Bivalve Arctica Islandica Research Articles

Sclerochronological records of Arctica islandica from the inner German Bight

Sclerochronological records of interannual shell growth variability were established for eight modern shells (26 to 163 years of age) of the bivalve Arctica islandica, which were sampled at one site in the inner German Bight. The records indicate generally low synchrony between individuals. Spectral analysis of the whole 163-yr masterchronology indicated a cyclic pattern with a period of 5 and 7 years. The masterchronology correlated poorly to time series of environmental parameters over the last 90 years. High environmental variability in time and space of the dynamic and complex German Bight hydrographic system results in an extraordinarily high ‘noise’ level in the shell growth pattern of Arctica islandica.

Copepods link quahog growth to climate

From samples collected in 1983, 1991 and 2000, a long-term growth record for the bivalve Arctica islandica from the northern North Sea was constructed with methods derived from dendrochronology. Subsequent response-function analyses demonstrated that shell growth was mainly influenced by the abundance of copepods as recorded by the CPR survey. In years with dense copepod populations a major part of the downward flux of food particles is intercepted by the copepods before it reaches the seafloor. This may lead to a shortage of food for A. islandica resulting in a depression of shell growth. Although the abundance of copepods in the northern North Sea is linked to climate there is only a weak statistical relation between shell growth and climate.

The distribution and population structure of the bivalve Arctica islandica L. in the North Sea: what possible factors are involved?

The present paper summarises observations on the distribution, abundance and population structure of the bivalve Arctica islandica in the North Sea between 1970 and 2000, and demonstrates that Arctica has a widespread distribution in the North Sea north of 53°30′N. Along its southern and eastern borders the distribution seems to be limited to depths beyond 30 m. A comparison between distribution patterns of Arctica in 1972–1994 and in 1996–2000 suggests slight changes along its southernmost border in the Oyster Ground. In the south-eastern North Sea, the average density of Arctica (>10 mm) was 7 individuals per 100 m 2 and the population was dominated by full-grown specimens exceeding 50 mm shell height. The highest abundance of spat, juveniles and adults was found in the deeper central section of the Oyster Ground that is stratified during summer. There, the mean density was 21 individuals (>10 mm) per 100 m 2. These densities were much lower than in the northern North Sea (Fladen Ground), where abundance was one to two orders of magnitude higher and peaked at 28 600 individuals per 100 m 2. In the Fladen Ground, the population structure was bimodally shaped and dominated by juveniles. In the Oyster Ground, the skewed size class distribution suggests that the recruitment to larger size classes is hampered. An insufficiently dense stock of reproducing adults generating less dense spatfalls, possibly in combination with limited survival of spat and juveniles, prevents successful recruitment. Although natural processes may contribute to the skewed population structure, intensive bottom trawling is thought to have a major effect as well. It is therefore questionable whether under present-day conditions the population of Arctica in the SE North Sea can be considered sustainable in the long term.

Post-glacial depositional environments in a mid-high latitude glacially-overdeepened sea loch, inner Loch Etive, western Scotland

A high-resolution seismic and gravity coring survey has been conducted on inner, and part of outer Loch Etive, a 30 km long, 150 m deep sea loch on the west coast of Scotland. The seismic reflection profiles reveal a 30–60 m thick sediment pile that has accumulated on the floor of the loch since the last (Younger Dryas stadial) glacial re-advance 11–10 ka BP. Four seismic facies have been identified grouped into two seismic sequences, A and B, which are separated by a distinct reflector termed ‘E1’. A highly reflective facies is interpreted as direct river input, an acoustically well-laminated, draped facies interpreted as fine-grained river sediments and a well-laminated to transparent facies interpreted as glaciomarine and glaciolacustrine. Throughout the loch, methane gas-rich sediments occur producing a chaotic seismic facies. The transition from glacially-influenced to river-dominated deposition is displayed by the seismic reflector E1. Core analysis identified eight lithofacies. The oldest sediments are grey muddy sands and olive sandy silts, overlain by younger laminated greeny-grey muddy sand and greeny-grey and greeny-black homogeneous watery sandy mud. Abundant shell material is present throughout, notably the bivalve Arctica islandica, from which a 14C age of 9490±90 yr BP was obtained from the laminated greeny-grey muddy sands. The sediments are interpreted as being of glaciomarine and glaciolacustrine (Younger Dryas to early-mid Holocene) and more modern riverine-derived origin (mid-latest Holocene).

Ontogenetic trends in aspartic acid racemization and amino acid composition within modern and fossil shells of the bivalve Arctica

Ontogenetic trends (umbo to growth edge of shell) in aspartic acid (Asp) racemization and amino acid composition and their evolution over time are examined in serial samples of annual growth bands from a time-series of three live-collected and two fossil (ca. 500 and 1000 y BP) shells of the long-lived bivalve Arctica islandica. The rate of Asp racemization is shown to be higher in the umbonal portion of the shells (laid down when the clams are young) but constant from a biological age of 10 to 20 y to more than 100 y. Corresponding changes are also seen in amino acid composition and concentration: with increasing biological age of the clam: total amino acid concentration increases substantially, the acidic amino acids Asp, glutamic acid, and alanine decrease in relative concentration (mole-percent) and more basic amino acids including tyrosine, phenylalanine, and lysine increase in relative concentration. These ontogenetic trends are generally retained in the fossil shells. These trends may reflect changing protein composition related to changes in growth rate. Clams grow considerably faster in their youth than when they are older, as indicated by changes in the annual growth increments. Production of more acidic proteins, which play a role in crystal growth, may be favored during the phase of faster growth, whereas more structural proteins, perhaps enhancing structural strength of the shell, may be favored during later growth. These ontogenetic differences in protein composition affect the observed rates of racemization of the protein pool. Some weak diagenetic trends in amino acid composition and abundance may be represented in the time series of shells. These results emphasize the importance of standardization of the location from which samples are taken from shells for dating by amino acid racemization analysis.

Geographical differences in growth rates of Arctica islandica (Mollusca: Bivalvia) from the North Sea and adjacent waters

Geographical differences in the shell growth rate of several populations of the bivalve Arctica islandica (Mollusca: Bivalvia) were estimated by using the growth lines laid down during their first ten years of life. Attention was focused on populations from the North Sea, but for comparison small samples from adjacent waters were also analysed. A four-fold difference in the average growth rate was found between the slowest and fastest growing shells.Principal component analysis was used to summarize the inter-relationships between environmental variables and growth rates. Shell growth correlated positively with primary production and temperature and inversely with depth and the silt content of the sediment. The North Sea specimens were found to have a strong positive correlation with grain size. Since sediment characteristics also depend on bottom currents, it is suggested that these increased rates reflect lateral seston flux as additional food supply.In a multiple regression model, applied to all available data, average annual temperature, primary production and the interaction between production and water depth explained 50% of the variance. The derived standard coefficients for temperature, primary production and the interaction between depth and primary production were 0.90, 0.47 and −0.92 respectively. The results of this study suggest that the temperature effects on in situ shell growth are easily overruled by other environmental factors.If a similar model was calculated with North Sea data only, 75% of the variance was explained by temperature, primary production and depth×primary production. The standard coefficient for primary production was 1.26. The role of temperature in explaining the observed growth differences is negligible since the standard coefficient is −0.098. The interaction term, depth×primary production had a standard coefficient of −0.95.

Growth parameters of a benthic suspension feeder along a depth gradient across the pycnocline in the southern Kattegat, Denmark

Recent findings that a significant part of the pelagic primary production in the Kattegat may occur in the pycnocline raised the question of whether or not this causes increased input of energy to the benthos in the area where the pycnocline comes into contact with the bottom. With this question in mind, comparative studies were made of somatic growth, condition and gut content of the filter feeding bivalve Arctica islandica and of gross community vanables of total fauna at stations along a transect across the area where the pycnocline usually has contact with the bottom. Gut content and condition were measured in March/April, May and September 1992, concomitantly with studies of hydrography and pelagic biology. Growth was estimated by measuring internal growth rings in the shells on individuals of different sizes, yielding average estimates from several years. Temporal variahon of chlorophyll a in the bottom water and chlorophyll gut content in A, islandica showed a similar pattern with the highest values in March/April and the lowest In September. Growth rates in terms of shell size of premature individuals ( 100%. The data does not support the expectation of a direct simple relation between pycnocline production and A. islandica growth, and different reasons for this are discussed.

The long‐lived mollusc Arctica islandica: A new paleoceanographic tool for the reconstruction of bottom temperatures for the continental shelves of the northern North Atlantic Ocean

The carbonate shell of the bivalve Arctica islandica has been recognized, for more than a decade, as a potentially important marine geochemical biorecorder owing to this species' great longevity (200+ years) and wide geographic distribution throughout the northern North Atlantic Ocean, a region vital to global climate and ocean circulation. However, until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species. Using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry, a stable oxygen isotope record (1956–1957 and 1961–1970) has been obtained from a live‐captured, 38‐year‐old A. islandica specimen collected near the former position of the Nantucket Shoals Lightship (41°N. 69°W). The shell's δ18O signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period. The results show that A islandica's δ18O record (1) is in phase with its growth banding, confirming the annual periodicity of this species' growth bands, (2) is in oxygen isotopic equilibrium with the ambient seawater, (3) shows a consistent shell growth shutdown temperature of ∼6°C. which translates into an ∼8‐month (May–December) shell growth period at this location, and (4) records the ambient bottom temperature with a precision of ∼±1.2°C. These results add important information on the life history of this commercially important shellfish species and demonstrate that A. islandica shells can be used to reconstruct inter‐ and intra‐annual records of the continental shelf bottom temperature.

Biomass and activity of benthic fauna on the fladen ground (northern North Sea)

During May 1983 the abundance and biomass of macrobenthos and meiobenthos populations, as well as the metabolic activity (shipboard incubated and in situ measured respiration, and potential respiration activity by ETS) were studied in the Fladen Ground area. Macrofauna showed an abundance of 4500 specimens per m 2; the corresponding biomass was 10.7 g ash-free dry weight per m 2. The bivalve Arctica islandica, with 12 specimens per m 2 contributed 7.2 g to this biomass. Average meiofauna numbers, 0.9·10 6 per m 2 were low; a meiofaunal biomass of only 0.3 g was estimated. Depending on the method applied, large variations in metabolic activity were found. Results from shipboard incubation experiments probably present a large underestimate. The in situ bell-jar experiments showed an average oxygen uptake of 1010 μmol O 2·m −2·h −1, equalling a carbon demand of 7.3 gC·m −2·month −1 in May. ETS measurements gave a 3 times higher estimate. Taking into account that macrofaunal and meiofaunal abundance and biomass, as well as bottom temperatures, show minimum values in spring, an annual carbon mineralization by the benthic system of 50 to 70 gC·m −2 is suggested. This would mean that about one third of the total primary produced organic matter is channelled into the benthic system.

A note on the growth of Arctica islandica

In conjunction with a tagging experiment on Callista chione (L.) in 1976, a small number of the large bivalve Arctica islandica (L.) (Family Arcticidae) were also tagged in a similar manner with plastic discs cemented on to the shell with fast-setting cyanoacrylate adhesive. Arctica is less common in Whitsand Bay than Callista but extends into deeper water, 50–60m. Holme (1953) suggested that the species is long-lived and produced spat infrequently. A few young Arctica have been taken in Whitsand Bay (length 29–37 mm) and also, more commonly, specimens of 80–100 mm. In 1976 five Arctica were tagged and relaid, three of these were recovered in 1977 and one in 1978. Three more were tagged in 1978 and searched for without success in 1979. The recovered specimens did not appear to have moved at all. The results of shell length measurements, though meagre, indicated that growth was very slow. For a shell of 82 mm length the increase was 1–5 mm in a year. For a shell of 101 mm there was no increment after two years. For a shell of 102 mm the annual increment was probably 0-1 mm. In this instance it seems likely that the original length should have been 102–3 mm instead of 103–2 which was recorded. For a shell of 108 mm an increment of 0–3 mm was found after 12 months. From these results the average increment of shells over 100 mm length is likely to be of the order of 0-1 mm per year.

Effects of hypoxia and body size on the oxygen consumption of the bivalve Arctica islandica (L.)

The relationship between oxygen consumption and body weight has been examined in Arctica islandica (L.). Large Arctica exhibit a high degree of respiratory independence under hypoxic conditions; like other species studied, respiratory independence increases markedly with increasing body size. Respiratory independence can also be modified by temperature and physiological condition and it is concluded that the division of species per se into oxygen regulators and oxygen conformers is not merited. These terms describe only the extremes of what is a variable capacity to maintain respiratory independence during hypoxia.

A Statistical Model Relating the Oxygen Consumption of a Mollusk (Littorina littorea) to Activity, Body Size, and Environmental Conditions

A Statistical Model Relating the Oxygen Consumption of a Mollusk (Littorina littorea) to Activity, Body Size, and Environmental Conditions