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We evaluated the prevalence of influenza A virus (IAV) in different species of bivalves inhabiting natural water bodies in waterfowl habitat along the Delmarva Peninsula and Chesapeake Bay in eastern Maryland. Bivalve tissue from clam and mussel specimens (Macoma balthica, Macoma phenax, Mulinia sp., Rangia cuneata, Mya arenaria, Guekensia demissa, and an undetermined mussel species) from five collection sites was analyzed for the presence of type A influenza virus by qPCR targeting the matrix gene. Of the 300 tissue samples analyzed, 13 samples (4.3%) tested positive for presence of influenza virus A matrix gene. To our knowledge, this is the first report of detection of IAV in the tissue of any bivalve mollusk from a natural water body.

The relative influence of consumers (top down) and resources (bottom up) on the distribution and abundance of organisms remains a key question in ecology. We examined the relationships between consumer and resource variables along a productivity gradient for a dominant predator–prey interaction in a marine soft‐sediment system. We 1) quantified density and size of the clam Macoma balthica (prey species) in six replicate sites at each of four habitat types (shallow mud, deep mud, muddy sand and detrital mud) in the Rhode River, Chesapeake Bay. We selected one habitat type of high food availability and clam density (shallow mud) and another of low food availability and clam density (muddy sand) for manipulative experiments. Then, we 2) measured M. balthica survival and growth through transplants, 3) measured food availability as sedimentary organic carbon content, 4) quantified predator density, and 5) calculated predator foraging efficiency in the two habitat types. Clam density in the four habitat types differed and was related to sedimentary carbon availability and predator density. One of the habitats, detrital mud, appeared to be a population sink because it only held juvenile Macoma that never survived to reproductive age. Macoma size and growth, and predator (mainly blue crab Callinectes sapidus) densities were positively correlated with productivity and were higher in shallow mud than muddy sand. In contrast, Macoma mortality, local ‘interaction strength’, and predator foraging efficiency were lower in the productive habitat (shallow mud). Thus, predation intensity was inversely correlated with productivity (food availability); consumer and resource effects differed by habitat type; and, at a relatively small spatial scale, consumer and resource forces jointly determined population dynamics in this soft‐sediment marine system.

A laboratory microcosm experiment was performed to study the effect of bivalves on meiobenthic and nematode community structures. Three bivalve species dominant in shallow coastal sediments of the southern Baltic Sea differing in terms of feeding mode, faecal deposition and sediment depth penetration (Macoma balthica, Cerastoderma glaucum and Mya arenaria) were selected as model organisms: our experiment demonstrated that although the bivalves had no overall effect on total meiobenthic densities, they variously affected a number of meiobenthic major taxa. Species buried under the sediment surface (M. balthica, M. arenaria) facilitated meiobenthos to penetrate deeper sediment layers compared to the surface-dwelling bivalves (C. glaucum). The most conspicuous response of meiobenthos and nematodes to bivalve activities was, however, observed at the sediment surface: densities of juvenile bivalves and rotifers, and the dominant nematode species (Adoncholaimus thalassophygas, Desmolaimus cf. zeelandicus and Halomonhystera disjuncta) were significantly reduced in surface sediments in Macoma microcosms compared to other treatments. It is suggested that different bivalve feeding modes (deposit-feeding vs. suspension-feeding), attributes of faecal deposition (to the sediment surface vs. to subsurface sediments) and depth of sediment penetration can significantly change meiobenthic and nematode communities in sandy sediments.

Many size-selective predators switch their diet during ontogeny. At the White Sea, the adult moonsnails Amauropsis islandica feed mostly on Macoma balthica clams. The diet of juveniles was largely unknown. We conducted a field survey and a caging experiment to find out if juvenile moonsnails can prey on Hydrobia ulvae, and whether they prefer this snail to their usual prey. Live molluscs and their intact or perforated shells were collected from 34 sediment cores. We exposed the single-prey cages with 50 Macoma (MP) or 50 Hydrobia (HP) together with five Amauropsis juveniles, as well as the cages where both prey species were in a 25:25 proportion (HMP). While live Hydrobia was more abundant in the natural assemblages, Amauropsis preferred Macoma, as indicated by proportions of perforated shells. The caging experiment produced similar results. Per capita Macoma consumption rate was significantly higher than Hydrobia consumption rate (6.4 ± 0.5 mg day−1 ind.−1vs. 1.4±0.2 mg day−1 ind.−1 in MP and HP respectively). Prey consumption rates in the single-prey treatments were higher than in mixed-prey cages regardless of prey species. Different mechanisms explain this variation: for Hydrobia it is a consequence of the dietary shift, while for Macoma it reflects the ‘floor’ effect in HMP cages, where virtually all Macoma had been drilled by the end of exposure term. While Macoma is the preferable prey of young Amauropsis, Hydrobia can supplement the diet of juveniles when Macoma is scarce in certain locations.

Long-term (>40 yr, started in the 1970s) data series of Limecola (Macoma) balthica dynamics in 4 distant (>100 km) areas of the Dutch Wadden Sea are described and compared, including annual recruitment, total abundance, age composition (recruits/adults) and adult survival. The aim was to determine to what extent long-term changes in L. balthica population attributes were synchronous in populations throughout the Dutch Wadden Sea and to identify possible underlying causes. At all 4 sites studied, changes in annual recruitment (n m-2 of spat-sized animals in summer) was synchronous with long-term declining trends and peaks and lows occurring in the same years at all sites. Adult survival was high for the first 15 to 20 yr, but irregular after 1990 with low values for periods of varying length. In contrast to the strongly synchronized recruitment, the low-survival periods were not synchronous over the Wadden Sea. Adult density and total biomass varied in parallel over most sites and were low throughout the Dutch Wadden Sea (less than a quarter of the earlier long-term average) from 2005 onwards. The factors suggested to underlie these changes in abundance were (1) negative effects of climate warming on recruitment, which includes higher abundance of predators on young bottom stages, and (2) an unknown cause of enhanced adult mortality, possibly disease. Synchronization in recruitment, adult density and total biomass of L. balthica populations throughout the Dutch Wadden Sea indicates that they are part of a Wadden Sea-wide metapopulation.

We followed the dynamics of the population of the bivalve Limecola (Macoma) balthica in the westernmost part of the Wadden Sea by monitoring for 44 years (1973–2016) its numbers and age composition at 15 sites in a 50-km2 tidal-flat area. During the first half of this period, the annual recruitment and adult survival were at a relatively constant level, resulting in rather constant numbers. During the second half of the observation period, annual recruitment and adult survival showed declining trends, resulting in seriously reduced adult abundance. Sudden substantial reductions in adult survival started around 1996 at a few sites to spread over the entire area within 5 years, like an infectious disease. The resulting small adult stocks produced small numbers of recruits. The stock–recruitment curve showed an increasing part up to about 30 adults m−2, followed by invariably successful recruitments at > 40 adults m−2. Both recruitment and adult survival were negatively related to water temperatures. However, elevated temperatures after 1997 could not explain the very low survival rates observed after 1996 and the very low recruitment success after 2003. So far, recovery of the population has hardly taken place, with both recruitment and adult survival at lower levels than observed for the initial stable period.

In this study, we describe food availability and diet selection of the Red Knot Calidris canutus islandica wintering in three estuarine bays on the French Channel coast. We examined whether the distribution of birds is related to the density and availability of high quality prey. Results indicate strong seasonal and inter-annual variation in the abundance of birds and considerable variation in prey-item abundance and diet selection depending upon site. At Mont Saint-Michel Bay, the prey community was dominated by Baltic Tellins, Macoma balthica. As expected from their high meat-to-shell ratio, Macoma contributed more than 90% of the diet. Most of the cockles, Cerastoderma edule were too large and their quality too low to be preyed upon. Less than 100 km away, in Saint-Brieuc Bay, Red Knots mainly selected the Thin Tellin Tellina tenuis. Although Tellina are a lower quality prey than Macoma, they occurred at a high density and in some winters might explain why the number of Red Knots exceeds those at Mont ...

Behavior has a predictive power that is often underutilized as a tool for signaling ecological change. The burrowing behavior of the deposit feeding bivalve Macoma balthica reflects a typical food-safety trade-off. The choice to live close to the sediment surface comes at a risk of predation and is a decision made when predation danger, food intake rates or future fitness prospects are low. In parts of the Dutch Wadden Sea, Macoma populations declined by 90% in the late 1990s, in parallel with large-scale mechanical cockle-dredging activities. During this decline, the burrowing depth of Macoma became shallow and was correlated with the population decline in the following year, indicating that it forecasted population change. Recently, there has been a series of large recruitment events in Macoma. According to the food-safety trade-off, we expected that Macoma should now live deeper, and have a higher body condition in association with this change in depth of living. Indeed, we observed that Macoma now lives deeper and that living depth in a given year forecasted population growth to the next year, especially in individuals larger than 14 mm. As living depth and body condition were strongly correlated in individuals larger than 14 mm, larger Macoma could be living deeper to protect their reproductive assets. Our results confirmed that burrowing depth signals impending population change and, together with body condition, can provide an early warning signal of ecological change. We suggest that population recovery is being driven by improved intertidal habitat quality in the Dutch Wadden Sea, rather than by the proposed climate-change related effects. This shift in ecosystem state is suggested to include the recovery of diatom habitat in the top layer of the sediment after cockle-dredging ended.

The first occurrence and presence of the bivalve Macoma balthica in the Pleistocene shallow marine sediments (Crags) of East Anglia has long been used to characterise the youngest “Weybourne” or “Wroxham” Crag Formation of Early to early Middle Pleistocene age. A review of recent work on the morphological variation and genetic lineages of living populations of the species and of work on fossil discoveries in East Greenland suggests that the current palaeontological species definition is too narrow, that the species arrived in the Atlantic about 2.4 Ma and much earlier than is envisaged from the studies of the North Sea Basin, and that there were several trans-Arctic migrations of the species during the Pleistocene. This paper reviews these findings and concludes that: (i) detailed morphometric analyses of fossil Macoma species from the Crag need to be undertaken and the species definitions comprehensively reviewed to take account of the morphological and genetic variation seen in modern populations; (ii) detailed morphometric analysis of modern M. balthica should be undertaken and tied to the different genetic lineages, and (iii) the current palaeontological definition of Macoma balthica should not be relied on as the basis for a First Appearance Datum (FAD) in the Southern North Sea basin.

Recent reductions in sea ice cover and thickness in the Arctic will lead to changes in food supplies for benthic consumers. We experimentally assessed responses of two common Arctic macrobenthic species, Macoma balthica (Bivalvia) and Monoporeia affinis (Crustacea) from Kotzebue Sound (Alaska, USA) to varying food materials (phytoplankton and ice algae). Phytoplankton and 13C-labelled ice algae were added separately or together to pre-sieved sediment cores containing known numbers of Macoma or Monoporeia. After 8 d, sediments and animals were analyzed for bulk C/N contents, isotopic signatures, fatty acid compositions and compound-specific δ13C values. Our results showed that the two species responded differently to varying food materials. Loss of characteristic fatty acids and changes in δ13C values in the surrounding sediments indicate that Macoma preferentially consumed ice algae compared to phytoplankton, while Monoporeia non-selectively ingested both food materials. Feeding behaviors also differed between the two species: Macoma fed primarily on material from the sediment surface, and did not appear to mix material to depth, while Monoporeia mixed some fresh food material from the surface down to subsurface sediments (1–2 cm). Analysis of animal biomass showed more 13C-labelled organic carbon from ice algae was assimilated by individual Macoma compared to individual Monoporeia. Moreover, δ13C values of fatty acids in Macoma were much higher than those in Monoporeia, suggesting that Macoma directly assimilates fatty acids from their food source while Monoporeia might de novo biosynthesize fatty acids in their biomass. Additionally, both species had higher fatty acid contents and proportion of polyunsaturated components when they fed on ice algae compared to phytoplankton, implying that ice algae may be a better food than phytoplankton for Arctic benthos. Finally, analysis of bacteria-specific fatty acids in sediments (from both types of animal cores) showed that the δ13C values were enriched up to 400‰ relative to natural background values (−25% to −30‰), suggesting that organic carbon from fresh ice algae could be rapidly incorporated into bacteria biomass. The collective results of this experimental study suggest that the changes in food supplies due to reduction of ice coverage will have a greater impact on those benthic organisms that prefer ice algae to phytoplankton. This may lead to the potential changes in community structure favoring those organisms that can best utilize the fatty acids contained in both phytoplankton and ice algae.

We studied the effect of crustacean predators on native/non-native Macoma balthica bivalves in aquarium experiments. North Sea M. balthica (NS Macoma) were recently observed in the southern Baltic Sea. They differ genetically and in terms of morphology, behaviour and evolution- ary history from Baltic Sea M. balthica (BS Macoma), and this may affect predation pressure and community structure. We hypothesised that predators consume more of the prey they co-exist with. NS Macoma and BS Macoma were exposed to crustacean predators common in the North Sea (Carci- nus maenas and Crangon crangon) and in the Baltic Sea (C. crangon and Saduria entomon). Contrary to our hypotheses, the North Sea predators ate more BS Macoma, and S. entomon ate more NS Macoma. The crush-limited C. maenas preyed more on globular BS Macoma, whereas S. entomon, which do not crush but pry open the bivalve shell, ate more NS Macoma, which have a lighter (thus probably thinner) shell than BS Macoma. When NS and BS Macoma were offered together, BS Cran- gon ate more NS Macoma. We also studied BS Crangon consumption of M. balthica to assess whether sizes offered fall within the size spectrum that C. crangon can eat. Small (20 to 40 mm long), medium (40 to 50 mm) and large (50 to 60 mm) C. crangon especially ate small M. balthica. Differences in shape, size and meat/shell weight ratio between the BS and NS Macoma partly explained the differences in the susceptibility to predation by native and non-native predators.

A main molecular subdivision in the circumpolar Macoma balthica complex has been described between Atlantic and Pacific taxa. In NE Europe, the clams of the White and Barents Seas, however, show deviant genetic structures. Using allozyme and mitochondrial DNA data, we explore the hypothesis that these deviations result from hybridization between an Atlantic (M. b. rubra) and an invading Pacific (M. b. balthica) lineage. A practically pure Atlantic Macoma extends from France north to the Varanger Peninsula (NE Norway), whereas populations farther east have genetic compositions intermediate between true Atlantic and true Pacific. Admixture estimates range from 32 to 90% Pacific contribution, with a notable deviation in a nearly pure Atlantic outpost in the Mezen Bay (NE White Sea). The pattern of variation is not one of a simple collinear mixing however. Different characters exhibit different degrees of introgression, and the relative introgression varies regionally. Yet, there are practically no interlocus genotypic disequilibria between the diverged loci, which brings out the White Sea-Barents Sea M. balthica as the best-documented marine animal hybrid swarms so far, arisen through amalgamation of genomes previously isolated since pre-Pleistocene times. On top of the main admixture pattern, strong geographical structuring is also seen in characters unrelated to the principal systematic distinction. The persistence of the regional patterns indicates restricted gene flow at the present time, despite the high dispersal potential of the species. The causes of this structuring could be in a complex history of colonization events and features of local hydrography enhancing isolation and divergence of populations.

Ecosystem engineers can influence community and ecosystem dynamics by controlling resources, modifying the flow of energy or biomass, or changing physical characteristics of the habitat. Invasive hybrid cordgrass ( Spartina alterniflora × Spartina foliosa ) is an ecosystem engineer in salt marshes in San Francisco Bay, California, U.S.A. that raises intertidal elevations and may be either increasing C 4 plant carbon input into food webs or tying up carbon in a form that is not usable by consumers. A manipulative experiment compared abundance, growth, and stable isotope (δ 13 C and δ 15 N) composition of the clam Macoma petalum (= M. balthica ) among native marsh, hybrid Spartina , and mudflats in central San Francisco Bay. We found higher densities (individuals m −2 ) of M. petalum on mudflats compared to either native or hybrid Spartina ( p Macoma petalum shell growth was significantly greater in mudflats than in either vegetation type in 2002 ( p = 0.005) but not 2003. Differences in shell growth between native and hybrid Spartina were not significant. Stable isotope results showed differences between habitats in δ 13 C but not δ 15 N. Carbon signatures of M. petalum placed in Spartina were much more depleted than the isotopic signature of Spartina . Neither native nor hybrid Spartina appears to be a significant carbon source for M. petalum in San Francisco Bay, and we found no evidence that hybrid Spartina contributes carbon to M. petalum beyond what is provided by S. foliosa , despite the hybrid's much greater biomass. Our results show that loss of mudflat habitat, rather than increased input of C 4 carbon, is the greatest effect of the invasion of hybrid Spartina on M. petalum .

We report the application of a recently developed molecular method, single step nested multiplex PCR (SSVM-PCR) assay and microscopy to identify and investigate temporal patterns of bivalve larvae in a Danish estuary, Isefjord. All samples were collected during the SUSTAINEX program from June to November 2001. Using the molecular assay, larvae could be categorized into six groups: the blue mussel, Mytilus edulis, Ensis spp., species of the Myoidae superfamily (Mya spp.), the common cockle (Cardiidae family), members of the Abra and Macoma genera of the Tellinoidae superfamily and members of the surf clam genera, Spisula spp. A seventh group was composed of unknown larvae. Greater resolution was possible by microscopy, but only for relatively large and intact individuals (>150-200 μm). The molecular approach was capable of differentiating between larvae regardless of shell size. Where it was possible to directly compare identifications based on both methods, concordance was high for M. edulis, Macoma balthica/Abra alba and E. americanus, whereas identification of Myoidae spp. and Cardiids was less consistent. Over the course of the study, two patterns of larval occurrence were observed. Larvae from species known to exhibit a protracted annual spawning period (M. edulis, Myoidae spp., Mysella bidentata and Cardiids) were present in the water column throughout the sampling period, whereas larvae of Abra alba, Barnea candida, E. americanus, Macoma balthica, Musculus marmoratus Scrobicularia plana and Tapes pullastra appeared at clearly defined periods.

Patterns of nine intracellular free amino acids (FAA), which are utilized as organic osmolytes for salinity-induced cell volume regulation in marine osmoconformers, were compared in five Macoma balthica populations and seven Mytilus spp. populations along their European distribution. Three types of FAA patterns were classified within both taxa: a northern Baltic type, a southern Baltic type and an Atlantic/Mediterranean type which mainly differ regarding the share of alanine and taurine. Differences are discussed in relation to habitat salinity and population genetics. Along a salinity gradient, the total size of the intracellular FAA pool did not differ between sympatric M. balthica and Mytilus spp., and was significantly correlated with habitat osmolality in a range from 70 to 600 mmol kg−1 H2O (oligohaline to mesohaline) in both bivalves. In M. balthica, this correlation was mainly based on significant correlations of alanine (15–100 mmol kg−1 DW), glycine (30–100 mmol kg−1 DW) and taurine (0–70 mmol kg−1 DW) with habitat osmolality. In Mytilus spp., only glycine (25–100 mmol kg−1 DW) and taurine (4–180 mmol kg−1 DW) were significantly correlated with habitat osmolality. The concentration of alanine was three times lower in Mytilus spp. than in M. balthica and did not correlate with habitat osmolality. Within a habitat osmolality range from 600 to 1,100 mmol kg−1 H2O (mesohaline to marine) the concentration of FAA remained constant in both taxa. It is suggested that under marine conditions additional organic osmolytes must become more important for cell volume regulation in Macoma and Mytilus.

Variation in habitat quality and resource availability can affect the distribution and growth of animals. Thin-shelled clams dominate many benthic communities in Chesapeake Bay, both in numbers and in biomass, and they can comprise up to 50% of the blue crab (Callinectes sapidus) diet. Our objective was to determine which habitats were optimal for juvenile crab growth and how growth related to food availability. We experimentally examined benthic infaunal food availability (primarily bivalves) and concurrent growth of juvenile blue crabs at 30–40 sites along 50 km of the York River during fall 2000 and spring 2001. Each year, 4–10 replicate sites along the York River were established in each of five habitats: (1) Seagrass, (2) Mud at the river mouth, (3) Sand at the river mouth, (4) Mud upriver, and (5) Sand upriver. Food availability inside and outside of 0.43-m2 crab growth cages was examined, along with crab growth after 3–6 months inside cages. In both years, after 3–6 months, the Baltic clam, Macoma balthica, was abundant inside and outside the cages, whereas the soft-shell clam, Mya arenaria, was only abundant inside cages. Densities of Macoma were greatest in upriver mud and sand, while those of Mya were greatest in upriver sand. Crab growth was significantly greater in spring-summer than fall-winter and was significantly higher in upriver mud and sand, where clam densities were highest, than at the river mouth. The upriver region was near the turbidity maximum, which may enhance pelagic and benthic productivity and thereby provide more food for clams and therefore for blue crabs. Crab growth in seagrass was intermediate between that upriver and at the mouth, suggesting that upriver, unvegetated, subtidal habitats adjacent to salt marshes serve as valuable nursery habitats rivaling seagrass beds.

We report results of a laboratory experiment that examines the effect of density-dependent interactions among infauna on organism–sediment–seawater relationships. The experiment includes a time series documentation of feeding behavior of the deposit- and suspension-feeding bivalve Macoma balthica , concurrent with measures of sediment biogeochemical processes that are affected by different feeding modes. We hypothesized that feeding behavior and emigration rates might shift with increasing density, and that these shifts would have cascading effects on benthic primary productivity, sediment–seawater exchanges, and porewater concentrations of ammonium and silicate. Macoma individuals were maintained in aquaria at three different densities (46, 230, and 460 individuals m −2 ) that fall within their natural abundances in the Chesapeake Bay. Individuals fed mostly on suspended material throughout the experiment, resorting to deposit feeding behavior only at the highest densities. Disturbances on the sediment surface during deposit feeding periods were not sufficient to impact benthic primary productivity and the associated interception effect of microalgae on sediment–seawater exchanges, as seen in previous studies. However, the bivalves impacted sediment fluxes directly through bioturbational activity, and these effects showed significant density interactions. For ammonium, fluxes ranged from 1.3 to 3.7 mmol m −2 d −1 and generally did not increase as a function of increasing Macoma density. Rather, highest fluxes generally were observed in intermediate density treatments. For silicate, a different trend was observed. Fluxes tended to parallel density, and ranged from 6.4 to 13.5 mmol m −2 d −1 , however, the relationship was not linear. These observations suggest that as infaunal density shifts, so does the balance of ammonium to silicate efflux. Thus, benthic population structure may impact water column processes not only through enhancing the flux, but also through alteration of elemental ratios. Experiments that uncover the strength of these interactions, and models that blend the actions of individuals, populations, and material components, would greatly enhance our understanding of the geochemistry of organism–sediment relations.

During the first winter of their life, large numbers of the tellinid bivalve Macoma bal- thica (L.) migrate from their first-summer coastal nurseries on high tidal flats in the Wadden Sea to areas further offshore, including low tidal flats and subtidal areas in the Wadden Sea and adjacent parts of the North Sea. In the western part of the Dutch Wadden Sea, we compared M. balthica redis- tribution in cold and mild winters during the 29 years from 1973 to 2002 to find out whether migra- tion activity was related to winter character. Migration occurred on a larger scale in cold winters than in mild winters, with larger decreases in density of coastal populations and larger increases in den- sity of offshore populations following a cold winter than following a mild winter. In subtidal areas, such secondary recruitment, at an age of almost 1 yr, was higher than primary recruitment through post-larval settlement. In subtidal areas, M. balthica year-classes were particularly strong when their first winter had been cold and when primary first-summer recruitment had been abundant in nearby coastal tidal-flat areas.

Sediments in Sydney Harbour, Nova Scotia, are highly contaminated by polynuclear aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and heavy metals. Histopathologic and histochemical evaluations were made on the Baltic clam, Macoma balthica, exposed to 11 Sydney Harbour sediment samples. Histologic lesions in digestive gland (tubular dilation or atrophy, macrophage aggregates, tubular cell necrosis, and tissue inflammation) and gonads (macrophage aggregates, supporting cell, germ cell, and ovarian cell necroses) were frequently detected in clams exposed to the most contaminated sediments from the harbor. Clams exposed to these contaminated sediments also had the highest acid phosphatase activity. The average scores of tubular dilation or atrophy, ovarian cell necrosis, and the sums of mean digestive gland lesions correlated significantly with sediment PCBs, and the activities of acid phosphatase correlated significantly with sediment heavy metals, PAHs, and PCBs. Among the lesions, digestive gland tubular dilation or atrophy, tubular cell, germ cell, and ovarian cell necroses, and the activity of acid phosphatase are the best sublethal effect indicators in Macoma exposed to Sydney Harbour sediments. Key words: biomarkers, chronic biologic effects, clams, histology, histochemistry, Macoma balthica, marine sediment, polynuclear aromatic hydrocarbons, polychlorinated biphenyls.

Juveniles of the bivalve Macoma balthica live on tidal flats in the Wadden Sea. This study examined the interaction of Macoma with the infaunal polychaetes Arenicola marina and Nereis diversicolor and the gastropod Retusa obtusa. The distribution of M. balthica spat on the flats, shortly after settlement in April, showed a positive correlation with the Arenicola distribution and a negative correlation with Nereis distribution. There were no locations where Macoma spat and Retusa occurred together. In August, Macoma spat had grown too large for predation by intertidal infauna. Small individuals of Macoma spat were found in stomachs of Arenicola (0.14 worm 1 ) and Nereis (0.05 worm 1 ). Laboratory experiments showed that Nereis and Retusa could reduce Macoma spat abundance, both in the absence and presence of sediment and alternative prey. Arenicola reduced the abundance of small Macoma (

As a characteristic buried tellinid bivalve, Macoma balthica has a long inhalent siphon that enables it to feed in two different ways: deposit and suspension feeding. To deposit feed efficiently on benthic microalgae, Macoma has to live close to the sediment surface, where it can graze an extensive surface area, but is within reach of many predators. Individuals that are more safely buried at a greater depth can only suspension feed, or deposit feed from a small surface area. We expected local differences in burying depth on intertidal mudflats to be caused by differences in immersion time (i.e. time available for feeding, particularly suspension feeding), since immersion time has been shown experimentally to affect body condition positively, and since body condition and burying depth in Macoma are postively related in the field. To test this we experimentally manipulated immersion time, and followed changes in burying depth and body condition. In the experiments, longer immersion time went consistently with greater burying depth of Macoma and higher body condition. On a transect in the western Wadden Sea, the deepest Macoma were indeed found at the intertidal level with the longest immersion time, but these were at that time not the animals with the highest body condition. Within each locality, however, body condition was positively correlated with burying depth. The experimental data and the within-locality data support the hypothesis that longer immersion time may influence burying depth through body condition. However, the fact that between-locality differences in burying depth seemed to be consistently related to immersion time, but not to body condition, indicates that body condition alone does not explain place-to-place variation in burying depth.

The bivalve Macoma balthica is a common species in the Wadden Sea and North Sea. Juveniles temporarily use nurseries in the high intertidal. To explain this nursery use, predation pressure was examined for both juvenile and adult Macoma at low and high tidal flats. The study was carried out in the eastern Dutch Wadden Sea.Shrimps Crangon crangon, adult crabs Carcinus maenas, gobies Pomatoschistus and juvenile flatfish were more abundant and larger on low than on high tidal flats, but 0-group Carcinus was more abundant on the high tidal flats. Crangon and 0-group Carcinus stomachs frequently contained Macoma remains. These predators selectively preyed on small 0-group Macoma, both in the field and in laboratory experiments. The effect of predation by epibenthic animals and birds, on the low and high tidal flats, was examined in exclosure experiments (2 mm mesh). There was no effect of epibenthos exclosure on adult Macoma. For 0-group Macoma, densities were higher in exclosures than in the controls where predators had normal access. The density reduction by epibenthic predators was much larger in the low than in the high intertidal. We found no effect of bird predation on densities of 0- and 1+group Macoma.Thus, 0-group Macoma is under high predation pressure by epibenthos in the low intertidal, especially by shrimps, while they are relatively safe in the high intertidal. However, most of the shellfish outgrow their epibenthic predators during their first summer. Therefore, it becomes safe for the bivalves to redistribute to locations where epibenthic predators are abundant, during their first winter. On the other hand, it did not become clear from this study why many of the larger Macoma leave the high intertidal. Concluding, the nursery use of Macoma-spat in the high intertidal is probably, at least partly, an adaptation to avoid epibenthic predation.

The population development of the 1998 year class of the bivalve Macoma balthicd was studied by repeated sampling of a tidal flat area in the eastern Dutch Wadden Sea from May 1998 to August 2000. The juveniles migrated twice, once in mid-1998 from their primary settlement locations in the low sandy intertidal to the nursery in the high intertidal (spring migration, 25 % of all juvenile Mbalthica relocated from low to high intertidal) and once in late 1998/early 1999 from the nursery to the low intertidal and the subtidal (winter migration, between 8 and 15 % of all 0-group (less than 1 yr old) M. balthica relocated from high to low intertidal). During winter, M. balthica migration was most intensive at the lowest temperatures, Relative to the abundance on the tidal flats, the 1+ group (older than 1 yr) M. balthica (i.e. from the second summer onwards) were rare in the tidal channels of the Wadden Sea and were only slightly more common in the North Sea adjacent to the tidal inlet. During both the spring and winter migration, many bivalves disappeared from the tidal flat population. This could partly be explained by normal mortality and by emigration to the subtidal channels and the North Sea. The remaining mortality was probably due to the risks inherent in migration: predation during pelagic floating or not reaching the right locations, The number of bivalves that disappeared was very high. In spring, slightly more disappeared than relocated. In winter, > 4 times more bivalves disappeared than relocated, Migration is obviously a very dangerous activity, therefore great advantages must be associated with the nursery use that makes such migrations necessary. An analysis of literature data on the density of M. balthica shows that in the eastern Dutch Wadden Sea, 90 % of the population lives in the intertidal, about 10% in the adjacent North Sea, and a negligible fraction in the subtidal channels of the Wadden Sea.

Trace-metal concentrations in sediment and in the clam Macoma petalum (formerly reported as Macoma balthica), clam reproductive activity, and benthic macroinvertebrate community structure were 3 investigated in a mudflat 1 kilometer south of the discharge of the Palo Alto Regional Water Quality Control Plant (PARWQCP) in South San Francisco Bay, Calif. This report includes the data collected by U.S. Geological Survey (USGS) scientists for the period January 2013 to December 2013. These data serve as the basis for the City of Palo Alto’s Near-Field Receiving Water Monitoring Program, initiated in 1994. Following significant reductions in the late 1980s, silver (Ag) and copper (Cu) concentrations in sediment and M. petalum appear to have stabilized. Data for other metals, including chromium (Cr), mercury (Hg), nickel (Ni), selenium (Se), and zinc (Zn), have been collected since 1994. Over this period, concentrations of these elements have remained relatively constant, aside from seasonal variation that is common to all elements. In 2013, concentrations of Ag and Cu in M. petalum varied seasonally in response to a combination of site-specific metal exposures and annual growth and reproduction, as reported previously. Seasonal patterns for other elements, including Cr, Ni, Zn, Hg, and Se, were generally similar in timing and magnitude as those for Ag and Cu. In M. petalum, all observed elements showed annual maxima in January–February and minima in April, except for Zn, which was lowest in December. In sediments, annual maxima also occurred in January–February, and minima were measured in June and September. In 2013, metal concentrations in both sediments and clam tissue were among the lowest concentrations on record. This record suggests that regional-scale factors now largely control sedimentary and bioavailable concentrations of Ag and Cu, as well as other elements of regulatory interest, at the Palo Alto site. Analyses of the benthic community structure of a mudflat in South San Francisco Bay over a 40-year period show that changes in the community have occurred concurrent with reduced concentrations of metals in the sediment and in the tissues of the biosentinel clam, M. petalum, from the same area. Analysis of the M. petalum community shows increases in reproductive activity concurrent with the decline in metal concentrations in the tissues of this organism. Reproductive activity is presently stable (2013), with almost all animals initiating reproduction in the fall and spawning the following spring. The community has shifted from being dominated by several opportunistic species to a community where the species are more similar in abundance, a pattern that indicates a more stable community that is subjected to fewer stressors. In addition, two of the opportunistic species (Ampelisca abdita and Streblospio benedicti) that brood their young and live on the surface of the sediment in tubes have shown a continual decline in dominance coincident with the decline in metals; both species had short-lived rebounds in abundance in 2008, 2009, and 2010. Heteromastus filiformis (a subsurface polychaete worm that lives in the sediment, consumes sediment and organic particles residing in the sediment, and reproduces by laying its eggs on or in the sediment) showed a concurrent increase in dominance and, in the last several years before 2008, showed a stable population. H. filiformis abundance increased slightly in 2011–2012 and returned to pre-2011 numbers in 2013. An unidentified disturbance occurred on the mudflat in early 2008 that resulted in the loss of the benthic animals, except for those deep-dwelling animals like Macoma petalum. Animals immediately returned to the mudflat in 2008, which was the first indication that the disturbance was not due to a persistent toxin or to anoxia. The reproductive mode of most species present in 2013 is reflective of the species that were available either as pelagic larvae or as mobile adults. Although oviparous species were lower in number in this group, the authors hypothesize that these species will return slowly as more species move back into the area. The use of functional ecology was highlighted in the 2013 benthic community data, which show that the animals that have now returned to the mudflat are those that can respond successfully to a physical, nontoxic disturbance. Today, community data show a mix of animals that consume the sediment, filter feed, have pelagic larvae that must survive landing on the sediment, and brood their young. USGS scientists continue to observe the community’s response to the 2008 defaunation event because it allows them to examine the response of the community to a natural disturbance (possible

The persistence of prey encountering intense predation varies by species, prey density, and habitat type; however, the collective impact of these factors has rarely been tested experimentally in natural marine systems. Using the thin-shelled clams Mya arenaria and Macoma balthica as prey, and the main epibenthic predator of whole adult clams, the blue crab Callinectes sapidus, we conducted a series of experiments in Chesapeake Bay tributaries that (1) links field abundance and distribution of bivalve prey species with habitat-specific mortality patterns; (2) represents the first comprehensive field test of species-specific, habitat-specific, and density-dependent mortality for subtidal, soft-bottom, deep-burrowing prey; and (3) thereby enables development of a conceptual model to be used as a heuristic tool linking predator–prey dynamics, habitat type, and evolutionary defense tactics for marine benthos. In 15 years of field monitoring, Mya was more common in sand than mud habitats, and Macoma was widely distributed and at higher densities than Mya in mud and sand. In field experiments, mortality of both Mya and Macoma was density dependent in those habitats where the clams are common. The blue crab population in the field exhibited a type III “guild functional response” on Mya in sand, and on Macoma in both mud and sand. Mortality was lower in sand than mud for Mya, and similar in mud and sand for Macoma, correlating with the high abundances of Mya in sand and Macoma in sand and mud. The persistence of large juvenile and adult bivalves when confronted with intense predation derived substantially from a low-density refuge from predation that varied in a species-specific manner with habitat type, demonstrating the species-specific importance of density and habitat to clam survival. We developed a conceptual model detailing the relative importance of behavior, morphology, habitat features, and the basic components of predator–prey interactions to the survival of bivalve molluscs. At one extreme are bivalve molluscs, such as oysters, that emphasize morphological refuges that increase the predator's handling time. At the other extreme are bivalves, such as Mya and Macoma, that reduce predator encounter rates. The model is intended to be used as a heuristic tool to develop testable hypotheses.

High recruitment of the bivalves Cerastoderma edule, Mytilus edulis, Macoma balthica and Mya arenaria in summer after severe winters is an often reported phenomenon in the Wadden Sea. After the severe winter of 1995/96 however, only Cerastoderma and Mytilus followed this pattern in the Sylt-Romo Bight. Repeated sampling of Cerastoderma, Macoma and Mya following a severe (1995/96), a moderate (1996/97), and a mild winter (1997/98) revealed that early recruitment was highest after the mild winter. In Cerastoderma the eventual high recruitment at the end of summer 1996 was caused by reduced benthic mortality. Low recruitment of Macoma and Mya after the severe winter may have been caused by a higher susceptibility to epibenthic predation and/or a higher susceptibility to passive re-suspension than in Cerastoderma and Mytilus. In all cases, post-settlement processes were decisive for reproductive success.

At large spatial scales (>1 km), the forces structuring marine communities are diverse and include oceanographic, geological, and human processes, as well as availability of regional species pools. Few studies in marine and estuarine systems have examined the joint effects of predation (top-down) and food availability (bottom-up) in controlling populations at these scales. We compared the relative influence of top-down and bottom-up factors to population abundance of the infaunal clam Macoma balthica in two ecosystems differing in spatial extent by an order of magnitude: the York River, 50 km long, and the Rhode River, 5 km long. In both rivers, two habitat types could be differentiated by either high or low density of Macoma. In the York, Macoma abundance was tenfold greater upriver than downriver, predator abundance was greater in the high clam density habitat (i.e. upriver), and predation was only evident where clams were dense (i.e. upriver, where food availability for predatory crabs was elevated). In this large-scale system, predators were apparently unable to travel between upriver and downriver habitats where food availability differed. Moreover, sedimentary carbon (i.e. food for deposit-feeding clams) was significantly greater in the high clam-density habitat; this is consistent with the hypothesis that bottom-up factors principally dictate clam density, and moreover, that clam density drives predator density. In the Rhode River, a smaller-scale system, predators could easily move among habitats differing in clam density. Macoma abundance and predator abundance were both threefold greater in mud than sand. In contrast, predation intensity was higher in sand than mud, consistent with a hypothesis of top-down control. As in the large-scale system, sedimentary carbon was significantly greater in the high clam-density habitat (i.e. mud). In this smaller scale system, both top-down and bottom-up factors contributed to habitat-specific patterns in clam population abundance. Hence, in this marine benthic ecosystem, bottom-up control was important at both large and small spatial scales, whereas top-down control was only important at the smaller spatial scale.

This paper surveys data obtained during 3 decades (1969-1999) of monitoring the macrobenthic fauna of a 50 km 2 tidal-flat area in the Wadden Sea (Balgzand) and compares the annual figures with similar long-term data series from other parts of the Wadden Sea (Groningen, Norderney). Despite enormous year-to-year variability in annual recruitment of particularly the bivalves, total-biomass values were remarkably stable. Detailed data are presented on the annual variability in recruitment success of the 4 most important bivalve species of the Balgzand area (Cerastoderma edule, Macoma balthica, Mya arenaria, and Mytilus edulis). Together these 4 species usually accounted for more than half of the total zoobenthic biomass and largely governed its year-to-year fluctuations. Recruit numbers of the 4 species observed in 27 summers showed similar relationships with the character of the foregoing winter. Such relationships were also observed in other Wadden Sea areas in The Netherlands and Germany. These common relationships resulted in a certain synchrony of recruitment success between the species (within areas) and between areas (within species). Thus, over vast areas (hundreds of km), bivalve recruit densities were generally (though not invariably) high after severe winters and low after mild winters. The resulting strong year-to-year variability in recruit numbers (with standard errors exceeding long-term means) was only just passed on to subsequent total-biomass values for the following 3 reasons: (1) the biomass of any species was generally composed of more than 1 year class, (2) the various species did not reach their maximal biomass at the same age (time elapsed after recruitment), and (3) feedback mechanisms (enhanced reduction of numbers at high abundance) were effective in some species.

Predation by adults of the amphipod Monoporeia affinis on the plantigrade postlarval stage of the bivalve Macoma balthica was studied in the laboratory. We confirmed that M. affinis consumes small M. balthica. Amphipods offered 14C-labelled postlarvae took up the radioactive tracer, while those presented Rhodamine B-stained postlarvae acquired gut contents fluorescing strongly in orange, whereas control amphipods did not. Both labelling methods proved convenient to use in laboratory experiments, and are particularly useful when organisms lack structures that can be easily identified after being ingested, or when cross-over reactions may bias the results of immunoassays. The results reported here support the conclusion from earlier studies that predation by M. affinis on M. balthica can affect population dynamics of M. balthica and is likely to be an important structuring factor in the low-diversity benthic macrofauna community of the Baltic Sea.

Filter-feeding molluscan shellfish can concentrate zoonotic and anthroponotic waterborne pathogens. Cysts of Giardia sp. were detected by immunofluorescent antibodies in tissues of the clams Macoma balthica and M. mitchelli from Rhode River, a Chesapeake Bay (Maryland) subestuary. Molecular tests identified the cysts as Giardia duodenalis Genotype A, the most common genotype recovered from humans. Macoma clams are burrowers in mud or sandy-mud substrata and preferentially feed on the surface sediment layer. Waterborne Giardia cysts settle rapidly to the bottom in slow-moving waters and contaminate the sediment. Macoma clams do not have economic value, but can serve as biologic indicators of sediment contamination with Giardia sp. cysts of public health importance. These clams can be used for sanitary assessment of water quality.

Macrofauna, nutrient fluxes, porewater chemistry and sediment characteristics were measured at six intertidal mudflat sites in the Humber Estuary, U.K., during the different seasons. Nereis diversicolor , Macoma balthica and Corophium volutator were found to be the dominant macrofauna. Salinity was the baseline control on macrofauna distribution but this was overprinted by periodic impoverishment due to sediment mobilization. High resolution gel probe porewater samplers provided direct evidence for the impact of burrows on porewater chemistry. The macrofauna modified nutrient fluxes during periods of mud flat stability. Nereis caused a decrease in silicate and phosphate effluxes but enhanced ammonia release and nitrate uptake. Macoma enhanced ammonia and nitrite release. The impact of Corophium was not possible to discern. The Humber is a large, highly dynamic macrotidal estuary in which sediment resuspension has a large impact on porewater profiles, nutrient fluxes and macrofaunal communities. Simple patterns and inter-relationships which are seen in small sheltered estuaries are not observed in the Humber.

In 1995 the seasonal development of concentrations of both phytoplankton and larvae of the bivalve Macoma balthica was studied in the coastal zone behind the back-barrier island of Spiekeroog (German Wadden Sea). In July/August larvae reached maximum concentrations of about 1000 to 4200 ind. m −3 (depending on the sampling site and tidal period), probably in relation to a phytoplankton bloom in July. This observation of an unusually late maximum of Macoma larvae is discussed in detail in connection with the recent literature available about spawning of M. balthica in the Wadden Sea.

Predation on bivalve spat (Macoma balthica, Cerastoderma edule and Mya arenaria) by crustaceans was studied in an intertidal area in the western Dutch Wadden Sea in 1993. In all species settlement started at the end of April. Peak numbers were reached in the beginning of June of about 4300 ind. m−2 in Macoma, 1300 in Cerastoderma and 500 in Mya. During June and July numbers dropped sharply to low levels at a mean size of 1.0 to 1.5 mm. Instantaneous mortality rates over this period varied from 0.045 d−1 in Macoma to 0.056 d−1 in both Cerastoderma and Mya. Immunoassays of gut contents of brown shrimps Crangon crangon and shore crabs Carcinus maenas positively identified both species as predators on bivalve spat. The high shrimp densities observed (100 ind. m−2) in combination with their simultaneous presence with the post-larval bivalves indicate that juvenile shrimps are likely the most important predator. The estimated predation pressure by crustaceans, and especially the brown shrimp, is sufficient to account for the observed mortality rates among bivalves. Bivalve recruitment, however, did not appear to be regulated by crustacean predation: during the period of predation, bivalve mortality was not density-dependent. Information on bivalve predation in Swedish bays support this view.

On intertidal flats in north-west Europe, the bivalve Macoma balthica buries deep in the sediment in early winter, but ascends to the surface in late winter. Close to surface Macoma runs the risk of being eaten by epibenthic predators. We hypothesise that living shallow leads to more rapid growth in spring by allowing for higher food-intake rates. In three experiments, of which two took place in the field, we placed Macoma at fixed burying depths. We measured body mass and survival after 10–16 weeks. At the end of all three experiments, body mass of shallow-buried animals was significantly higher than that of the surviving deep-buried animals. Survival was lowest in the animals buried deepest; deceased animals may have died of starvation and/or perhaps suffocation. In the mesocosm experiment there was a negative relationship between burying depth and feeding (grazing) radius. Our experimental results are consistent with the idea that Macoma comes to the surface to feed efficiently in order to grow fast.

A model was developed to describe the erosion of a cohesive sediment within an annular flume. The model relates the rate of resuspension of sediment per unit area to the difference between the amount of sediment available for resuspension from the bed and the amount already resuspended into the water column. The rate of erosion also depends on the excess free-stream near-bed current velocity above a critical threshold velocity. The basic five parameter model describes 96% of the variation in suspended sediment concentration within the flume, where natural sediment is exposed to increments in current velocity (up to 43 cm s−1, equivalent to a shear stress of 1.5 Pa) in the absence of macrofauna. The addition of a small clam, Macoma balthica, to the experimental system led to increased levels of resuspension at all velocities. This effect increased asymptotically with Macoma population density and could be modeled using two additional parameters. Complete analysis of the resulting seven-parameter model showed that the effect of the fauna was confined solely to the amount of sediment available for resuspension. Field data supported the laboratory-determined functional relationship between Macoma density and the quantity of sediment resuspended at environmentally realistic maximum current velocities and provided field-based parameter estimates for modeling the erosion of in situ sediment. Using predicted flood and ebb tidal current velocities along a 3.5-km transect normal to the shore, we determined the potential impact of Macoma on the amount of sediment resuspended over a single tidal inundation. We estimate that natural densities of Macoma increase the amount of sediment resuspended, at our sites above midtidal shore level, by 0.42 kg m−2 per tide. We suggest that experimental flume studies, which can include field deployments, combined with this parametersparse model of fauna1 impact on sediment resuspension provide a straightforward means of quantifying the complex effects of biotic components on rates of sediment erosion.

Predation by juvenile 1+flounders, Platichthys flesus , (mean total length 8.0 cm±0.6 cm SD) on juvenile Macoma balthica (mean length 1.94 mm±0.40 mm SD) and Bathyporeia pilosa (mean length 4.11 mm±0.47 mm SD) was studied in a series of aquarium experiments. Prey vulnerability and consumption, as well as possible switching behaviour by the predator, were studied with varying total and relative prey densities. The functional response of the predator was also determined from the experimental results. The consumption and vulnerability of both prey species were equal when the prey species were presented separately to the predators (50 ind/aq). In the comparable two-prey-species experiment, where equal proportions of the prey species were presented to the predators, total prey consumption was about the same as in the single-prey-species experiment. Prey consumption during the night was clearly lower than prey consumption during the day with the same prey density. In all experiments, juvenile flounder showed a slight preference for Macoma before Bathyporeia independently of the relative or absolute prey density. No switching behaviour was observed. The consumption of both Macoma and Bathyporeia increased significantly with increasing total prey density. The functional response of flounder was in both cases of the type III. The best fit of the data was achieved with a continuous model of the type-III response.

Results of experiments are reported on the effects of water temperature and immersion time in winter on egg size and egg numbers in three intertidally living bivalves in the Dutch Wadden Sea, the Baltic tellin Macoma balthica , the common cockle Cerastoderma edule and the common mussel Mytilus edulis . Macoma (14–17 mm shell length) produced large eggs (diameter of 107 μm) in relatively small numbers (20 000–70 000) in early spring. Later in spring, Cerastoderma (28–33 mm shell length) produced smaller eggs (77 μm, excluding the surrounding jelly layer) in tenfold larger numbers (200 000–700 000). Mytilus (45–55 mm shell length) spawned even smaller eggs (72 μm) in high (but not easily assessed) numbers over a more extended period. In Macoma egg size was not affected by winter temperatures or immersion time. Effects of winter–spring temperatures and immersion time on egg size could be demonstrated in Cerastoderma . Smaller eggs were produced at the higher temperatures. Effects of immersion time were non-consistent: at lower water temperatures larger, but at higher temperatures smaller eggs were produced by animals kept at longer immersion times. In Mytilus , no temperature effects were observed. However, a longer immersion time resulted in larger eggs. In Macoma as well as in Cerastoderma significantly more eggs were produced at the lower temperature. Immersion time effects were most pronounced at the lower temperature, where more eggs were produced at the subtidal level than at the tidal level. At the higher water temperature differences between egg numbers produced at the two tidal levels were small. Just prior to spawning, egg numbers were strongly positively related to body mass at a certain shell length.

In a set of field and laboratory experiments, the relative importance of (1) direct predation (measured as mortality in the prey populations), (2) physical disturbance of the sediment (sand and mud), and the combined effects of disturbance and predation, and (3) sublethal siphon cropping, were tested on an infaunal food web in the low-saline northern Baltic Sea. The predators used (Saduria entomon and Crungon crangon) are the major epibenthic crustacean predators of the northern Baltic coastal waters, and the prey organism in the experiments (the bivalve Macoma balthica) is, by frequency of occurrence and by biomass, the dominant infaunal organism among the zoobenthos. In the field the predatory effect of Saduria was tested on the entire infaunal community. The field experiment on direct predation by Saduria on the entire infaunal assemblage significantly reduced the density of the polychaete Manayunkia aestuarina. Aquarium experiments show that although direct predation by Saduriu or physical sediment disturbance alone had little effects on juvenile ( < 3 mm) Macoma, the combined effects of these factors were significant, and more important than the sum of the two single factors, demonstrating synergistic negative effects. Experiments with Saduria and Crungon in relation to adult (7-17 mm) Mucoma showed sublethal effects on length-weight relationships and on a general index of condition in the mussels. The experiments illustrate that intricate combinations of biotic and physical (environmental) mechanisms may play important roles in the organization of zoobenthic communities.

1. Knots Calidris canutus are high-arctic breeding shorebirds which spend the nonbreeding season in intertidal areas where they feed on small buried molluscs which are swallowed whole. We tested whether their intake rate can be adequately described by a functional response model (the disc equation of Holling) assuming prey detection by direct touch. 2. Knots were fed two bivalve species (Macoma balthica and Cerastoderma edule) of different size and at different density and in Macoma at variable depth on small areas of soft Sediment. Five different individuals were used in feeding trials during which six prey were allowed detection and ingestion. 3. Knots perfectly obeyed the two basic assumptions of Holling's disc equation: neither the instantaneous area of discovery nor the handling time changed with variation in prey density. 4. However, two predictions for prey perception by direct touch (that the instantaneous area of discovery is a positive function of shell size and a negative one of prey depth) were rejected. The instantaneous area of discovery was usually also higher than predicted from the area touched by probing knots. 5. Knots may, therefore, use a 'remote sense' to locate buried hard-shelled prey. Gerritsen, van Heezik & Swennen (1983) showed that knots do not use taste to discover bivalves at a distance. We argue that the detection involves a self-induced pressure mechanism rather than a passive sense for vibrations, since it is unlikely that static bivalve prey emit such signals just after experimental handling. 6. Whatever the exact prey detection mechanism, the recorded (high) value for the instantaneous area of discovery of deep-living bivalve prey is in accord with the observation that knots use large areas of intertidal flat in the western Dutch Wadden Sea where bivalve stocks are too low to support knots according to a previous functional response model invoking direct touch.

We conducted a laboratory experiment to investigate the effects of drifting algal conglomerates on meiofauna and how its response to the presence of various macrobenthic species was modified by them. We mimicked a situation which is common in the archipelago area of the Baltic Sea, where algal mats become stagnant in shallow embayments, covering wide areas in whose centre hypoxic and even anoxic conditions develop rapidly. We used three macrobenthic species: Macoma balthica, Hediste diversicolor and Marenzelleria spp., which have shown different tolerance degrees to the drifting algae. In our experiment, drifting algae caused a major decline in sediment meiofaunal abundance and changes in the community structure, both with and without the three macrobenthic species under analysis. Of the three macrobenthic species, Marenzelleria spp. seemed to have a higher tolerance to low oxygen levels induced by the algal mats, while M. balthica and H. diversicolor mortality increased after 6. days under the algae. Both Hediste and Macoma seemed to exert a double facilitating effect: into the sediment, probably by increasing oxygen levels in deeper layers and through sediment reworking; and into the algae, via disturbance of surface layers, enhancing meiofaunal escape to the algal mass and probably their survival from the hypoxia induced below. Hediste also caused a decrease in harpacticoid copepod abundance, presumably through predation, and this was also the case for Marenzelleria in whose presence the abundance of copepods, but also turbellarians, was drastically reduced. The so far undocumented dramatic effect caused by drifting algae on meiofauna populations in our experiment shows how the negative impact of hypoxia induced by drifting algal mats (eutrophication) is propagated to almost all levels of the trophic and functional chain, influencing species interactions even at the lowest levels. This might be especially important in low diversity systems such as the Baltic Sea, were species and functional diversity are already depauperated. © 2012 Elsevier B.V., This study was supported through a MARS travel award, a CIMO grant from the government of Finland and a European Community Mari Curie fellowship (EVK-CT-2002-50019) to the first author, and by the Foundation for Åbo Akademi University for support to KA and EB. E. Ólafsson is acknowledged for comments on an earlier draft of this paper.

In the course of 1990, stocks of mussels ( Mytilus edulis ) declined to unprecedentedly low levels in the Dutch Wadden Sea. Hardly a wild mussel bed was left on the tidal flats as a consequence of three years (1988, 1989, and 1990) with failing recruitment and intensive fishing for seed mussels. During these three years, recruitment of cockles ( Cerastoderma edule ) also failed, whereas fishing was continued. Bird species taking these bivalves as staple food, the oystercatcher ( Haematopus ostralegus ) and the eider ( Somateria mollissima ), experienced food shortage. Significant numbers of eiders left the Dutch Wadden Sea area or died, whereas oystercatchers remained abundant trhoughout the winter in most of the Dutch Wadden Sea. Alternative prey species of oystercatchers experienced unsually high mortality rates in the appropriate size classes. This was so in all other common species of bivalves, viz. first-year and older cockles, adult Macoma balthica , and juvenile Mya arenaria . This led to minimal stocks of food for oystercatchers in the late winter of 1991. In March 1991, cockles were depleted and the combined stocks Mya and Macoma would soon have run out of food supply to the overwintering oystercatcher population. Apparently, oystercatchers are able to reduce the stocks of their various bivalve prey species to very low levels.

The effect of surface deposit-feeder ( Macoma balthica L.) density on chlorophyll a concentrations in shallow (2.5–3.5 cm deep) sediment microcosms was examined. The experimental design simulated subtidal, unilluminated sediments without benthic algal primary production, where sedimentary chlorophyll a is not necessarily within viable algal cells. Changes in depth of the visual Redox Potential Discontinuity (RPD), fluorometrically-determined levels of chlorophyll a and phaeopigments and bivalve condition were monitored at weekly intervals for 42 days. Sampling was conducted by multiple coring in replicate containers at 4 Macoma densities (0, 370, 741 and 1111 individuals · m −2 ). Cores were sectioned vertically before analysis. Bivalve density had no effect on the depth of the visual RPD. M. balthica had no persistent effect on sedimentary chlorophyll a levels at natural bivalve field densities. Evidence that bivalves were either not using chlorophyll a -containing particles as a primary food source, or the absorption efficiency of chlorophyll a by the bivalves was low includes: (1) chlorophyll a concentrations did not decline specifically within the surface feeding area, (2) phaeopigment concentrations were not elevated, and (3) bivalve condition was affected negatively in some treatments without a corresponding change in chlorophyll a concentrations. In benthic habitats lacking primary production, where chlorophyll a input depends upon sedimentation, abundant, surface deposit-feeding bivalves, such as M. balthica , may have little influence on sedimentary chlorophyll a concentrations.

In August–October 1988–1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10 000 to 25 000 birds. Over 100 000 knots were recorded on three occassions. Knots feed in large flocks, individual birds usually experiencing 4 000 to 15 000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964–1992 there were no clear trends in the number of knots, but canutus -knots were particularly abundant in July–August 1991, whereas in 1992 both subspecies were absent. Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distributon of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m 2 ) and Cerastoderma , and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the Western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km 2 , much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10–15 km 2 ), a difference that is correlated with prey spectrum, prey availability and predictability.

Representatives of the family Tellinidae stand out among Bivalvia because of the brightness and variety of their shell color. M. balthica , a common representative of the shallow-water infauna of boreal and subarctic seas exhibits intraspecific variation of shell color. This variation was formally described and interpreted as genetic polymorphism by Cain [6]. Shell color was used as a genetic character in some population studies of macoma [3, 5, 10]. Until now, no hypotheses on the mechanisms of shell color inheritance have been advanced. In the present work, a hypothetical scheme of the shell color inheritance is suggested and the spatial pattern of the color morph frequencies in populations of the mollusks from the White and Barents seas is analyzed. We analyzed 12 quantitative samples of M. balthica from different parts of the White and Barents seas (Fig. 1). The sample size varied from 58 to 275 specimens, all of them older than three years. The color of the inner side of the shell was determined. Four qualitative variants of the shell color were found in macomas from the White and Barents seas: the white, red, orange and yellow morphs. We consider this variation to be combinatorial, regarding the presence or absence of a pigment in the shell (white or not white) and the color of the pigmented shells as two independent characters: “presence of a pigment” and “shell color,” respectively. It seems unnecessary to introduce additional characters to this scheme, such as the “dichromancy of the shell” (when the top of the shell is pigmented brighter) and the intensity of pigmentation. These characters varied only in some of the samples, and this variation was not qualitative. The following genetic interpretation of the polymorphism is suggested. The color of pigmented shells is determined by two pigment forms: yellow and red. Synthesis of the pigments and their deposition in the shells are determined by a unique diallelic “shell color” locus. Homozygotes for one allele have red shells, homozygotes for the other allele have yellow shells. Heterozygotes deposit both pigments in their shells, and their color is orange. The possibility of expression of the “shell color” locus is determined independently by one or several loci. Nonpigmented (i.e., white) specimens could not be genotyped with respect to the “shell color” locus.

Spatfall of the tellinid bivalve Macoma balthica may occur in fine-grained sediments at different tidal elevations in the Wadden Sea. but it is not clear which mechanism (active habitat selection or passive sinking of larvae, or both) can explain the observed distribution pattern. Spatfall and the subsequent development of juvenile abundances and size distribution were studied along a transect in the northern Wadden Sea near the Island of Sylt. Initial spatfall was highest in the lower intertidal and correlated significantly with hydrographic parameters. The enhanced larval settlement observed in dense aggregates of the tube-building polychaete Lanice conchilega confirmed the prominent role of hydrographic factors in initial spatfall. Subsequently, abundance strongly decreased in the lower intertidal but increased in the upper intertidal due to immigration of newly settled spat from lower sites. By the end of October, abundance was higher in the upper intertidal. Growth of the juveniles was higher in the upper intertidal. It is suggested that (1) initial spatfall is mainly ruled by hydrographic factors without active sediment selection; (2) young Macoma remain highly mobile during the first weeks of their benthic life and by byssus drift may achieve a net transport into areas with weak initial spatfall; (3) at the end of their first winter a second period of high floating activity occurs, bringing them back towards the lower intertidal and shallow subtidal. Thus, by successive postlarval migrations Macoma may several times change the intertidal site occupied during their first year of life. The comparatively low interannual variability of recruitment success noted in this species in the Wadden Sea may be a result of these migrations.

Halifax Harbour sediments contain heavy metals and organic contaminants. To assess the biological effects of these compounds in the sediment, seven sites spanning a range of known sediment types, water depths, metal levels, and organic contaminant levels were chosen for assessment by a series of tests. Sediment toxicity was measured by the reduction of microbial luminescence (Photobacterium phosphoreum) in three Microtoxr tests (pore water, solvent extract, and solid phase), by the percentages of survival and reburial in two amphipod species (Rhepoxynius abronius and Corophium volutator), and by the survival and change in biomass of juvenile polychaete (Neanthes sp.). Uptake of contaminants from sediment was assessed by a bioaccumulation test, using a bivalve mollusc (Macoma balthica). The chronic effects of the sediment on bottom-dwelling fish were assessed by histopathological studies on winter flounder (Pseudopleuronectes americanus) collected from the harbor. The results of this study showed detectable biological effects of the Halifax sediments on two (Photobacterium phosphoreum and Rhepoxynius abronius) of the four species of tested organisms. These effects were associated with high concentrations of polynuclear aromatic hydrocarbons (PAHs) in the harbor sediments. The order of sensitivity for the various sediment toxicity tests was Microtox solvent extract = Microtox solid phase > Rhepoxynius abronius > Microtox pore water > Corophium volutator = Neanthes sp. Mortality in Macoma was increased, although no significant uptake of contaminants was detected in the bioaccumulation test. Hepatic lesions were observed in winter flounder collected from the harbor, suggesting a chronic effect of the contaminated harbor sediment.