic sea-ice persistence

Sea ice is fundamental to global climate and its multiannual persistence or seasonal absence shapes Antarctic marine ecosystems. With sea ice in rapid decline in the Southern Ocean, it is imperative to understand its variability prior to satellite data. The Antarctic scallop Adamussium colbecki has a broad geographic distribution and long fossil history in the Southern Ocean, and its shells could be ideal bioarchives for sea ice with the potential to resolve subannual sea-ice dynamics over multiple years or decades. Here, we evaluate stable isotopes of carbon in A. colbecki shells from two sites on western McMurdo Sound. Each site maintains stable, frigid seawater temperatures, but they differ in sea-ice duration. Explorers Cove has semi-permanent multiannual sea ice, whereas Bay of Sails has annual sea ice that breaks out every year. Our results indicate that seasonal variation in δ13Cshell values may proxy sea-ice persistence. Scallops living under annual sea ice — adults from Bay of Sails and juveniles collected during a fortuitous recent sea ice breakout at Explorers Cove — had higher δ13Cshell values during summer growth than winter growth. Scallops living under multi-annual sea ice had no difference in δ13Cshell values between winter and summer growth. We posit that phytoplankton blooms leverage the seasonal δ13C values of the dissolved inorganic carbon under ice-free conditions, which is in turn recorded in δ13Cshell values and that A. colbecki shells could be used to understand past variability in sea-ice persistence in coastal Antarctica.

Individual diet variability shapes the architecture of Antarctic benthic food webs

Antarctic biodiversity is affected by seasonal sea-ice dynamics driving basal resource availability. To (1) determine the role of intraspecific dietary variability in structuring benthic food webs sustaining Antarctic biodiversity, and (2) understand how food webs and the position of topologically central species vary with sea-ice cover, single benthic individuals’ diets were studied by isotopic analysis before sea-ice breakup and afterwards. Isotopic trophospecies (or Isotopic Trophic Units) were investigated and food webs reconstructed using Bayesian Mixing Models. As nodes, these webs used either ITUs regardless of their taxonomic membership (ITU-webs) or ITUs assigned to species (population-webs). Both were compared to taxonomic-webs based on taxa and their mean isotopic values. Higher resource availability after sea-ice breakup led to simpler community structure, with lower connectance and linkage density. Intra-population diet variability and compartmentalisation were crucial in determining community structure, showing population-webs to be more complex, stable and robust to biodiversity loss than taxonomic-webs. The core web, representing the minimal community ‘skeleton’ that expands opportunistically while maintaining web stability with changing resource availability, was also identified. Central nodes included the sea-urchin Sterechinus neumayeri and the bivalve Adamussium colbecki, whose diet is described in unprecedented detail. The core web, compartmentalisation and topologically central nodes represent crucial factors underlying Antarctica’s rich benthic food web persistence.

The dynamics of growth and maturation age in the scallop Adamussium colbecki in Tera Nova Bay, Antarctica

The endemic Antarctic scallop Adamussium colbecki, one of the most common bivalve species, plays an important ecological role in Antarctic ecosystems. In this study, we investigated the size frequency structure, shell height, and gonadosomatic index (GSI) of A. colbecki in coastal areas near Jang Bogo Antarctic Research Station in Terra Nova Bay. A generalized von Bertalanffy growth function was fitted to shell height-at-age measurements of 389 individuals (H∞ = 115.4 mm and K = 0.064 year−1). Large-sized individuals (70–84 mm) of A. colbecki were ∼2X as prevalent, accounting for more than 50% of the overall density. Individuals younger than 6 years showed a lower growth rate compared to that reported in previous studies. GSI indicated that sexual maturity of both females and males was observed in individuals over 50 mm shell height at the age of approximately 9 years. The maturity was delayed by two to four years when compared with previous data in Terra Nova Bay due to the low growth rates of the young population. Therefore, the low growth rate of young individuals and the delayed maturity age may have deleterious effects on population growth. The information reported here provides baseline scientific data that can be used to develop better informed management decisions and aid in defining an effective management strategy for Antarctic scallops.

The Antarctic Scallop Adamussium colbecki Is Unable to Transcriptomically Respond to Captivity and Moderate Thermal Stress

Adamussium colbecki is a scallop endemic of the Antarctic Ocean, the only modern survivor of the Adamussiini tribe and one of the few bivalves living in polar environments. Compared with other Antarctic animals, very little is known concerning the evolutionary adaptations which allow this species to thrive at sub-zero temperatures. Due to its local abundance and sensitivity to environmental changes, A. colbecki is an interesting model for studying the effects of pollution and climate change in the Antarctic Ocean. Here, we report, for the first time, the application of transcriptomic tools to the study of the effects of a short-to-medium term exposure to a +1.5 °C water temperature increase on three tissues. Although this approach did not highlight any significant change in response to thermal stress, we observed slight alterations in energetic metabolism and nutrient adsorption in the digestive gland, most likely linked with stabling in experimental tanks. The results of our study suggest that A. colbecki may be particularly vulnerable to the effects of climate change due to its complete inability to adapt to temperature increase at the transcriptomic level.

Comparative Transcriptomic Analysis Reveals Adaptive Traits in Antarctic Scallop Adamussium colbecki

Antarctica is the most extreme continent of Earth, with strong winds, freezing temperatures on land, and ocean temperatures constantly below 0 °C. Nonetheless, the Antarctic Ocean is home to an astounding diversity of living organisms that adapted to the multiple challenges posed by this environment via a diverse set of evolutionary traits. Although the recent advancements in sequencing technologies clarified the molecular bases of such adaptations in Antarctic fishes, little information is available for Antarctic invertebrates. In this preliminary study, we address this knowledge gap with a comparative transcriptomic approach to obtain insights into some of the adaptations that allow the Antarctic scallop Adamussium colbecki to survive and thrive in the freezing waters of the Antarctic Ocean. Despite some limitations, our analyses highlighted significant over-expression of genes involved in regulation of mRNA transcription, maturation, and degradation, which might compensate for a reduced efficiency of these processes at low temperatures. Other alterations detected in the Antarctic scallop transcriptome include enhanced expression of genes that regulate degradation of misfolded protein products and allow maintenance of cytoskeletal structure and function at subzero temperatures. Altogether, these observations support the presence of multiple previously unreported molecular adaptive traits in A. colbecki, which have important implications for our understanding of adaptation of this important component of the Antarctic trophic chain to such an extreme, but stable environment.

Cryofouling avoidance in the Antarctic scallop Adamussium colbecki

The presence of supercooled water in polar regions causes anchor ice to grow on submerged objects, generating costly problems for engineered materials and life-endangering risks for benthic communities. The factors driving underwater ice accretion are poorly understood, and passive prevention mechanisms remain unknown. Here we report that the Antarctic scallop Adamussium colbecki appears to remain ice-free in shallow Antarctic marine environments where underwater ice growth is prevalent. In contrast, scallops colonized by bush sponges in the same microhabitat grow ice and are removed from the population. Characterization of the Antarctic scallop shells revealed a hierarchical micro-ridge structure with sub-micron nano-ridges which promotes directed icing. This concentrates the formation of ice on the growth rings while leaving the regions in between free of ice, and appears to reduce ice-to-shell adhesion when compared to temperate species that do not possess highly ordered surface structures. The ability to control the formation of ice may enable passive underwater anti-icing protection, with the removal of ice possibly facilitated by ocean currents or scallop movements. We term this behavior cryofouling avoidance. We posit that the evolution of natural anti-icing structures is a key trait for the survival of Antarctic scallops in anchor ice zones.

Striae in the Antarctic scallop Adamussium colbecki provide environmental insights but not reliable age increments

Subannual growth increments in bivalves provide insight into past seasonal seawater conditions at high temporal resolution. The Antarctic scallop Adamussium colbecki (Smith 1902) accretes putatively fortnightly surficial growth lines (striae) and interstrial growth increments have the potential to archive sea ice variations. Cycles of paired groups of wide and narrow striae are sometimes used to determine ontogenetic age in these scallops, but previous quantitative work describing strial grouping and formation is limited to a few months of juvenile growth. Here, we analyze striae patterns in A. colbecki collected from two sites on western McMurdo Sound, Antarctica that differ by sea ice duration: Explorers Cove with multi-annual sea ice and Bay of Sails with annual sea ice. At both sites, visual analysis of striae groups and cycles (using the methods of previous authors) and wavelet analysis of interstrial increments suggest that striae groups are too variable to age A. colbecki. Only ~ 40% of striae groups and cycles conformed to expectations from annual cycles of fortnightly growth increments (~ 26 striae per cycle). Moreover, only one scallop from each study site displayed consistent periodicity at ~ 26 striae throughout juvenile growth in wavelet analysis. Though striae grouping was inconsistent, analysis of concurrent growth of juvenile scallops from Explorers Cove suggested strong environmental control on interstrial increment size and thus that strial increments are suitable for further analysis as sea ice proxies. Finally, the multi-annual sea ice site had smaller interstrial growth increments and less valve wear than the annual sea ice site, indicating overall slower growth and possibly lower metabolic activity.

Seasonal Food Web Dynamics in the Antarctic Benthos of Tethys Bay (Ross Sea): Implications for Biodiversity Persistence Under Different Seasonal Sea-Ice Coverage

Determining food web architecture and its seasonal cycles is a precondition for making predictions about Antarctic marine biodiversity under varying climate change scenarios. However, few scientific data concerning Antarctic food web structure, the species playing key roles in web stability and the community responses to changes in sea-ice dynamics are available. Based on C and N stable isotope analysis, we describe Antarctic benthic food webs and the diet of species occurring in shallow waters (Tethys Bay, Ross Sea) before and after seasonal sea-ice break-up. We hypothesized that the increased availability of primary producers (sympagic algae) following sea-ice break-up affects the diet of species and thus food web architecture. Basal resources had distinct isotopic signatures that did not change after sea-ice break-up, enabling a robust description of consumer diets based on Bayesian mixing models. Sympagic algae had the highest δ13C (∼−14‰) and red macroalgae the lowest (∼−37‰). Consumer isotopic niches and signatures changed after sea-ice break-up, reflecting the values of sympagic algae. Differences in food web topology were also observed. The number of taxa and the number of links per taxon were higher before the thaw than after it. After sea-ice break-up, sympagic inputs allowed consumers to specialize on abundant resources at lower trophic levels. Foraging optimization by consumers led to a simpler food web, with lower potential competition and shorter food chains. However, basal resources and Antarctic species such as the bivalve Adamussium colbecki and the sea-urchin Sterechinus neumayeri were central and highly connected both before and after the sea-ice break-up, thus playing key roles in interconnecting species and compartments in the web. Any disturbance affecting these species is expected to have cascading effects on the entire food web. The seasonal break-up of sea ice in Antarctica ensures the availability of resources that are limiting for coastal communities for the rest of the year. Identification of species playing a key role in regulating food web structure in relation to seasonal sea-ice dynamics, which are expected to change with global warming, is central to understanding how these communities will respond to climate change.

Growth and longevity of the Antarctic scallopAdamussium colbeckiunder annual and multiannual sea ice

AbstractEcosystem engineers such as the Antarctic scallop (Adamussium colbecki) shape marine communities. Thus, changes to their lifespan and growth could have far-reaching effects on other organisms. Sea ice is critical to polar marine ecosystem function, attenuating light and thereby affecting nutrient availability. Sea ice could therefore impact longevity and growth in polar bivalves unless temperature is the overriding factor. Here, we compare the longevity and growth ofA. colbeckifrom two Antarctic sites: Explorers Cove and Bay of Sails, which differ by sea-ice cover, but share similar seawater temperatures, the coldest on Earth (-1.97°C). We hypothesize that scallops from the multiannual sea-ice site will have slower growth and greater longevity. We found maximum ages to be similar at both sites (18–19 years). Growth was slower, with higher inter-individual variability, under multiannual sea ice than under annual sea ice, which we attribute to patchier nutrient availability under multiannual sea ice. Contrary to expectations,A. colbeckigrowth, but not longevity, is affected by sea-ice duration when temperatures are comparable. Recent dramatic reductions in Antarctic sea ice and predicted temperature increases may irrevocably alter the life histories of this ecosystem engineer and other polar organisms.

In Situ Geochemical Analysis of Organics in Growth Lines of Antarctic Scallop Shells: Implications for Sclerochronology

Bivalve shells are extensively used as bioarchives for paleoclimate and paleoenvironmental reconstructions. Proxy calibrations in recent shells are the basis for sclerochronology and the applications of geochemistry data to fossils. Shell geochemical information, however, could be altered with the disappearance of intercrystalline organic matrix components, including those linked to shell growth increments, during early diagenesis. Thus, an evaluation of the chemistry of such organics is needed for the correct use of sclerochronological records in fossil shells. Here, we use atom probe tomography (APT) for in situ geochemical characterization of the insoluble organic matrix in shell growth increments in the Antarctic scallop, Adamussium colbecki. We confirm the presence of carboxylated S-rich proteoglycans, possibly involved in calcite nucleation and growth in these scallops, with significant concentrations of magnesium and calcium. Diagenetic modification of these organic components could impact proxy data based on Mg/Ca ratios, but more importantly the use of the δ15N proxy, since most of the shell nitrogen is likely bound to the amide groups of proteins. Overall, our findings reinforce the idea that shell organics need to be accounted for in the understanding of geochemical proxies.

Robustness of Adamussium colbecki shell to ocean acidification in a short-term exposure

Atmospheric pCO2 has increased since the industrial revolution leading to a lowering of the ocean surface water pH, a phenomenon called ocean acidification (OA). OA is claimed to be a major threat for marine organisms and ecosystems and, particularly, for Polar regions. We explored the impact of OA on the shell mechanical properties of the Antarctic scallop Adamussium colbecki exposed for one month to acidified (pH 7.6) and natural conditions (unmanipulated littoral water), by performing Scanning Electron Microscopy, nanoindentation and Vickers indentation on the scallop shell. No effect of pH could be detected either in crystal deposition or in the mechanical properties. A. colbecki shell was found to be resistant to OA, which suggests this species to be able to face a climate change scenario that may threat the persistence of the endemic Antarctic species. Further investigation should be carried out in order to elucidate the destiny of this key species in light of global change.

Oceanographic moorings as year-round laboratories for investigating growth performance and settlement dynamics in the Antarctic scallop Adamussium colbecki (E. A. Smith, 1902).

BackgroundOceanographic moorings (OMs) are standard marine platforms composed of wires, buoys, weights and instruments, and are used as in situ observatories to record water column properties. However, OMs are also comprised of hard substrates on which a variety of invertebrates can settle when they encounter these structures along their dispersal routes. In this contribution, we studied the fouling communities found on two OMs deployed in the Ross Sea (Antarctica). Furthermore, a cage containing the Antarctic scallop Adamussium colbecki (E. A. Smith, 1902) was incorporated in the OM. The growth of the caged A. colbecki were evaluated after 1 year and their shells used as biological proxy for seawater temperature and salinity.MethodsA variety of settlers were collected from two different OMs deployed in the Ross Sea (Antarctica) and species identified using a combination of morphological and genetic (mainly through DNA barcoding) characteristics. Caged scallops were individually marked with permanent tags and their growth studied in terms of size-increment data (SID). Cages were specifically designed to prevent damage to individuals due to water drag during OM deployment and retrieval. Growth parameters from the caged individuals were applied to the A. colbecki juveniles that had settled on the mooring, to trace the likely settlement period.ResultsThe growth performance of caged A. colbecki was similar to that from previous growth studies of this species. The remarkable survival rate of caged specimens (96.6%) supports the feasibility of caging experiments, even for a species with a fragile shell such as the Antarctic scallop. Some of the new recruits found on the mooring were A. colbecki, the same species we put into special cages fixed to it. The settlement of the A. colbecki juveniles started during the Austral spring with a peak in summer months and, remarkably, coincided with seasonal changes in water temperature and flow direction, which were recorded by the mooring’s instruments. Genetic data from other settlers provided new information about their larval ecology and connectivity.DiscussionOceanographic moorings are expensive and complex experimental platforms that, at present, are strictly used for the acquisition of physical and biogeochemical data. Their use for in situ ecological experiments on model organisms suitable for caging and to study fouling species has yet to be fully explored. We present the outcomes of a study, which represents a baseline for the characterization of Antarctic fouling biodiversity. We hope that in the near future an internationally coordinated systematic study of settlers could be initiated around the Antarctic continent. This could utilize “new generation OMs” equipped with standardized settlement structures and agreed sampling protocols for the study of fouling communities.

The impact of ocean acidification on the gonads of three key Antarctic benthic macroinvertebrates

CO2 atmospheric pressure is increasing since industrial revolution, leading to a lowering of the ocean surface water pH, a phenomenon known as ocean acidification, with several reported effects on individual species and cascading effects on marine ecosystems. Despite the great amount of literature on ocean acidification effects on calcifying organisms, the response of their reproductive system still remains poorly known. In the present study, we investigated the histopathological effects of low pH on the gonads of three key macroinvertebrates of the Terra Nova Bay (Ross Sea) littoral area: the sea urchin Sterechinus neumayeri, the sea star Odontaster validus and the scallop Adamussium colbecki. After 1 month of exposure at control (8.12) and reduced (7.8 and 7.6) pH levels, we dissected the gonads and performed histological analyses to detect potential differences among treatments. Results showed significant effects on reproductive conditions of A. colbecki and S. neumayeri, while O. validus did not show any kind of alteration. Present results reinforce the need to focus on ocean acidification effects on soft tissues, particularly the gonads, whose damage may exert large effects on the individual fitness, with cascading effects on the population dynamic of the species.

New insights into the genome repetitive fraction of the Antarctic bivalve Adamussium colbecki.

Repetitive DNA represents the major component of the genome in both plant and animal species. It includes transposable elements (TEs), which are dispersed throughout the genome, and satellite DNAs (satDNAs), which are tandemly organized in long arrays. The study of the structure and organization of repetitive DNA contributes to our understanding of genome architecture and the mechanisms leading to its evolution. Molluscs represent one of the largest groups of invertebrates and include organisms with a wide variety of morphologies and lifestyles. To increase our knowledge of bivalves at the genome level, we analysed the Antarctic scallop Adamussium colbecki. The screening of the genomic library evidenced the presence of two novel satDNA elements and the CvA transposon. The interspecific investigation performed in this study demonstrated that one of the two satDNAs isolated in A. colbecki is widespread in polar molluscan species, indicating a possible link between repetitive DNA and abiotic factors. Moreover, the transcriptional activity of CvA and its presence in long-diverged bivalves suggests a possible role for this ancient element in shaping the genome architecture of this clade.

Time- and depth-wise trophic niche shifts in Antarctic benthos.

Climate change is expected to affect resource-consumer interactions underlying stability in polar food webs. Polar benthic organisms have adapted to the marked seasonality characterising their habitats by concentrating foraging and reproductive activity in summer months, when inputs from sympagic and pelagic producers increase. While this enables the persistence of biodiverse food webs, the mechanisms underlying changes in resource use and nutrient transfer are poorly understood. Thus, our understanding of how temporal and spatial variations in the supply of resources may affect food web structure and functioning is limited. By means of C and N isotopic analyses of two key Antarctic benthic consumers (Adamussium colbecki, Bivalvia, and Sterechinus neumayeri, Echinoidea) and Bayesian mixing models, we describe changes in trophic niche and nutrient transfer across trophic levels associated with the long- and short-term diet and body size of specimens sampled in midsummer in both shallow and deep waters. Samplings occurred soon after the sea-ice broke up at Tethys Bay, an area characterised by extreme seasonality in sea-ice coverage and productivity in the Ross Sea. In the long term, the trophic niche was broader and variation between specimens was greater, with intermediate-size specimens generally consuming a higher number of resources than small and large specimens. The coupling of energy channels in the food web was consequently more direct than in the short term. Sediment and benthic algae were more frequently consumed in the long term, before the sea-ice broke up, while consumers specialised on sympagic algae and plankton in the short term. Regardless of the time scale, sympagic algae were more frequently consumed in shallow waters, while plankton was more frequently consumed in deep waters. Our results suggest a strong temporal relationship between resource availability and the trophic niche of benthic consumers in Antarctica. Potential climate-driven changes in the timing and quality of nutrient inputs may have profound implications for the structure of polar food webs and the persistence of their constituent species, which have adapted their trophic niches to a highly predictable schedule of resource inputs.

Predation impact of the notothenioid fish Trematomus bernacchii on the size structure of the scallop Adamussium colbecki in Terra Nova Bay (Ross Sea, Antarctica)

Biotic interactions are particularly relevant in stable environments, such as the High Antarctic areas. Among them, predation has a key role in structuring community and population variables, including size-frequency distribution. This study aims to quantify the impact of predation by the notothenioid fish Trematomus bernacchii on the Antarctic scallop Adamussium colbecki-size distribution. We developed a model of this impact that estimates the size distribution of the preyed scallop population, taking into account for the predator-size distribution, sex structure, and daily consumption. Comparing this size distribution of the preyed A. colbecki with the living populations at Terra Nova Bay (Ross Sea, Antarctica), we were able to detect a relevant impact of fish predation. Fish-size frequency resulted to be the major factor shaping prey-size structure, with significant differences between predation by males and females. Our findings, given the key role of the two species in the littoral ecosystem of Terra Nova Bay (Antarctic Special Protected Area 161), fall into the framework of ecosystem management of High Antarctic coastal areas, particularly in the actual context of climate change, and increasing anthropogenic impact.

Fossil bivalves in marine sediments of Vestfold Hills in Eastern Antarctica

Bivalves collected in Vestfold Hills during the 55th Russian Antarctic Expedition (RAE, 2009−2010) are represented by five species. Four of them (Laternula elliptica, Thracia meridionalis, Adamussium colbecki, and Philobrya sublaevis) were collected in the sediments that filled the coastal lake terraces during the Holocene; these species are still abundant on the Antarctic shelf at present. Bivalves were found in eight samples, with L. elliptica shells and fragments thereof found in seven of those samples. The sample collected near Deep Lake had the most diverse species composition, as it contained all four species named above. Shells of named species widely occurring in present-day Antarctica were found high above sea level in the marine sediments of the oasis. This indicate to the similarity of the oasis habitats in the past and the recent marine conditions. Fragments of shells of the fifth (now extinct) species Ruthipecten tuftsensis were found in glacial–marine sediments of the Marine Plain dating back to the late Pleistocene. The present study of fossil bivalves from the late Cenozoic marine sediments in Vestfold Hills is the first of its kind in Russia.

Retrospective biomonitoring of chemical contamination in the marine coastal environment of Terra Nova Bay (Ross Sea, Antarctica) by environmental specimen banking

Antarctica offers a good opportunity to investigate planetary-scale pollution and climate change, and provides baseline values for contaminants such as Trace Elements (TEs) and Persistent Organic Pollutants (POPs). Literature data on contaminant levels in the Antarctic environment indicate that long-range atmospheric transport is the primary pathway by which pollutants from surrounding continents are carried to this pristine environment. However, local contamination sources represented by the scientific stations are also not negligible. Climate change and global warming are altering the global budget of anthropogenic contaminants and their monitoring in Antarctica ecosystems is very important to protect the global environment.In this work, eighty specimens of Adamussium colbecki (Smith, 1902), a benthic Antarctic scallop, collected from 1996 to 2009 and stored in the Antarctic Environmental Specimen Bank, were analyzed to quantify TEs and POPs, including polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs) and polycyclic aromatic hydrocarbons (PAHs). Metals concentrations were not affected by anthropogenic contributions, highlighting a natural accumulation with the age of the organism. Similarly, no temporal trend was found for PCNs, PCBs and PAHs. However, specimens collected during the summer 1997–98 showed enhanced concentration levels of PCBs and PAHs that could refer to a local anthropogenic source of contamination.

BIOTURBATION BY THE COMMON ANTARCTIC SCALLOP (ADAMUSSIUM COLBECKI) AND OPHIUROID (OPHIONOTUS VICTORIAE) UNDER MULTI-YEAR SEA ICE: ECOLOGIC AND STRATIGRAPHIC IMPLICATIONS

The abundant epifaunal scallop Adamussium colbecki and ophiuroid Ophionotus victoriae bioturbate the seafloor under the multi-year sea ice in Explorers Cove, western McMurdo Sound, Antarctica by churning the upper few centimeters of the sandy substrate. Laboratory investigation of these animals' activities demonstrates that the scallops on average resuspend 45 cm3 d−1 ind−1 via water jets ejected during swimming and clapping movement and that the ophiuroids on average disrupt 861 cm3 d−1 ind−1 via rowing motion and self-burial in the upper centimeters of the substrate. At observed densities in Explorers Cove, bioturbation rates greatly exceed sediment accumulation rates and physical reworking processes, resulting in homogenized sediment lacking both lamination and discrete traces that would signal its biogenic modification. Adamussium colbecki employs water jets to resuspend the limited phytodetritus needed by the suspension-feeding scallop in the quiet sub-sea ice conditions and produces depressions ∼ 3 cm deep that increase substrate surface area and microtopography in Explorers Cove. The scallop thus acts as an ecosystem engineer, modifying the sediment and controlling the flux of materials between the substrate and water as it claps for food gathering rather than for predator evasion like other scallops. The resulting rapid, shallow diffuse bioturbation differs from the more commonly reported vertical bioturbation by infaunal animals recorded in cores, yet it exerts strong control on the sedimentary record and may be characteristic of low-energy, oligotrophic environments beneath multi-year sea ice around Antarctica where a lack of fast predators and low sedimentation rate allow proliferation of epifaunal animals.

Oxidative responsiveness to multiple stressors in the key Antarctic species, Adamussium colbecki: Interactions between temperature, acidification and cadmium exposure

High-latitude marine ecosystems are ranked to be among the most sensitive regions to climate change since highly stenothermal and specially adapted organisms might be seriously affected by global warming and ocean acidification. The present investigation was aimed to provide new insights on the sensitivity to such environmental stressors in the key Antarctic species, Adamussium colbecki, focussing also on their synergistic effects with cadmium exposure, naturally abundant in this area for upwelling phenomena. Scallops were exposed for 2 weeks to various combinations of Cd (0 and 40 μgL-1), pH (8.05 and 7.60) and temperature (−1 and +1 °C). Beside Cd bioaccumulation, a wide panel of early warning biomarkers were analysed in digestive glands and gills including levels of metallothioneins, individual antioxidants and total oxyradical scavenging capacity, onset of oxidative cell damage like lipid peroxidation, lysosomal stability, DNA integrity and peroxisomal proliferation. Results indicated reciprocal interactions between multiple stressors and their elaboration by a quantitative hazard model based on the relevance and magnitude of effects, highlighted a different sensitivity of analysed tissues. Due to cellular adaptations to high basal Cd content, digestive gland appeared more tolerant toward other prooxidant stressors, but sensitive to variations of the metal. On the other hand, gills were more affected by various combinations of stressors occurring at higher temperature.