Adult Clams Research Articles

Growth of Asiatic clams (Corbicula sp.) during and after long-term zinc exposure in field-located and laboratory artificial streams

Juvenile and adult Asiatic clams were exposed to 0.025-1.0 mg Zn/L for 30 days in artificial stream systems in an outdoor field laboratory and formal laboratory setting. All exposures (≧0.050 mg/L), except 0.025 mg/L, significantly reduced total weight gain between days 20 to 30 in the field-laboratory experiments. Laboratory exposures yielded little growth information as nutritional needs of the clam were not adequately satisfied; therefore, further research was confined to the field location. Exposures to 1.0 mg/L resulted in 10-50% mortality by day 30 in outdoor artificial streams. Significant increases in tissue water content of Zn-exposed clams indicated tissue degradation or osmoregulatory impairment. Bioaccumulation of Zn occurred at all levels of exposure and reflected growth inhibition at the levels tested. The maximum accumulation occurred in 1.0 mg/L treated clams (2000 Μg Zn/g dry weight). Controls varied consistently around 200 Μg Zn/g dry weight. When clams exposed to Zn (0.050-1.0 mg/L) were removed from exposure to control streams, Zn was completely depurated in 17 days with a concomitant return to normal growth patterns. Clams from the higher Zn exposures (0.50 and 1.0 mg/L) remained significantly different from controls due to earlier growth inhibition by Zn.Corbicula is a sensitive indicator of Zn stress at levels that are currently considered protective of aquatic life.

Uptake of Chrysotile Asbestos Fibers Alters Growth and Reproduction of Asiatic Clams

The effects of chrysotile asbestos on siphoning activity, shell and tissue growth, fiber uptake, and gill ultrastructure in adult Asiatic clams (Corbicula sp.) and on larval release and mortality patterns from reproductively active adults were evaluated in 96-h to 30-d experiments at 0–108 fibers/L. Adult siphoning activity was significantly (α = 0.05) depressed in 96-h asbestos exposures when no food was offered or after 30 d when food was available. Shell growth was significantly inhibited in accordance with reduced siphoning. Corbicula exposed to 108 fibers/L accumulated 69.1 fibers/mg dry weight if food was offered. Fiber uptake was not observed at lower concentrations in 96-h or 30-d tests. Adult clams exposed to 108 fibers/L for 30 d accumulated 147.3 and 903.7 fibers/mg in gill and viscera, respectively. Gill tissue was significantly altered at 108 fibers/L and fibers were observed in gill locules and in ctenidial tissue. Fiber dimension analysis suggested that small, thin fibers were preferentially accumulated by both gill and visceral tissues. Significant increases in mortality of larvae exposed to asbestos and decreases in larvae released per milligram of adult dry weight were observed in reproductive adults exposed to asbestos at 104–108 fibers/L. Corbicula is an efficient accumulator of chrysotile asbestos and may be considered for use as an indicator of asbestos contamination.

Long-term variations in cation content of two populations of adult marine clam (Tapes decussatus L. and T. philippinarum) reared in a common habitat

Abstract 1. 1. The levels of four major cations, Na+, K+, Mg2+ and Ca2+ were measured using flame spectrophotometry over a 16-month period in two populations of adult marine clam reared in a common habitat. 2. 2. The variations in absolute and relative values of Na+ and Mg2+ were virtually identical within each species; the relative values showed a marked increase during the period of negative energy balance previously reported, even when the external salinity decreased. 3. 3. Calcium levels showed very irregular long-term variations, reflecting its multiple roles as a metabolic, osmotic and structural element. 4. 4. A close relationship was observed between the levels of K+ and organic constituents, especially glycogen. 5. 5. An adaptive benefit of this relationship is postulated.

Seasonal variations in the fatty acids of the triacylglycerols and phospholipids of two populations of adult clam (Tapes decussatus L. and T. philippinarum) reared in a common habitat

1.1. Seasonal variations in fatty acid composition of the triacylglycerols and phospholipids of an indigenous and an introduced clam species reared in a common habitat were analyzed using gas-liquid capillary column chromatography.2.2. Despite different geographical origins, the fatty acid spectra of the two related species were quite similar.3.3. In both species the fatty acids of the triacylglycerol fraction, but not the phospholipid fraction, showed clear seasonal variation corresponding to the annual temperature cycle and not to reproductive activity.4.4. It is argued that such variations are related to the diet and are not endogenous.

Interactions between functional groups in soft-substrata: Do species differences matter?

Interactions of two tubicolous, deposit-feeding polychaetes, Clymenella torquata (Leidy) and Polydora ligni Webster, with a filter-feeding bivalve, Gemma gemma (Totten), were examined to test the functional group hypothesis that small, filter-feeding bivalves with large young should attain high densities with tube-builders of any trophic mode because the large young escape predation by tube-builders. The prediction was not supported by Polydora and Gemma, since the two species have not been reported to coexist in high densities in nature. In laboratory experiments, Polydora reduced recruitment and adult survival of Gemma relative to a control. Polydora preyed on juvenile clams and reduced the time which adult clams had their siphons in the feeding position, relative to a control. For Clymenella and Gemma, the functional group hypothesis made the correct prediction (i.e. the two species are reported to coexist in high densities in nature), but for the wrong reason. The size of Gemma's offspring is not related to the intensity of Clymenella predation. Clymenella does not ingest Gemma since the worm does not usually feed from the zone occupied by the clam. In contrast to Polydora, Clymenella did not reduce the time which clams fully extend and open their siphons relative to a control. In laboratory experiments Clymenella increased adult bivalve growth, survival after one year, and recruit size after one month. Clam life history characteristics were similar in the Clymenella and Clymenella plus Polydora treatments because the number of surviving Polydora was reduced by a negative interaction with Clymenella. The tube-builders had different effects on the filter-feeder, Gemma, because these tube-building species differ in feeding position, diet and behavior. Thus, the functional group hypothesis was too general to predict and explain the species interactions and distributions.

Seasonal variations in condition, reproductive activity, and gross biochemical composition of two species of adult clam reared in a common habitat: Tapes decussatus L. (Jeffreys) and Tapes philippinarum (Adams & Reeve)

The condition, reproductive activity, and gross biochemical composition of an indigenous and an introduced adult clam population raised in acommon habitat of the French Atlantic coast were examined over a 74-wk period. The indigenous species, Tapes decussatus L. (Jeffreys) and the introduced species, T. philippinarum (Adams & Reeve) were raised together on the south Finistère coast of Brittany. The gross biochemical composition of a standard animal of each population was significantly correlated with the population condition indices. During the winter, no reproductive activity was observed in either population, and the contribution of protein, glycogen, and lipids to the maintenance energy was calculated. Protein formed the main reserve, while lipids contributed as much as glycogen in T. decussatus, and twice as much in T. philippinarum. Although some species differences were noted in the mean levels of biochemical components, the overall seasonal variations were similar in both populations.

Seasonal variations of the major lipid classes in relation to the reproductive activity of two species of clams raised in a common habitat: Tapes decussatus L. (Jeffreys, 1863) and T. philippinarum (Adams & Reeve, 1850)

The relative and absolute levels of four major lipid classes in an indigenous and an introduced adult clam population raised in a common habitat were determined over a 74-wk period. The standard animal of each population contained a low and stable amount of the fraction containing wax esters, hydrocarbons, and sterol esters. The absolute levels of triacylglycerols and phospholipids closely followed the indices of reproductive activity. Following the summer spawning a severe negative energy balance was observed throughout the winter. During this period, both triacylglycerols and phospholipid contributed to the maintenance energy, although the phospholipids' contribution was greater in both populations. A comparison of the seasonal variations of absolute and relative values underscores the advantages of absolute values in the calculation of lipid class levels. Although some specific differences were found in mean lipid class levels, the overall seasonal variations of the lipid classes were similar in both populations.

Crab Response to Prey Density Can Result in Density-Dependent Mortality of Clams

Field experiments involving recovery of marked clams showed that even adult native littleneck clams (Protothaca staminea) could suffer high mortality to cancrid crabs. The mortality rate increased with clam density, suggesting that these crabs preferentially forage in areas of higher prey density. Acoustic telemetry showed that at least one of the crabs, Cancer productus, is sufficiently mobile to search large areas while foraging. This is important for understanding the effects that these large, mobile predators have on the distribution and the abundance of their prey and may explain the high incidence of crab predation seen in mariculture operations where the density of clams is artificially raised.

The toxicity of copper to the adult and early life stages of the freshwater clam,Corbicula manilensis

The copper sensitivity of adult and larval stages of the freshwater clamCorbicula manilensis was evaluated. In addition, copper concentrations were determined in adult clams exposed for 4 to 10 weeks to copper in a high-volume, flow-through bioassay. All bioassay systems utilized water that was low in total hardness and alkalinity. The response of the clams to copper depended on life stage. Copper sensitivity of larvae decreased markedly in successive developmental stages. LC5024's of veliger and juvenile larvae were 28 and 600 μg Cu/L, respectively. The mortality of trochophore larvae exposed to 10 μg Cu/L for one hr was 91.5%. The sensitivity to copper decreased with increased amounts of larval shell deposition. Adult clams were resistant to copper; the LC5096 was greater than 2,600 μg Cu/L. By comparison, the incipient lethal concentration (ILC, was lowless than 10 μg Cu/L. Adult clams accumulated more copper as concentrations in the water increased. Evidence was obtained for copper loss near or at death. Labile and total copper, as well as the coppercomplexing capacity, in the bioassay water were determined; the majority of copper was present as labile species. Toxicity was related to the quantities of labile copper in the water.

Effects of particle concentration and season on the filtration rates of the freshwater clam, Sphaerium striatinum Lamarck (Bivalvia: Pisidiidae)

The effects of particle concentration and season on the filtration rates of the freshwater clamSphaerium striatinum Lamarck were assessed by measuring clearance rates of small (2.02 µm) latex beads from dilute suspensions. Filtration rates decreased as particle concentration increased over a range of 2–64 mg 1−1, with rates decreasing in similar proportion for clams of all sizes. For a 1-mg clam, rates decreased from approximately 8.4 to 0.57 ml clam−1 h−1. Seasonal filtration rates for adult clams peaked during periods of greatest reproduction. The patterns for smaller clams are similar, though proportional changes in filtration rates differ for various sizes of clams.

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

The Importance of Predation and Intra‐ and Interspecific Competition in the Population Biology of Two Infaunal Suspension‐Feeding Bivalves, Protothaca staminea and Chione undatella

Effects of a crude oil and an oil dispersant (Corexit 9527) on populations of the littleneck clam ( protothaca staminea)

Field and laboratory experiments were carried out to investigate the effects of Alberta crude oil and an oil dispersant (Corexit 9527) on the larval settlement, survival, siphon activities and behaviour of the littleneck clam (Protothaca staminea). Corexit 9527 was much more toxic than crude oil, and the highest toxicity was obtained when Corexit 9527 was mixed with crude oil. Siphon activities were impaired and abnormal behaviour was exhibited when adult clams were treated with 100 ppm Corexit 9527, 1000 ppm crude oil or a combination of both. Larval settlement was not affected when the substratum was treated with 1000ppm crude oil but was retarded when the substratum was treated with a mixture of 1000 ppm oil and 100 ppm Corexit 9527. Gas chromatograms also showed that the retention time and depth of penetration of hydrocarbons in the substratum was increased when Corexit 9527 was used with crude oil.

Northern New England's threatened soft-shell clam populations

Commercial exhaustion of soft-shell clam,Mya arenaria, had become the fate of many potentially productive clamming areas along the coasts of Massachusetts, New Hampshire, and southern Maine. Investigations of a particularly severe case of soft-shell clam stock depletion in Hampton-Seabrook estuary, New Hampshire, indicated that by 1976 human diggers had removed approximately 87% of the adult clam resource that had existed in 1971. Meanwhile, circumstantial evidence strongly implicated the green crab,Carcinus maenas, as responsible for successive stock recruitment failures, these crabs having consumed most of the young seed clams before they could grow to harvestable size. In 1976, this apparent population imbalance may have been at least partly redressed by a prodigious spatfall, resulting in a massive and widespread reseeding of many flats along the northern New England coast. Spat, or seed clam, densities of up to 1,700 individuals per square foot, over areas of several acres, have been observed. Those clamming areas where aggressive predator control programs had been instituted exhibited the most favorable response in terms of seed clam survival and growth. Evidence also indicated that crowding in thickly seeded portions of the clam flats inhibited shell growth.

Experimental cultivation of Tapes japonica (Deshayes) (Bivalvia: Veneridae) in an artificial upwelling culture system

Growth and reproductive characteristics of Tapes japonica (Deshayes) were investigated in a system using artificially upwelled deep-sea water as a culture medium. Three successive generations of Tapes were reared on combinations of three planktonic diatoms: Chaetoceros curvisetus, Bellerochea polymorpha and Thalassiosira pseudonana. Market-size adults (38-mm shell length) were obtained in 13 months from post-set juveniles, and in 10 months from the 5-mm stage. Animal densities at 38 mm were 1 775 and 1 345 clams/m 2 for first and second generations, with survival rates of 64 and 63%, respectively. Ripe gonads were found in adult clams during much of the year. Spawning was readily induced in the hatchery and larvae metamorphosed in 2–3 weeks. Post-set survival rates of 52 and 84.5% were recorded. Juvenile clams (6.5-mm shell length) were fed Chaetoceros and Bellerochea and an unidentified cryptophyte flagellate (designated S-1) in seven different unialgal and mixed-algal diets. The monoculture diets produced slowest growth in clams after 5 weeks, yielding a 7.6-fold average increase in wet meat weight and an average length of 15-mm. The four mixed diets showed better growth as a group, producing a 12.6-fold average increase in wet meat weight. Although variation in growth on the mixed diets was small, the Chaetoceros + S-1 diet gave the best yield for the total number of algal cells provided. Clams fed this mixture averaged 16.7 mm in length and 0.22 g in weight after 5 weeks. This was the best wet meat weight gain of all groups.

The glochidia of certain Unionidae (Mollusca) in Nova Scotia and their fish hosts.

Morphological and morphometric comparisons among adult and glochidial unionids from two Nova Scotian locations showed that Anodonta implicata, A. cataracta cataracta, A. c. fragilis, Elliptio complanatus, and Lampsilis radiata radiata were present. Gravidity studies suggested that fully developed glochidia occur from September to May in Anodonta marsupia, for only 5–6 weeks in June and July in E. complanatus, and perhaps at least from spring to early fall in L. r. radiata. Seven of 12 fish species sampled bore glochidia, which were identified in five host species by comparisons of their shapes and dimensions with those of glochidia from adult clams. Results were as follows: A. c. cataracta in Catostomus commersoni in June only, A. implicata or A. c. cataracta in Gasterosteus aculeatus in May and June, Anodonta sp. in Apeltes quadracus and Pungitius pungitius in June, and E. complanatus in Fundulus diaphanus in June and July. Thus, no relationships between gravidity periods of adult clams and infestation periods of their fish hosts by their glochidia were evident for species of Anodonta.

Occurrence of Gas-Bubble Disease in Three Species of Bivalve Molluscs

Gas-bubble disease was observed in adult oysters and hard clams held in heated running sea water during the winter. Heating the cold sea water in closed heat exchangers caused it to become supersaturated with atmospheric gases. Exposure of the animals to this water caused the formation of gas-filled conchiolin blisters on the valves of the oysters. Bubbles of gas were observed in the gill filaments of the oysters and clams and in the mantle tissue of the oysters. Any method, such as the use of baffles or an aerated head tank, that reduces the dissolved gas concentration in the water will help prevent the disease.

Self Righting by Tridacnid Clams

TRIDACNID clams can be divided into two distinct groups on the basis of whether they are physically fastened to the substrate. Of the six species comprising the family Tridacnidae1, Tridacna crocea, T. maxima and T. squamosa live byssally attached to dead coral, coral rubble or limestone during the whole of their adult lives. The other species, T. gigas, T. derasa and Hippopus hippopus, live byssally anchored as juveniles, but when approaching maturity their byssus glands atrophy, and the adult clams take up unattached existence on coral rubble or hard packed sand. This habitat difference is also expressed in the weight and morphology of their shells. The byssally attached species possess shell valves which are in most respects larger editions of those found in other bivalves (Fig. 1 A). The unattached clams, on the other hand, possess bizzare shells which are unusually massive resulting from a unique deposition of solid shell material within the cavities of the umbones (Fig. 1 B).

Lipids in the economy of marine invertebrates.

Lipids in the economy of marine invertebrates.

THE LOCALIZATION OF HEPARIN-LIKE BLOOD ANTICOAGULANT SUBSTANCES IN THE TISSUES OF SPISULA SOLIDISSIMA

1. A heparin-like blood anticoagulant has been isolated from the surf clam Spisula solidissima.2. The most potent preparation obtained had an anticoagulant activity of 130 U.S.P. heparin units per milligram and was derived from mantle tissue.3. Anticoagulant assays made on tryptic digests from various portions of the clam revealed that the mantle, gills and palps had about five times more anticoagulant activity per gram of tissue than the foot and adductor muscles. It was also found that the eggs of Spisula yield a high anticoagulant activity.4. Toluidine blue staining of sectioned eggs revealed metachromasia in the jelly coat, cortical region and nucleolus.5. In order to determine the origin of the anticoagulant from the adult clam, the results from anticoagulant assays made on digests of isolated portions of the mantle edge were compared with histologic observations concerning metachromasia. It was concluded that at least two substances with heparin activity are present in the mantle tissue. One of thes...

SEASONAL GONADAL CHANGES OF ADULT CLAMS, VENUS MERCENARIA (L.)

The literature on Pelecypoda mollusks contains but few accounts of systematic studies of the changes occurring in the gonads of an animal throughout the entire year. This phase of investigation of sexual phenomena in mollusks, though neglected so far, is, however, of considerable importance and interest because, if properly carried out, it could assist greatly in the understanding of the phenomena of change of sex in some forms or add to the knowledge of the alternation of sexual phases in others. Amemiya (1929) reported a very interesting case of sex change in the Japanese oyster, 0. gigas, which was previously considered dioecious. His method consisted of making a hole in the shell of an oyster and removing through it a small piece of gonad for determination of sex. Following this the oysters were placed in cages and returned to the water for a period of one year, at the end of which they were re-examined. Meanwhile, no samples were taken for histological studies to determine what cellular changes precede the reversal of sex. Nelson (1928) gave a more or less detailed description of changes occurring in the gonads of the adult 0. virginica from April until June, but did not continue his studies through the post-spawning time and season of hibernation. In other studies dealing with sexual phenomena of the genus Ostrea, a systematic description of changes occurring in the gonads of adult animals throughout the year is also lacking. This paper deals with the changes occurring in the gonads of adult clams (Venus mercenaria) at different seasons of the annual cycle. The animals were studied for three successive years. Samples for this study were collected at bi-weekly intervals from the clam beds located near Charles Island, Long Island Sound. The depth of the water over the beds was 8-12 feet at mean low water. Since the calendar's new year, occurring in the middle of winter, coincides with the prolonged period of the animal's inactivity, it is thought convenient in this study to consider the beginning of a new year from the ecological point of view, i.e., after the completion of