Age determination of the soft-shell clam Mya arenaria using shell internal growth lines

Shells of known-age Mya arenaria have revealed an internal annual growth pattern in this bivalve. The number of external growth rings on the shell exterior does not correspond to the age of the clams. This study provides an alternative method to using external annual rings for age determination. The internal growth lines are visible in thin sections when the shells are cut from the umbo to the ventral margin. The lines are formed by late spring of each year prior to spawning and are probably in response to decreased winter growth. When the 7 year olds were examined it was difficult to distinguish the most recent growth line and the inner shell layer. This could result in ages being underestimated. This annual pattern of internal growth lines could be useful to biologists and paleoecologists engaged in population studies.     

Population dynamics of the soft-shell clam Mya arenaria

A life table was constructed for Mya arenaria from Gloucester, Massachusetts, USA, based on schedules of age-specific fecundity and mortality determined under natural conditions. Mortality rates decrease with size and age in this species, with the period of maximum mortality occurring during the summer months. Mortality rates during the fall and winter were considerably lower, perhaps due to the inactivity of natural predators. The survivorship curve for M. arenaria approximates the Type 3 curve of Deevey (1947). Mean life expectancy is low in recently-settled clams, peaks when the individual reaches 30.0 to 34.9 mm (1 year of age) and remains fairly high for most of the remainder of life. The intrinsic rate of natural increase (r _max) is very high: 4.74. This enormous rate of potential increase is offset by high rates of larval mortality in the plankton. Unlike the reproductive values of most animals studied, those in M. arenaria peak late in life, well after the know age of first reproduction. This is probably the result of increased fecundity with age. The implications of this work in the area of resource management are discussed.     

Induced triploidy in the soft-shelled clam Mya arenaria: energetic implications

Given that triploid adult bivalves reportedly grow larger and faster than their diploid siblings, such differences should be traceable to variation in energy allocation. In one proposed mechanism, retarded gametogenesis found in triploid adults may allow them more energy for somatic growth. Another hypothesis states that triploids are more heterozygous; increased heterozygosity has been positively correlated with enhanced growth. Juvenile soft-shelled clams, Mya arenaria, were treated with cytochalasin B to induce triploidy and examined with respect to components of a balanced energy equation (C=P+R+E). The variables measured were oxygen uptake (V _{o 2}), filtration rate (FR), dry tissue weight, shell length, shell height and shell inflation. Energy budgets were constructed and diploid and triploid groups compared. Few significant differences were found between diploid and triploid juvenile clams with respect to energy budget components. However, at seven loci assayed electrophoretically the triploid individuals were nearly twice as heterozygous as their diploid siblings. Moreover, tripoloid variances were less than diploid variances for every variable measured. Increased heterozygosity has been correlated with the decreased variance of morphological parameters. This study is believed to be the first to show decreased variance of physiological properties as well as morphological characters. Overall the data clearly indicate that energy allocation in juvenile M. arenaria is not related to ploidy.     

Toxicity evaluation of a complex metal mixture to the softshell clam Mya arenaria

Adults of the softshell clam Mya arenaria were continuously subjected to a flowing raw seawater solution containing a mixture of salts of manganese, zinc, lead, nickel, copper, and cadmium. Final calculated concentrations, in g l^-1, of the toxicant solution were 7200 Mn, 2500 Zn, 70 Pb, 50 Ni, 50 Cu and 1 Cd; these concentrations approximated highest measured levels within surficial interstitial sediment waters from mid-Narragansett Bay, Rhode Island. M. arenaria were also subjected to a 20% solution, i.e., 1440 Mn, 500 Zn, 14 Pb, 10 Ni, 10 Cu, and 0.2 g l^-1 Cd. One study was conducted for 112 days in winter at 0° to 10°C and another for 16 days in summer at 16° to 22°C. In the winter study, all clams exposed to a 100% solution died between the 4th and 10th week; soft parts of survivors at 6 weeks contained about 19 times more Pb, 15 x more Zn, 12 x more Cu, 10 x more Mn, 3 x more Ni and 0.1 x more Cd than controls; relatively minor changes in whole body elemental content of Ca, Cr, Fe, K, Mg, Na, Sr, and V were observed. Clams exposed to a 20% solution during winter survived the 112 day study; at that time these contained about 5 x more Cu, 4 x more Mn, 3 x more Zn and about 2 x more Pb than controls; comparatively minor changes were observed in other elements examined. In the summer study, all M. arenaria subjected to the 100% solution died between 6 and 14 days; survivors from this group at 7 days contained about 25 x more Pb, 13 x more Cu, 11 x more Zn, 7 x more Mn, and 3 x more Ni than controls; other changes in elemental content were not as pronounced. Mortality in the 20% group during summer was slightly higher than controls during the 16 day study; at 14 days survivors from this group contained about 12 x more Mn, 7 x more Pb, 7 x more Zn, 4 x more Cu, and 3 x more Ni than controls. Survival and bioaccumulation patterns were not altered through feeding a supplemental diet of algae. The significance of these findings are discussed in terms of potential environmental perturbations, especially local dredging practices.     

The capacity of the filter-feeding bivalve Mya arenaria L. to affect water transport in sandy beds

Benthic filter feeding macrofauna organisms may be an important factor linking sediment and water column. Transport of water and concomitantly of suspended matter is directly related to the size of the benthic filter feeding population. This paper aims to determine the potential for water transport by the bivalve Mya arenaria along a coastal stretch of roughly 100 km length in the southern Baltic Sea. Quantification of population filtration rates specific to the area is based on distribution, abundance and biomass of M. arenaria and calculated according to previously published filtration rate–biomass relations. Calculated rates range up to >8 m³ m^–2 day^–1 (at 5–20 m water depth in sandy sediment) with the potential to locally process a volume of water equivalent to the water column within <1 day. Data from 1991–2002 at one site suggest that the area-specific potential population filtration rate remains remarkably constant in time despite changes in population structure of M. arenaria. The related impact on pore water exchange within the permeable sediment associated with the leakage of water from the gape of M. arenaria valves is discussed.Communicated by L. Hagerman, Helsingør     

Reduction in carbon flux in Mya arenaria caused by a spill of No. 6 fuel oil

Rates of respiration, assimilation and filtration have been determined on a monthly basis for two populations of Mya arenaria in Casco Bay, Maine (USA), one of which was heavily oiled by a spill of No. 6 fuel oil. Monthly estimates of carbon flow have been calculated from these data. The same general trends were seen in each population; small negative carbon flow in winter, large negative carbon flow during the spring; large positive carbon flow during summer. However, the oiled population gained carbon at only 50% of the rate seen in the unoiled population. This difference results from the uptake of hydrocarbons by the oiled population.Contribution No. 75009 to the Bigelow Laboratory.     

Effects of Lunatia heros predation on the population dynamics of Mya arenaria and Macoma balthica in Maine,USA

The interaction between the naticid snail predator Lunatia heros and 2 iteroparous, infaunal, intertidal bivalves was investigated in Lubec, Maine, USA. The Mya arenaria population consists primarily of young, small individuals. M. arenaria survivorship is low when young (3.5% yr^-1 for the first 5 yr), then increases. M. arenaria can attain a length of 60 mm, but it is susceptible to L. heros attack only until it is 30 mm long. It delays reproduction until it is 20 mm long (3.8 yr) and diverts its resources instead into rapid early growth (4.9 mm yr^-1 for the first 5 yr). The Macoma balthica population has a larger proportion of older individuals than does that of M. arenaria. Survivorship is higher for M. balthica than for M. arenaria (76.3% yr^-1 for the first 5 yr). Unlike M. arenaria, M. balthica attains a final length of only 25 mm and all sizes are susceptible to L. heros attack. M. balthica grows slowly (2.7 mm yr^-1 for the first 5 yr) and diverts its resources into earlier reproduction at a length of 10 mm (2.9 yr). These contrasting life-history patterns and the possible relationship between bivalve resource allocation and refuges from predation are discussed.     

Strong population differentiation of softshell clams (Mya arenaria) sampled across seven biogeographic marine ecoregions: possible selection and isolation by distance

Twenty-two Mya arenaria samples spanning seven marine ecoregions mostly situated in the Cold Temperate Northwest Atlantic (CTNA) biogeographic province were collected between 2001 and 2010 and genotyped at seven highly polymorphic microsatellite loci to test for population differentiation. Results showed strong regional differentiation with six genetic clusters: (1) Northern Gulf of St. Lawrence (GSL), (2) Magdalen Archipelago, (3) Southern GSL, (4) Lower Atlantic Canada, (5) US Coasts and (6) Northern Europe. Population structure was supported no matter the statistical approach and generally does not reflect the geographical limits of marine ecoregions. A latitudinal cline in allelic richness provides evidence for a northward post-glacial expansion range for this species. While geographical distance explains the genetic variation detected in southern CTNA, increased heterogeneity observed in northern CTNA can be explained by isolation by distance, marine landscaping and presumable selective processes acting at the Mar5 locus. Exclusion of Mar5 from analyses resulted in the detection of three genetic clusters instead of six.     

Application of a temperature-dependent von Bertalanffy growth model to bullhead (Cottus gobio)

The most studied and commonly applied model of fish growth is the von Bertalanffy model. However, this model does not take water temperature into account, which is one of the most important environmental factors affecting the life cycle of fish, as many physiological processes that determine growth, e.g. metabolic rate and oxygen supply, are directly influenced by temperature. In the present study we propose a version of the von Bertalanffy growth model that includes mean annual water temperatures by correlating the growth coefficient, k, explicitly and the asymptotic length, L_∞, implicitly to water temperature. All relationships include parameters with an obvious biological relevance that makes them easier to identify. The model is used to fit growth data of bullhead (Cottus gobio) at different locations in the Bez River network (Drme, France). We show that temperature explains much of the growth variability at the different sampling sites of the network.     

The ecological niche of Daphnia magna characterized using population growth rate

The concept of an organism's niche is central to ecological theory, but an operational definition is needed that allows both its experimental delineation and interpretation of field distributions of the species. Here we use population growth rate (hereafter, pgr) to define the niche as the set of points in niche space where pgr > 0. If there are just two axes to the niche space, their relationship to pgr can be pictured as a contour map in which pgr varies along the axes in the same way that the height of land above sea level varies with latitude and longitude. In laboratory experiments we measured the pgr of Daphnia magna over a grid of values of pH and Ca2+, and so defined its "laboratory niche" in pH-Ca2+ space. The position of the laboratory niche boundary suggests that population persistence is only possible above 0.5 mg Ca2+/L and between pH 5.75 and pH 9, though more Ca2+ is needed at lower pH values. To see how well the measured niche predicts the field distribution of D. magna, we examined relevant field data from 422 sites in England and Wales. Of the 58 colonized water bodies, 56 lay within the laboratory niche. Very few of the sites near the niche boundary were colonized, probably because pgr there is so low that populations are vulnerable to extinction by other factors. Our study shows how the niche can be quantified and used to predict field distributions successfully.     

Influence of various concentrations of orthophosphate on the division rate of an estuarine benthic diatom,Navicula arenaria,in culture

A hydrolysis procedure along with a high-pressure liquid chromatographic procedure is given enabling simple and reliable thymine determinations in the nanogram range in different fractions of sea-water samples taken from three different locations in the Northern Adriatic Sea. The levels corresponded to 1–3 g DNA per liter. From total polyanionic thymine, which had been precipitated as the cetyltrimethylammonium salt, the highest percentage was linked to the particulate fraction, with a definite subsurface minimum at 10 to 15 m. There was a corresponding maximum of a high molecular non-particulate thymine-containing fraction at the corresponding depth. From the bottom at 30 m upwards to about 20 m, a low molecular thymine-containing material has been found. Remarkably these basic features were common to all three locations, one of which was supposed to be in clean water, one near a thickly settled, touristic area, and the other in front of a large river delta coming from industrial hinterland.     

Tissue distribution and excretion of 99mTc-disofenin in three marine species: Pleuronectes americanus (winter flounder), Homarus americanus (lobster), and Mya arenaria (soft-shell clam)

To determine the pharmacokinetics of a small lipophilic molecule in vivo, the distribution and accumulation of ^99mTc-radiolabelled disofenin (diisopropylacetanilide iminodiacetic acid) were traced during 1991–1992 by scintigraphy and gamma well counting in winter flounder (Pleuronectes americanus collected from Boston Harbor and Long Island Sound in 1992), lobsters (Homarus americanus collected from Massachusetts Bay in 1991), and soft-shell clams (Mya arenaria purchased in 1991). The agent was distributed throughout the bodies of lobsters within 12 s, throughout flounder within 40 s, and throughout clams within 2 min. It was concentrated most strongly by the liver of flounder, which contained 61.2±7.8% of the injected dose within 1 h of injection, and by the lobster hepatopancreas. Accumulation also occurred in the flounder kidney, lobster antennal glands, and the kidney and pericardial glands of clams. The compound was rapidly excreted from the flounder liver into the gall bladder, and from the lobster hepatopancreas into the stomach. The data suggest its excretion from the lobster antennal glands and clam kidneys. The rate of clearance of disofenin from the body varied among species: 99±2.1% of the initial dose remained in flounder sampled 16 to 24 h after injection, compared to 80.5±7% remaining in the lobster after 15 h, and 87.4±5.9% remaining in clams after 27 h. The clearance rates in flounder and lobster are considered to be minimum values because of the lack of gut activity in unfed individuals. Overall, these in vivo tracer studies establish the utility of scintigraphy for assessing the uptake and excretion of a lipid soluble compound in different taxa, and may be applicable for evaluating disease and/or environmental effects on organ function in marine animals.     

Gill pump characteristics of the soft clamMya arenaria

Pumping rates in the soft clamMya arenaria, collected in June 1987 in the Great Belt, Denmark, were determined as rates at which clams cleared suspensions of algae,Dunaliella marina. The frictional resistance of the siphons to water flow was estimated by studying the effect of excision of the siphons at the base on the rate of water pumping. The frictional resistance was also calculated from the Poiseuille equation. Excision of the siphons had no measurable effect on the pumping rate, and calculations indicated pressure losses ranging between 0.3 to 1.2 mm H₂O. This is consistent with the conception that the capacity of filter feeding bivalves to process large amounts of water depends upon a low resistance to water flow in the siphons.     

Disease progression and mortality in neoplasticMya arenaria in the field

Four 6-mo mark-and-recapture experiments conducted in Long Island Sound, USA, from 1988 to 1990, involving approximately 2250 individual observations, demonstrated that under natural conditions significantly higher mortality (p0.001, chi-square test) occurred amongMya arenaria (L.) with hematopoietic neoplasia than those diagnosed as non-neoplastic. Using a blood-screening technique, the clams were diagnosed and placed in one of three diagnostic groups based on the severity of the disease (the percentage neoplastic cells per total number of blood cells): non-neoplastic (NN), 0%; low-severity neoplastic (LSN), < 50%; high-severity neoplastic (HSN), > 50%. Mortality of those clams initially diagnosed as HSN ranged from 48% to 78%, depending on the test period, as compared to 3% to 21% for the non-neoplastic. Mortality in the LSN treatment varied from 8% to 34%. Both progression and remission were evident in clams at all stages of the disease. Mortality and rates of progression and remission in individuals appeared to be linked to water temperatures. Differential mortality may be responsible for the apparent seasonal cycle of prevalence in populations.     

Microgamete formation and the growth rate of Tintinnopsis beroidea

Microgametes have been detected for a species of Tintinnida for the first time. Apparently this method of sexual reproduction occurs rather infrequently in nature, whereas it is the predominant sexual process in vitro. Culturing conditions and the maintenance medium undoubtedly have a profound influence on microgamete appearance. The rate of division of Tintinnopsis beroidea is related to the degree of sexuality of the cells. Newly isolated cells have a doubling time of 0.8 to 1.1 day at an optimum ratio of food: protozoa. The new cultures have a low incidence of microgamete production.This work was supported by a contract with the U.S. Atomic Energy Commission, reference number NYO-3658-29.     

Effect of inorganic phosphorus on the growth rate of diatoms

The effect is studied of different inorganic phosphorus concentrations on changes in growth rates of 7 diatom species isolated from the plankton of the Black Sea. All species examined increase their cell-division rate with increasing phosphorus concentration in the medium. The phosphorus concentrations have been determined above which division rate is not limited by phosphorus content in the medium. The non-limiting concentration amounts to V/V _m =0.9. In the species studied, non-limiting concentrations ranged from 1 to 30 g P/1. The highest values were obtained for relatively large-sized species. The ratio of cell surface to volume tended to be inversely related to the growth-rate-limiting concentration. Minimal values of phosphorus content in cells have been calculated to range from 0.6 to 4.0·10^–17 g.at–P/^–3. Based on a comparison of phosphate levels in the Black Sea with experimentally-derived rate-limiting concentrations, it is concluded that phosphorus does not limit the reproduction rate of phytoplankton in the more productive regions of the Black Sea or in the lower strata of the euphotic zone.     

Genetics of larvae and spat growth rate in the oyster Crassostrea virginica

The heritability of oyster (Crassostrea virginica) larval growth rate was estimated to be in the range of 0.25 to 0.50 and a significant part of this genetic variation is of the additive type. Larval growth rate and spat growth rate were found to be highly correlated. These results suggest that a selection program for faster growing larvae and spat would be successful.     

Environment-specific elasticity and sensitivity analysis of the stochastic growth rate

For matrix population models, analyses of how sensitive the population growth rate is to changes in vital rates (i.e. perturbations) are important for studies of life history evolution as well as for management and conservation of threatened species. There are two types of sensitivity analyses corresponding to absolute (sensitivity) or relative (elasticity) changes in the vital rates and both types can be applied to both deterministic and stochastic matrix population models. To date, most empirical studies of elasticity and sensitivity of the stochastic growth rate have examined the response to perturbations in the vital rates in a complete set of possible environments. However, it is often of interest to examine the response to perturbations occurring in only a subset of the possible environments. This has been done for periodic time-varying models elsewhere, but here we describe a recently published method for calculating the environment-specific sensitivity and elasticity of the stochastic growth rate and apply this method to data. These environment-specific perturbation analyses provide a logical way of dividing the sensitivity and elasticity among the environments. They give important insight into the selection regime in different environments and can provide valuable information for making management decisions and management evaluations in stochastic environments.     

Genetic and environmental effects on the growth rate of Littorina saxatilis

Transfer experiments with two morphs of Littorina saxatilis Olivi (=L. rudis) typically inhabiting exposed and sheltered localities, showed a between-morph difference in shell growth in the same type of habitat, and a withinmorph difference between exposed and sheltered environments. The former indicates a genetic difference between the two morphs, although growth rate has an environmental component as shown by the latter. Juvenile snails of the exposed morph were on average slightly larger than sheltered morph juveniles on hatching, but at 20 wk, when raised in identical environments, the sheltered morph juveniles had grown significantly larger than the exposed ones. A rise in temperature from 5° to 10°C enhanced growth rate for snails raised in the laboratory. Temperature alone could not however explain increased growth during the spring and summer in natural populations.     

A new model for the CBL growth based on the turbulent kinetic energy equation

Starting from the evolution equation for the turbulent energy density spectrum (EDS), we develop a new model for the growth of the Convective boundary layer (CBL). We apply dimensional analysis to parameterize the unknown inertial transport and convective source term in the dynamic equation for the three-dimensional (3-D) spectrum and solve the 3-D EDS equation. The one-dimensional vertical spectrum is derived from the 3-D spectrum, employing a weight function. This allows us to select the magnitude of the vertical spectral component for the construction of the growing 3-D EDS. Furthermore, we employ the vertical component of the energy spectrum to calculate the eddy diffusivity (required in dispersion models). Currently there are no available experimental data to directly verify our EDS model.