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Noisy human activities at sea are changing the acoustic environment, which has been shown to affect marine mammals and fishes. Invertebrates, such as bivalves, have so far received limited attention despite their important role in the marine ecosystem. Several studies have examined the impact of sound on anti-predator behavior using simulated predators, but studies using live predators are scarce. In the current study, we examined the separate and combined effects of boat sound playback and predator cues of shore crabs (Carcinus maenas) on the behavior of mussels (Mytilus spp.). We examined the behavior of the mussels using a valve gape monitor and scored the behavior from the crabs in one of two types of predator test conditions from video footage to control for effects from potential, sound-induced variation in crab behavior. We found that mussels closed their valve gape during boat noise and with a crab in their tank, but also that the stimulus combination did not add up to an even smaller valve gape. The sound treatment did not affect the stimulus crabs, but the behavior of the crabs did affect the valve gape of the mussels. Future research is needed to examine whether these results stand in situ and whether valve closure due to sound has fitness consequences for mussels. The effects on the well-being of individual mussels from anthropogenic noise may be relevant for population dynamics in the context of pressure from other stressors, their role as an ecosystem engineer, and in the context of aquaculture.

Innovative techniques are needed to assess oyster performance in flat oyster reef restoration projects. A valve gape monitor, a device that continuously measures opening and closing of live bivalves, can potentially be used as an effective method to determine survival and behaviour of the European flat oyster Ostrea edulis. The method has been successfully used in combination with a number of bivalve species to investigate valve gape activity in response to environmental factors. In this study, eight O. edulis were equipped with valve gape sensors in order to relate gape to environmental conditions such as food availability. Valve gape activity was monitored under controlled laboratory conditions, with and without food, in a concrete basin in the Oosterschelde and in the field (Voordelta, Dutch North Sea). Under controlled laboratory conditions, oysters clearly responded to changes in food availability. Starved oysters closed their valves significantly longer than oysters that received food, and the relative gape width in fed oysters was larger. In the concrete basin (Oosterschelde), a positive correlation between valve opening and Chlorophyll-a was found. Additionally, valve gape activity and tidal movement appeared to be linked. When exposed to a full tidal cycle (Voordelta), a negative correlation between valve opening and Chlorophyll-a was found. However, there was no correlation between valve gape and current velocity. In autumn, longer periods of inactivity were seen, but when valves opened, the valve gape was larger. These data indicate that valve gape can provide valuable information on behaviour (gape frequency and gape width), but also show that it is not necessarily a good proxy for feeding rate. Nevertheless, these results show that the gape monitor can be used to determine the natural behaviour of flat oysters under field conditions, and that gape opening provides information on behaviour and the stress response of bivalves to environmental conditions.

Growth experiments present a powerful tool for determining the effect of environmental parameters on growth and carbonate composition in biogenic calcifiers. For successful proxy calibration and biomineralization studies, it is vital to exactly identify volumes of carbonate precipitated at precise intervals during the experiment. Here, we investigate the use of strontium labelling in mollusk growth experiments. Three bivalve species (C. edule, M. edulis and O. edulis) were grown under monitored field conditions. The bivalves were regularly exposed to seawater with elevated concentrations of dissolved strontium. In addition, the size of the shells was determined at various stages during the experiment using calliper measurements and digital photography. Trace element profiles were measured in cross sections through the shells of these mollusks using laser ablation ICP-MS and XRF techniques. Our results show that doses of dissolved strontium equivalent to 7-8 times the background marine value are sufficient to produce reproducible peaks in shell incorporated strontium in C. edule and M. edulis shells. No negative effects were observed on shell calcification rates. Lower doses (3-5 times background values) resulted in less clearly identifiable peaks, especially in M. edulis. Strontium spiking labels in shells of O. edulis are more difficult to detect, likely due to their irregular growth. Nevertheless, strontium spiking seems a useful technique for creating time marks in cultured shells and a reproducible way to monitor shell height along the growing season while limiting physical disturbance of the animals. However, accurate reconstructions of growth rates at high time resolution require frequent spiking with high doses of strontium.

Several species new to the area were collected while monitoring Dutch marine waters using a dredge. The varunid crab Asthenognathus atlanticus Monod, 1933 was recorded for the first time in the North Sea. Until 2008, this relatively rare crab was known from the west coast of Africa and the western Mediterranean to northern Brittany in the north. In recent years, its distribution range has expanded, as indicated by records from the Bay of the Seine and the area around Dieppe-Le Tréport. Our finding from Brown Bank (southern North Sea) indicates a further, northward expansion of its distribution range. We list the hosts with which the crab is associated. Earlier arguments for climate change as an explanation for the northward range expansion are supported.

Clumped isotope thermometry can independently constrain the formation temperatures of carbonates, but a lack of precisely temperature-controlled calibration samples limits its application on aragonites. To address this issue, we present clumped isotope compositions of aragonitic bivalve shells grown under highly controlled temperatures (1-18°C), which we combine with clumped isotope data from natural and synthetic aragonites from a wide range of temperatures (1-850°C). We observe no discernible offset in clumped isotope values between aragonitic foraminifera, mollusks, and abiogenic aragonites or between aragonites and calcites, eliminating the need for a mineral-specific calibration or acid fractionation factor. However, due to non-linear behavior of the clumped isotope thermometer, including high-temperature (100°C) datapoints in linear clumped isotope calibrations causes them to underestimate temperatures of cold (1-18°C) carbonates by 2.7 ± 2.0°C (95% confidence level). Therefore, clumped isotope-based paleoclimate reconstructions should be calibrated using samples with well constrained formation temperatures close to those of the samples.

Understanding the response of Earth’s climate to perturbations requires accurate and detailed reconstructions of past climate states (e.g. Tierney et al., 2020). The clumped isotope thermometer has the potential to constrain the formation temperatures of carbonates independent from the (isotopic) composition of the precipitation fluid and regardless of the origin (e.g. taxonomy) of the carbonate producer (e.g. Anderson et al., 2020), making it an ideal tool for paleoclimate reconstructions. Unfortunately, it is still not fully certain whether the clumped isotope composition of different carbonate minerals (e.g. calcite, aragonite, dolomite) responds similarly to changes in formation temperatures or variations in the temperature at which the acid reaction takes place during analyses (e.g. Guo et al., 2009; Müller et al., 2017). This uncertainty complicates the application of clumped isotope thermometry to biogenic aragonite shells of bivalves and gastropods, as well as to chemically precipitated travertines and speleothems.To solve part of these issues, we present a new dataset consisting of clumped isotope measurements on aragonitic Arctica islandica bivalves grown at precisely controlled temperatures (1.1±0.2°C - 18±0.3°C). We compare our data with preexisting clumped isotope calibration datasets spanning a wide temperature range and containing both aragonite and calcite samples. Our clumped isotope data with well-defined formation temperatures allows us to constrain small but important differences between previously published calibration datasets and sheds light on the temperature dependence of clumped isotope composition of aragonites. We use these new insights into the clumped isotope thermometer at low temperatures to produce seasonally resolved paleotemperature reconstructions from excellently preserved aragonitic bivalves from the Pliocene Warm Period, a valuable analogue for future climate under intermediate greenhouse gas emission scenarios (SSP2-4.5; Meinshausen et al., 2020).ReferencesAnderson et al. GRL 48, e2020GL092069, https://doi.org/10.1029/2020GL092069, 2021.Guo et al. GCA, 73, 7203–7225, https://doi.org/10.1016/j.gca.2009.05.071, 2009.Meinshausen et al. GMD 13, 3571–3605, https://doi.org/10.5194/gmd-13-3571-2020, 2020.Müller et al. Chem. Geol., 449, 1–14, https://doi.org/10.1016/j.chemgeo.2016.11.030, 2017.Tierney et al. Science 370, https://doi.org/10.1126/science.aay3701, 2020.

Anthropogenic sound has been shown to affect marine animals across taxa. However, bivalves and other invertebrates have received limited attention, and most studies across taxa have focussed on immediate, rather than long-term, effects of sound. Most bivalves adopt a sessile or sedentary lifestyle and are therefore likely to be subject to frequent exposure to the same anthropogenic sounds. For this reason, bivalves are an especially relevant taxonomic group to study with regards to potential long-term effects of sound. In the current study, we examined whether blue mussels ( Mytilus edulis ) habituate to repeated sound exposures and whether they recover quicker from a single pulse exposure than from a pulse train. We equipped individual mussels with sensors to monitor their valve gape and exposed them to repeated sound playback. We found that mussels responded to sound by partially closing their valves. This response was consistent and repeatable, and decayed over sequential exposures to the same sound stimulus. A stimulus specificity test, meant to determine whether the decayed response could be attributed to habituation or more general sensory adaptation, yielded interesting but ambiguous results. Additionally, we found no differences in the initial response and recovery (time to return to baseline levels) between mussels that were exposed to single pulses and pulse trains. Our results therefore show that mussels reduce responsiveness over sequential exposures and that mussels mostly respond to the onset of a pulse train. Future research is needed to determine whether mussels habituate in situ to actual anthropogenic sound and whether a lack of a behavioural response to repeated sound also implies a lack of other negative effects, such as physiological changes and mortality.

The pearl whipray

Geochemical records from incremental carbonate archives, such as fossil mollusk shells, contain information on climate and environmental change at the resolution of days to decades (e.g. Schöne and Gillikin, 2013; Ivany, 2012). These high-resolution paleoclimate data, providing snapshots of past climate change on a human scale, complement more conventional reconstructions on a geological timescale of thousands to millions of years. Recent innovations in geochemical techniques such as high-resolution trace element and clumped isotope analyses provide the unique potential to improve the accuracy and resolution of these high-resolution climate reconstructions in the near future (see e.g. de Winter et al., 2020a; b; Caldarescu et al., 2021). However, to be able to make the most out of these new techniques requires a more detailed understanding of the timing and mechanisms of mollusk shell growth as well as the relationship between environment and shell chemistry on daily to weekly timescales.The UNBIAS (UNravelling BIvAlve Shell chemistry) project combines investigations on lab-grown modern bivalve shells with reconstructions based on fossil shell material from past greenhouse periods in an attempt to improve our understanding of short-term temperature variability in warm climates. Samples from cultured shells labeled with a novel trace element spiking method are used to calibrate accurate temperature reconstructions from bivalve shells using the state-of-the-art clumped isotope method. As a result, we present a temperature calibration of clumped isotope measurements on aragonitic shell carbonates. New statistical routines are developed to accurately date microsamples within shells relative to the seasonal cycle (ShellChron; de Winter, 2020) and to strategically combine these microsamples for seasonal reconstructions of temperature and salinity from fossil shells (seasonalclumped, de Winter et al., 2020c; de Winter, 2021). We present the first results of this integrated seasonal reconstruction approach on fossil bivalve shells from the Pliocene Warm Period and Late Cretaceous greenhouse of northwestern Europe as well as an outlook on future plans within the UNBIAS project. ReferencesCaldarescu, D. E. et al. Geochimica et Cosmochimica Acta 294, 174–191 (2021).de Winter, N. J. ShellChron v0.2.8: Builds Chronologies from Oxygen Isotope Profiles in Shells. (2020).de Winter, N. J. seasonalclumped v0.3.2: Toolbox for Seasonal Temperature Reconstructions using Clumped Isotope Analyses. (2021).de Winter, N. J. et al. Paleoceanography and Paleoclimatology 35, e2019PA003723 (2020a).de Winter, N. J. et al. Nature Communications in Earth and Environment (in review; 2020b) doi:10.21203/rs.3.rs-39203/v2.de Winter, N., Agterhuis, T. & Ziegler, M. Climate of the Past Discussions 1–52 (2020c) doi:https://doi.org/10.5194/cp-2020-118.Ivany, L. C. The Paleontological Society Papers 18, 133–166 (2012).Schöne, B. R. & Gillikin, D. P. Palaeogeography, Palaeoclimatology, Palaeoecology 373, 1–5 (2013).

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.

The Northeast Atlantic alone has received 1.2 PBq of 14C as liquid and gaseous releases from European nuclear fuel reprocessing plants (NRPs) between the 1950s and present. The input of reprocessing-14C has the potential to elevate the regional 14C content of seawater, sediments and marine biota above the ambient levels expected from the bomb-14C. Yet, a comprehensive assessment of the time evolution of F14C in seawater is still missing for the Northwestern European Seas. Moreover, the least-well studied period of time (1990’s onward) corresponds to the largest liquid 14C releases reported by the Sellafield and La Hague NRPs. In this study, we aim at better constraining the temporal changes of F14C between the late 1960s and 2019, and to delimit the area of influence of reprocessing discharges with regard to 14C. To this end, we combine Accelerator Mass Spectrometry techniques and a novel archive of bivalve shells that inhabited the Irish Sea, the North Sea, Norway and the Bay of Biscay throughout the main period of reprocessing-14C discharge. The shells are made of aragonite, and thus, they can be used as an analogue of the past seawater F14C. The shell-based F14C data can be accurately placed in the temporal context because the animals have a known capture date and short lifespan of two years. The reconstructed F14C values vary between ~1 and ~3 after the 1970s. This range of F14C values is even larger than the one displayed by the atmospheric bomb peak (1 - 1.9). To investigate if the excess 14C is related to the reprocessing releases, we use a simple box model that simulates the seawater F14C by mixing bomb and reprocessing-14C, as well as the naturally occurring 12,14C. In shells from the southern North Sea, the F14C increases 0.1-0.4 above ambient levels after the mid-1990s in response to increased discharge rates of liquid 14C from the La Hague plant. Similarly, the shells collected in the Irish Sea show two consecutive peaks in the mid-1990s (F14C ~ 2.0) and 2000s (F14C ~ 2.2) that can be attributed to peak discharge rates of liquid 14C reported by Sellafield. The F14C in shells from the eastern coast of the UK and Norway are within the range of the ambient values, which indicates the expected rapid dilution of the reprocessing signal with open ocean waters. In previous studies, the bomb-14C marine curve has been used as a benchmark, among others, to estimate the age and growth rate of calcifying animals, to date marine sediments, and to investigate water mass mixing and circulation timescales. Given the biases from the marine bomb-14C curve unraveled by the shell data, we suggest that liquid releases from the NRPs should not be disregarded when applying 14C as a chronological or circulation tool to marine samples collected in the Irish Sea and parts of the North Sea over the last 5 decades.

The interest in Arctica islandica growth biology has recently increased due to the widespread use of its shell as a bioarchive. Although temperature and food availability are considered key factors in its growth, their combined influence has not been studied so far under laboratory conditions. We tested the interactive effect of temperature and food availability on the shell and tissue growth of A. islandica juveniles (9–15 mm in height) in a multi-factorial experiment with four food levels (no food, low, medium, and high) and three different temperatures (3, 8, 13 °C). Shell and tissue growth were observed in all treatments, with significant differences occurring only among food levels (2-way ANOVA; P-value < 0.05). Siphon activity (% open siphons), however, was affected by temperature, food, and the interaction between them (2-way ANOVA; P-value < 0.05). Siphon observations, as indication of feeding activities, played a key role to better understand the growth variation between individuals.

This paper describes the distribution of the razor clam Ensis directus in the Dutch coastal zone with emphasis on its relation to sediment grainsize, in particular silt. The study includes a spatial survey along the coast of North Holland (Netherlands) and an in-situ experiment for the burial of silt. Densities of E. directus appeared highest close to the coast in the siltiest sediment, where also the highest body mass index values (BMI) were found suggesting the best conditions for growth. The largest specimens with the lowest BMI were found at the less silty, outermost off-shore stations. In the shallow (10 m) zone a “lander” frame was deployed at the seabed containing ~ 100 pvc tubes filled with silt free sand that each hosted either a living E. directus , an empty shell, or bare sand. After three 3-weeks periods the silt content in the different tubes was determined and compared. The silt content around a living E. directus appeared 34% (spring) and 12% (autumn) higher than around an empty vertical shell, and 56% (spring) higher than in bare sand. We discuss the different pathways along which silt is brought into subsurface sediment layers and speculate about the potential role of E. directus in the coastal sediment and silt dynamics. It is estimated that E. directus facilitates the (temporal) burial of up to 6 Mton of fine particles in the coastal zone annually. This equals up to 27% of the annual SPM transport along the Dutch coast and is between 45 and 85% of the annual influx into the western Wadden Sea. The results show that the coastal E. directus population has a large impact on mass balance and behaviour of SPM, and on the ecological functioning of Dutch coastal and estuarine ecosystems.

Radiocarbon (14C) is broadly used in oceanography to determine water ages, trace water circulation, and develop sediment- and sclerochronologies. These applications require an accurate knowledge of marine 14C levels, which have been largely perturbed by human activities. Globally during the last century the above-ground nuclear weapon testings have been the primary cause of the increased atmospheric and marine 14C. However, other anthropogenic sources may have caused important regional deviations from the bomb pulse. For the last 70 years European nuclear fuel reprocessing plants have been major contributors of 14C to air and oceans, yet, their regional impact on surrounding marine 14C has been largely overlooked. Here we use a collection of bivalve shells of known capture date and age collected from various locations, including the North Sea, the Irish Sea, Norway, and the Bay of Biscay to reconstruct the sea surface 14C over the last five decades. The measured 14C values for the period 1969–2019, reported in fraction modern, ranged from 1.1 to 1.6 in coastal waters of the Netherlands and from 1.2 to 3.2 along the coast of the UK, indicating significantly higher levels of 14C than those expected for the marine bomb pulse (0.950–1.150). The 14C peaks revealed by the shells coincide with the increase of liquid 14C releases reported from the reprocessing plants of La Hague into the English Channel, and from Sellafield into the Irish Sea. Conversely, the shells from Norway and Spain showed 14C values close to the range of the global marine bomb pulse. The observed large spatial and temporal differences in sea surface 14C show that 14C dating and tracing studies could become problematic in the English Channel, Irish Sea and North Sea for the time period covering the discharge of liquid 14C from the reprocessing plants., Science of The Total Environment, 738, ISSN:0048-9697, ISSN:1879-1026

Marine biogenic materials such as corals, shells, or seaweed have long been recognized as recorders of environmental conditions. Here, the bivalve Cerastoderma edule is used for the first time as a recorder of past seawater contamination with anthropogenic uranium, specifically

Over the past century, the dendrochronology technique of crossdating has been widely used to generate a global network of tree-ring chronologies that serves as a leading indicator of environmental variability and change. Only recently, however, has this same approach been applied to growth increments in calcified structures of bivalves, fish and corals in the world's oceans. As in trees, these crossdated marine chronologies are well replicated, annually resolved and absolutely dated, providing uninterrupted multi-decadal to millennial histories of ocean palaeoclimatic and palaeoecological processes. Moreover, they span an extensive geographical range, multiple trophic levels, habitats and functional types, and can be readily integrated with observational physical or biological records. Increment width is the most commonly measured parameter and reflects growth or productivity, though isotopic and elemental composition capture complementary aspects of environmental variability. As such, crossdated marine chronologies constitute powerful observational templates to establish climate–biology relationships, test hypotheses of ecosystem functioning, conduct multi-proxy reconstructions, provide constraints for numerical climate models, and evaluate the precise timing and nature of ocean–atmosphere interactions. These ‘present–past–future’ perspectives provide new insights into the mechanisms and feedbacks between the atmosphere and marine systems while providing indicators relevant to ecosystem-based approaches of fisheries management.

Marine biogenic materials such as corals, shells, or seaweed have long been recognized as recorders of environmental conditions. Here, the bivalve Cerastoderma edule is used for the first time as a recorder of past seawater contamination with anthropogenic uranium, specifically 236U. Several studies have employed the authorized radioactive releases, including 236U, from nuclear reprocessing plants in La Hague, France, into the English Channel, and Sellafield, England, into the Irish Sea, to trace Atlantic waters and to understand recent climate induced circulation changes in the Arctic Ocean. Anthropogenic 236U has emerged over recent years as a new transient tracer to track these changes, but its application has been challenged owing to paucity of fundamental data on the input (timing and amount) of 236U from Sellafield. Here, we present 236U/238U data from bivalve shells collected close to La Hague and Sellafield from two unique shell collections that allow the reconstruction of the historical 236U contamination of seawater since the 1960s, mostly with bi-annual resolution. The novel archive is first validated by comparison with well-documented 236U discharges from La Hague. Then, shells from the Irish Sea are used to reconstruct the regional 236U contamination. Apart from defining new, observationally based 236U input functions that will allow more precise tracer studies in the Arctic Ocean, we find an unexpected peak of 236U releases to the Irish Sea in the 1970s. Using this peak, we provide evidence for a small, but significant recirculation of Irish Sea water into the English Channel. Tracing the 1970s peak should allow extending 236U tracer studies into the South Atlantic Ocean., Science of The Total Environment, 717, ISSN:0048-9697, ISSN:1879-1026

Long-term and high-resolution environmental proxy data are crucial to contextualize current climate change. The extremely long-lived bivalve, Arctica islandica, , is one of the most widely used paleoclimate archives of the northern Atlantic because of its fine temporal resolution. However, the interpretation of environmental histories from microstructures and elemental impurities of A. islandica, shells is still a challenge. Vital effects (metabolic rate, ontogenetic age, and growth rate) can modify the way in which physiochemical changes of the ambient environment are recorded by the shells. To quantify the degree to which microstructural properties and element incorporation into A. islandica, shells is vitally or/and environmentally affected, A. islandica, specimens were reared for three months under different water temperatures (3, 8 and 13 °C) and food concentrations (low, medium and high). Concentrations of Mg, Sr, Na, and Ba were measured in the newly formed shell portions by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The microstructures of the shells were analyzed by Scanning Electron Microscopy (SEM). Shell growth and condition index of each specimen were calculated at the end of the experimental period.Findings indicate that no significant variation in the morphometric characteristics of the microstructures were formed at different water temperatures or different food concentrations. Shell carbonate that formed at lowest food concentration usually incorporated the highest amounts of Mg, Sr and Ba relative to Ca+2 (except for Na) and was consistent with the slowest shell growth and lowest condition index at the end of the experiment. These results seem to indicate that, under food limitation, the ability of A. islandica, to discriminate element impurities during shell formation decreases. Moreover, all trace element-to calcium ratios were significantly affected by shell growth rate. Therefore, physiological processes seem to dominate the control on element incorporation into A. islandica, shells.

Here we present data on the wax and wane of a subtidal Ensis directus population which settled in 2009 off the coast of Egmond (North Holland Coast in The Netherlands). Initial densities decreased from a maximum of 700 m- 2 in early 2010 to about 50 m- 2 in June 2013. In this period the average length increased from ~ 4 cm to ~ 12 cm. In 2011–2012 the population was sampled at 3 to 6 week intervals and near bottom environmental conditions were monitored continuously. Samples of animals that were collected were used to follow the change in gonadal mass, tissue glycogen content, tissue weight and shell length. On the basis of these data well defined seasonal cycles were observed. The data indicate that the maturation of gonadal tissue already starts early in the year, initially at the expense of somatic tissue. Main spawning takes place in May. After spawning net somatic tissue growth starts after compensation of losses due to spawning. Somatic growth precedes shell growth which starts at water temperatures exceeding 12–14 °C. Mortality, growth and production are comparable to those found for populations in close-by intertidal areas. As such there is no indication that this offshore population significantly suffers from nearby beach nourishments along the Dutch Coast.

Individual age is a key parameter when studying population dynamics of a species. However, accurate age determination in bivalve shells is not always straightforward due to the difficulty of using external growth lines on the shell surface as a reliable method to identify annual growth patterns. In the present paper, we aimed at validating the seasonality in growth lines in the shell of Macoma balthica using stable oxygen and carbon isotopes (delta O-18 and delta C-13) as well as trace elements (Sr, Mn, Mg and Ca).During a 1-year growth experiment, delta O-18 values in the shell carbonate peaked in February/March and matched the annual line visible in the acetate peel of the shell's cross-section. Most carbonate was deposited in the months March to May, which was supported by the observed fast growth in the experiment during this period. Growth stopped between October and December indicating that annual growth lines are formed due to autumn growth stop. Fast growth occurs mainly at temperatures above 6-7 degrees C, although growth may already start at temperatures of about 5 degrees C.delta C-13 profiles did not show any clear seasonality related to the position of the growth lines on the valve or acetate peel and, therefore, cannot be used to estimate age. Along the hinge, Sr was the only element showing variation on the growth lines. High Sr/Ca ratios in the hinge occurred near annual growth lines identified in the acetate peel, suggesting that Sr/Ca ratios may be used to identify annual growth lines and estimate age in M. balthica. Furthermore, counting external lines (on the valve) always lead to an overestimation of age and thus an underestimation of annual growth rates. Therefore, an analysis of the cross-section of the valve seems necessary to accurately estimate age and growth rate in this species. This aspect should be taken into account in studies of growth and population dynamics.

To evaluate the role of the razor clam Ensis directus in Dutch coastal waters, assessment and understanding its population dynamics is important. As such, the age structure of the population forms a key parameter. Accurate age determination in bivalve shells is not always straightforward due to the difficulty of interpreting externally visible growth lines. In the present paper, we aimed at validating the seasonality in growth line formation using visual techniques in combination with stable oxygen and carbon isotope analyses (δ18O and δ13C). High δ18O values in the shell coincided with growth marks on the external surface of the valve and in acetate peels of the shell's cross section. Most shell δ18O samples were assigned to the months June to September. From November to March no samples were retrieved indicating that the shell did not grow. The lowest reconstructed temperature (6.1 °C) suggests that ~6 °C may be the threshold temperature for growth. Nevertheless, most of the reconstructed values fell above 14.5 °C indicating growth occurred mainly in the summer at relatively high temperatures. Shell δ13C profiles followed a more or less seasonal cycle but no direct relationship could be made between δ13C values and annual growth lines. Although counting external annual growth lines led to a correct estimation of age and consequently of growth rates, we recommend analysing acetate peels of cross-sections to support the distinction between annual lines and disturbance lines.

The analysis of 1.8. years of data gives an understanding of the response to varying forcing of suspended particulate matter (SPM) and chlorophyll-a (CHL-a) in a coastal turbidity maximum zone (TMZ). Both temporal and vertical concentration variations in the near-bed layer (0-2. m) in the shallow (11. m deep) coastal zone at 1. km off the Dutch coast are shown. Temporal variations in the concentration of both parameters are found on tidal and seasonal scales, and a marked response to episodic events (e.g. storms). The seasonal cycle in the near-bed CHL-a concentration is determined by the spring bloom. The role of the wave climate as the primary forcing in the SPM seasonal cycle is discussed. The tidal current provides a background signal, generated predominantly by local resuspension and settling and a minor role is for advection in the cross-shore and the alongshore direction. We tested the logarithmic Rouse profile to the vertical profiles of both the SPM and the CHL-a data, with respectively 84% and only 2% success. The resulting large percentage of low Rouse numbers for the SPM profiles suggest a mixed suspension is dominant in the TMZ, i.e. surface SPM concentrations are in the same order of magnitude as near-bed concentrations.

Shells of bivalves potentially provide an excellent archive for high-resolution paleoclimate studies. However, quantification of environmental variables, specifically water temperature remains a very challenging task. Here, we explore the possibility to infer water temperature from changes of microstructural characteristics of shells of the common cockle, Cerastoderma edule . The size and elongation of individual microstructural units, i.e., prisms, in the outer shell layer of seven three to five year-old, specimens collected alive from the intertidal zone of the North Sea near Texel, The Netherlands, and Schillig, Germany, were measured by means of automatic image processing. Growth patterns (circatidal, ciralunidian and fortnightly increments and lines), shell oxygen isotope values and mark-and-recovery experiments were used to place the shell record in a precise temporal context. Irrespective of the locality and ontogenetic age, size and elongation of the prisms increased non-linearly with water temperature. Small (0.12 ± 0.05 μm 2 ) and round prisms (elongation: 2.42 ± 0.31) were formed at temperatures of ca. 10 °C (late April), whereas larger (0.33 ± 0.11 μm 2 ) and more elongated prisms (3.26 ± 0.28) occurred during hot summer (ca. 22 °C). No clear-cut or consistent correlation existed between microstructural characteristics and growth rate as well as a variety of other environmental variables such as salinity, chlorophyll a and turbidity. Based on these findings, a model was constructed from three shells at Texel that enables reconstruction of water temperature with a precision of 1.7 ± 1.0 °C from prism size and elongation: SST = 9.02 + 17.25 P s + 1.10 P e . This model was successfully tested at four shells from Schillig. The new temperature proxy can be of particular interest for paleoclimate studies in nearshore settings when non-recrystallized C. edule shells are available. Future studies are required to verify our findings and check if other species with the same and different microstructures show similar relationships with water temperature.

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

Marine radiocarbon bomb-pulse time histories of annually resolved archives from temperate regions have been underexploited. We present here series of Δ14C excess from known-age annual increments of the long-lived bivalve molluskArctica islandicafrom 4 sites across the coastal North Atlantic (German Bight, North Sea; Troms⊘, north Norway; Siglufjordur, north Icelandic shelf; Grimsey, north Icelandic shelf) combined with published series from Georges Bank and Sable Bank (NW Atlantic) and the Oyster Ground (North Sea). The atmospheric bomb pulse is shown to be a step-function whose response in the marine environment is immediate but of smaller amplitude and which has a longer decay time as a result of the much larger marine carbon reservoir. Attenuation is determined by the regional hydrographic setting of the sites, vertical mixing, processes controlling the isotopic exchange of14C at the air-sea boundary,14C content of the freshwater flux, primary productivity, and the residence time of organic matter in the sediment mixed layer. The inventories form a sequence from high magnitude-early peak (German Bight) to low magnitude-late peak (Grimsey). All series show a rapid response to the increase in atmospheric Δ14C excess but a slow response to the subsequent decline resulting from the succession of rapid isotopic air-sea exchange followed by the more gradual isotopic equilibration in the mixed layer due to the variable marine carbon reservoir and incorporation of organic carbon from the sediment mixed layer. The data constitute calibration scries for the use of the bomb pulse as a high-resolution dating tool in the marine environment and as a tracer of coastal ocean water masses.

Deep-sea benthic communities primarily rely on an allochthonous food source. This may be in the form of phytodetritus or as food falls e.g. sinking carcasses of nekton or debris of marine macrophyte algae. Deep-sea macrourids are the most abundant demersal fish in the deep ocean. Macrourids are generally considered to be the apex predators/scavengers in deep-sea communities. Baited camera experiments and stable isotope analyses have demonstrated that animal carrion derived from the surface waters is an important component in the diets of macrourids; some macrourid stomachs also contained vegetable/plant material e.g. onion peels, oranges, algae. The latter observations led us to the question: is plant material an attractive food source for deep-sea scavenging fish? We simulated a plant food fall using in situ benthic lander systems equipped with a baited time-lapse camera. Abyssal macrourids and cusk-eels were attracted to the bait, both feeding vigorously on the bait, and the majority of the bait was consumed in

In the early 1990’s a conspicuous shift took place in the density of two key macrofauna species at the Frisian Front (SE North Sea). The density of the formerly dominant brittlestar Amphiura filiformis showed tenfold reduction and remained low throughout the observation period (1986–2000). In the same period, the burrowing mud shrimp Callianassa subterranea showed a fourfold increase in density. Since the Frisian Front is a transition area where tidal currents fall just below the erosion threshold of silt and bioturbating mud shrimps can potentially affect the sediment erosion threshold, we examined the effects of the species on sediment erodibility. Two experiments were conducted in laboratory annular flumes. In the first experiment we compared the effects of pre-shift and post-shift combinations of the two species on the erodibility of Frisian Front sediment. The results indicated that the erosion was facilitated by a combination of high densities of C. subterranea and low densities of A. filiformis, representing the situation in the late 1990s. The difference in erodibility was already apparent at velocities equal to the critical near-bed current speed measured at the Frisian Front. In the second experiment the effects of pre- and post-shift densities of A. filiformis on sediment erodibility were compared. This showed that low A. filiformis densities as found in the late 1990’s facilitate erosion, but the effect is only significant at velocities above the critical near-bed velocity in the field. At the latter velocity, no significant difference in erodibility was found between the two A. filiformis densities. This implies that the difference in turbidity in the first experiment was mainly due to the activity of C. subterranea. The experimental results indicate that resuspension at the Frisian Front may occur more frequently as a result of the shift towards a Callianassa dominated community. More frequent resuspension of bottom sediment, most likely amplified by the climate induced increase of wind strength in the North Sea, may hamper the recovery of the A. filiformis adult population.

In October 2001, we observed a deep-ocean phytodetritus deposition event on Chatham Rise beneath the Subtropical Front (STF). The origin of this phytodetritus was probably an extensive phytoplankton bloom that occurred in the STF in the preceding weeks. We assessed the spatial distribution of the deposition event using video images from benthic lander and epibenthic trawl deployments and sediment pigment analyses at six sites on a north–south transect across Chatham Rise. High surficial sediment chlorophyll a concentrations were restricted spatially to the southern flank of Chatham Rise (350–1,200-m depth) with the highest values centered at ,750-m water depth (750 S). This southern 750 S site was also the only site where macroscopic phytodetritus was observed, coincident with elevated benthic biomass and sediment community respiration rates. At 750 S, phytodetritus resuspension was observed on video and corroborated by current meter, sediment trap, and optical

From boxcore and dredge samples taken along a depth transect across the Faroe Shetland Channel (FSC) in 1997 and 1999, molluscs were sorted and identified. On the basis of their numerical abundance, the stations could be clustered into three groups, reflecting the depth extension of the main water masses in the FSC. Between 400 and 500 m depth, both the number of taxa per sample and the number of specimens, were highest. Bivalves were mainly caught by the boxcorer and the dredge was best suited to collect the epifaunal gastropods. According to the literature, at mid-slope depths, resuspension is increased by the action of internal waves, which leads to the development of intermediate nepheloid layers. This increased concentration of suspended matter may serve as a food source of low quality. Likewise the low amounts of suspended matter with a relatively high quality of particulate organic matter, such as from ∼400 and ∼700 m may act similarly and explain the relative high abundance of filter feed...

Internal growth lines in shells of 3 suspension-feeding bivalves (Arctica islandica, Mya truncata and Chamelea striatula) from the SE North Sea were analysed in search of common inter- annual variations of their growth rate. The high similarity (69 to 80%) between the growth records in the 3 species suggests that a large-scale (climatic) factor is responsible for an important part of the variation in annual shell growth. The common trend extracted from the individual growth records was correlated with monthly data on phytocolour, NAO index, temperature and wind. The strength and sign of the effect of the last 3 factors varied seasonally. Effects of wind strength and direction were analysed in detail, as in situ measurements showed that wind speeds >10 m s -1 (Beaufort 6) cause resuspension of fine sediment at the site where the bivalves were collected. Resuspended sed- iment causes a drop in the quality of food for suspension feeders. During the bivalve growing season, northwesterly to easterly winds tended to depress growth, whereas winds with a westerly component mainly had a positive effect. Strong winds from a WNW direction in May, however, had a negative effect and could explain the highest proportion of variance in the common growth trend; WNW winds have a long fetch at the study area and generate (high) long waves, facilitating resuspension of fine sediment at relatively low wind speeds.

The bivalve mollusc Arctica islandica is an important commercial species with a presumed panmictic dispersal strategy, and is widely distributed throughout much of the soft sediment benthos of the North Atlantic continental shelf. Previous studies have shown that there can be gross morphologi- cal differences between populations, which has led to the suggestion that this may be reflected in geno- type. So far, only one study has examined the population genetics of this species, revealing, depending upon location, that populations are only genetically distinct at a macroscale (>1000 km), thereby supporting the assumption of panmixia. Examination of the quantitative morphological traits between 5 different populations (4 North Sea and 1 Canadian) determined that all populations could be readily identified from their unique morphologies (shapes/growth patterns) derived from 2 factors resulting from a principal components analysis. Investigation, using random amplified polymorphic DNA (RAPD) analysis, into the genetics of the populations, to indirectly assess whether the observed phenotypic differences could be related to potential differences in genotype, revealed that all populations were genetically distinct (between populations overall phiST = 0.662) from each other even at a microscale (< 25 km) (phiST = 0.719). However, no correlation between genetic distance, morphological distance and/or geographical distance, whatever metric was applied, could be obtained. It is concluded that although phenotypic differences can be used to distinguish between populations of A. islandica, it should not and cannot be used to infer genetic differences in the absence of further studies. What is interesting is that the results from the genetic analysis dispute the presumption that the dispersal patterns of A. islandica is in any shape or form panmictic. This has very important consequences for the management of the species. The results are discussed with reference to the possible mechanisms responsible for maintaining a high degree of genetic diversity between the populations that were studied.

Megafauna biomass and feeding guilds were studied on the NW Iberian upwelling Continental Margin in order to determine the presence of enriched zones pointing to enhanced particle input. We compare these findings with similar data obtained from a transect across the Celtic Continental Margin that represents a regime without coastal upwelling. Additionally sediment concentrations of phytopigments (chlorophyll-a, phaeophorbides) representing recent inputs of algal production and of nucleic acids (DNA, RNA) are used as proxies for microbial biomass, to assess if there was a relation between these parameters and the megafauna distribution. The sediment on the upper slope (

To study the effects of increased near-bottom turbulence, individuals ofAstarte sulcata (Bivalvia) were collected along a depth gradient in the Faroe-Shetland Channel during a research cruise in April 1999. These bivalves were found at depths ranging from 250 m to 800 m. We analysed their long-term growth by means of counting growth lines in the hinge. The average shell size differed at the different depths. The largest animals were found at 300 m (average: 22–23 mm) and the smallest ones at 600 m (average: 15–16 mm). A trend was also found in the age structure at 250 m to 350 m depth.Astarte at 250 m possessed on average 45 growth lines compared to an average of 69 lines in animals obtained from 350 m depth. It was impossible to determine the relative age ofAstarte from 500 m, 600 m and 800 m depth because they did not have clearly defined growth lines. The above-mentioned differences in size, age and growth line visibility are discussed in the light of the effects of temperature and internal waves. Interestingly, unlike other large filter feeders,Astarte appears to be negatively affected by internal wave action.

In the present study we estimated differences in shell growth rates ofChamelea gallina (Linnaeus), from relatively food poor areas with growth rates from specimens collected from a frontal area, which has been regarded as highly productive. The results have been compared with growth rates obtained for two other benthic interface feedersArctica islandica (Linnaeus) andEchinocardium cordatum (Pennant) from the same geographical area.

Within the framework of the EU-funded BENGAL programme, the effects of seasonality on biogenic silica early diagenesis have been studied at the Porcupine Abyssal Plain (PAP), an abyssal locality located in the northeast Atlantic Ocean. Nine cruises were carried out between August 1996 and August 1998. Silicic acid (DSi) increased downward from 46.2 to 213 μM (mean of 27 profiles). Biogenic silica (BSi) decreased from ca. 2% near the sediment–water interface to

The impact of seasonal pulses of phytodetritus on the grazing behaviour of Oneirophanta mutabilis was assessed on the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Sediment and sediment trap samples were analysed by HPLC to estimate the quantity and quality of the organic material in terms of phytopigments and nucleic acids. Food selection by Oneirophanta was estimated by analysing these constituents in the gut contents. The study area is characterised by large interannual variations in the deposition of fresh organic material. The mass fluxes at 10 m above bottom (mab) varied from 0.25 g DW m −2 d −1 in September 1996 to −2 d −1 in March 1997. The material caught in the sediment trap in September 1996 had a relative fresh signature with a chlorophyll -a :phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) the chlorophyll -a :phaeophorbide ratio remained low. In sediment cores this ratio showed a similar seasonal and inter-annual pattern, and again September 1996 was the period of maximum abundance of fresh organic material in the surficial sediment. The analyses of the gut contents of Oneirophanta mirrored exactly the seasonal variation of the phytopigments in both the sediment and the sediment trap material. Concentrations of pigments in the fore-gut were 5 to 15 times higher than in the sediment and the nucleic acid concentrations were up to 80 times higher. This discrepancy between pigments and nucleic acids concentrations suggests that the latter are “indigenous” to the gut of Oneirophanta , either because the gut contains high numbers of actively-dividing bacteria or as a result of cell lysis of the gut epithelium. The seasonal differences in the pigment concentration factor suggest that Oneirophanta does not actively search for hotspots where pigment concentrations are enriched. By using the degradation rate of chlorophyll- a in the PAP sediments, the minimum residence time of chlorophyll in the sediment within the gut of Oneirophanta was calculated. In combination with gut volume and density data it was estimated that each year the Oneirophanta population skims a third of the sediment surface at the PAP site.

We have assessed the impact of seasonal pulses of phyto-detritus towards the bottom of the Porcupine Abyssal Plain (PAP) in the NE Atlantic. Phytopigments were determined (HPLC) in sediment, near-bottom suspended matter and sediment trap samples to obtain an impression of the quantity and quality of the organic material reaching the bottom. Its supposed effect on the benthic community was estimated on the basis of in situ Sediment Community Oxygen Consumption (SCOC) rates, deck oxygen micro profiles as well as chlorophyll mixing and degradation rates. There was considerable interannual variation in the deposition of fresh organic material. In September 1996 the mass flux at 10 m above the bottom was 0.25 g DW m −2 d −1 . The material caught in the trap was relatively fresh with a chlorophyll-a : phaeophorbide ratio of 1.33. During the other seasons (March 1997, July 1997 and October 1997) such fresh material was absent and even in July, the period in which fresh material is supposed to have arrived on the bottom, the ratio remained low, viz. 0.23. Based on these findings we conclude that in 1997 only small amounts of already degraded material arrived at the sea floor. On the basis of the large quantities of fresh material found in September 1996, the existence and subsequent deposition of autumn blooms should be considered. With in situ respirometry no effect of the differential quality and quantity of the settling detritus could be detected, whereas model parameters based on oxygen microprofiles demonstrated changes associated with the supposed seasonal cycle. Also the downcore pigment distribution of chlorophyll-a and derived mixing and degradation coefficients showed variations which were linked to the observed seasonal changes in input of organic matter.

The growth lines in shells of Arctica islandica from the Fladen Ground have been used to construct long-term chronologies of growth variations. Individual specimens showed characteristic sequences of periods in high and low growth rates. Because the deviations were strongly synchronized, an environmental factor is held responsible. Inter-annual variations in either temperature or phytoplankton abundance could not explain the observed variations. The hypothesis is therefore put forward that the occurrence of dense patches of Arctica and the variations in growth result from variations in import and accumulation of organic matter by an eddy system overlying the area. Evidence for this hypothesis is provided by the correlation between the estimated inter-annual influx of Atlantic water into the North Sea and the observed growth variations.