Large Clams Research Articles

Nutrition of the giant clam Tridacna gigas (L.) I. Contribution of filter feeding and photosynthates to respiration and growth

The total carbon requirements (growth + respiration) of the host tissues of the giant clam Tridacna gigas from Davies Reef on the Great Barrier reef were measured, and compared with rates with which nutrients were acquired from the two potential sources, translocated photosynthates (estimated from oxygen flux-CZAR method) and filter feeding. Results showed that the giant clam is an efficient utilizer of particulate organic matter available in reef waters (Davies Reef mean: 97 μg C·1 −1), retaining on average 75% of particles between 2 and 50 μm, and absorbing from them 54% of C. Clearance rates ( CR, 1·h −1) of clams were size dependent as defined by the function: CR = 1.85 W 0.58 (r 2 = 0.85, n = 56) . There are major differences between typical non-symbiotic bivalves and Tridacna gigas regarding the relative allocations of energy to respiration and growth. The proportion of carbon deposited in tissues relative to that respired is high in giant clams relative to completely heterotrophic bivalves. We conclude that autotrophy is the major source of carbon to this clam, potentially capable of satisfying all respiratory requirements of the host. However, the potential importance of heterotrophy to total energy needs of the host is also significant and changes with the size of clam. The spectacular rates of growth in this clam are such that filter feeding is able to provide 65% of the total carbon needed both for respiration and growth in small clams (100 mg dry tissue wt), whereas large clams (10 g) acquire only 34% of their carbon from this source.

The relationship between parasite load, crawling behaviour, and growth rate of Macoma balthica (L.) (Mollusca, Pelecypoda) from Hudson Bay, Canada

At ebb tide Macoma balthica makes crawling tracks on the intertidal sand flats near Churchill, Manitoba, on Hudson Bay. Clams from two tidal levels, mean low water and 1.0 m above mean low water, were sampled to compare the parasite load and growth rate of crawling versus buried Macoma. For each clam the number of trematode metacercariae present were counted and the growth rate was determined by the measurement of annual growth rings. Clams were infected by more metacercariae at the higher than at the lower tidal level, larger clams more than smaller ones and crawling clams more than buried ones. Increased exposure of the clams at the higher tidal level to shorebirds, the final host of the trematodes, is proposed as the reason for the difference in parasite load between the tide levels. High-tide clams (more parasitized) grew faster than low-tide ones (less parasitized), and crawlers (more parasitized) grew faster than the buried (less parasitized) clams. Enhanced somatic growth as a result of parasitic castration is proposed to be the most logical explanation to account for the faster growth of the parasitized clams.

The Size Selection of Clams by African Black Oystercatchers and Kelp Gulls

The selction of prey by two species of shore—dwelling birds was compared with the predictions of a simple optimal diet model. The preferences of African Black Oystercatchers (Haaematopus moquini) and Kelp Gulls (Larus dominicanus) for different size classes of the sand—burrowing bivalve Donax serra were examined. Gulls took only large clams, regardless of the availability of the different size classes. This preference is ascribed to the high energy expenditure required for gulls to open clam shells. Oystercatchers, which open bivalve shells relatively easily, took both small and large clams, even when large clams were abundant. The selection of small clams when large clams were abundant appears to have resulted the lack of discrimination of clam sizes by oystercatchers and the temporal segregation of availability of small and large clams.

Indirect effects of clam digging on the viability of soft-shell clams, Mya arenaria L.

A series of laboratory experiments was conducted to determine whether non-lethal burial or exposure on the sediment surface could alter the normal living depth of Mya arenaria in sand and mud. After 2 weeks, clams (∼ 3 to 7 cm shell length) which were buried under 1 to 15 cm of medium-fine sand were found deeper than the controls, whereas clams (∼ 1 to 7 cm length) which were exposed on sand (and had subsequently reburrowed) were able to re-establish their normal living depth. In contrast, clams (∼ 1 to 7 cm length) buried under 1 to 15 cm of mud attained their normal living depth within two weeks, but exposed clams (∼ 1 to 7 cm length) reburrowed to abnornally shallow depths. An increased likelihood of predation at shallow sediment depths was compounded by the 60% slower reburrowing speed of exposed clams in mud than in sand. An additional experiment determined the approximate depth of burial under which at least 50% of a laboratory clam population could survive (LD 50). For small (< 3 cm in shell length), mid-size (3 to 5 cm) and large (> 5 cm) clams in sand, LD 50 values were < 75 cm, > 75 cm and between 50 and 75 cm, respectively. In mud, the LD 50 of clams < 5 cm in length was < 25 cm, and between 25 and 50 cm for clams ≥ 5 cm in length. It was concluded that the indirect mortality level associated with commercial and recreational harvesting will be much greater on intertidal mudflats than on sandflats.

Se uptake and accumulation in marine phytoplankton and transfer of se to the clam Puditapes philippnarum

Se uptake and accumulation in marine phytoplankton and the transfer of Se to the clam Puditapes philippnarum was studied. The accumulation of Se in three marine diatoms, Skeletonema costatum, Phaeodactylum tricornutum and Chaetoceros muelleri was rapid and concentration factors were generally > 10 4. The accumulation of 75Se by the clam P. philippnarum was mainly from Se-labelled food (phytoplankton), with lesser amounts being accumulated directly from seawater. The clam assimilated Se from ingested phytoplankton with an assimilation coefficient of over 50%. When Se was accumulated via food, the largest amount of Se was in the soft tissues in the following order: viscera > gills > gonads > mantle > muscle. When Se accumulation was via seawater, Se was found mainly in or on the shell. The excretion kinetics of Se revealed two compartments. The short-lived compartment had a biological half-time of 8 days for small clams and 13 days for large clams, while for the long-lived compartment it was about 52 days for clams of both sizes.

Dynamics of Filter-Feeding in Musculium transversum (Bivalvia:Sphaeriidae)

Filtration rates of Musculium transversum from Brown's Lake, Mississippi, were measured at suspended particle concentrations spanning the yearly ambient range. Filtration rates for adult clams increased as particle concentrations increased from 5 to 26 mg/L, then decreased with further increases in particle (2-μm microspheres) concentration. Maximal filtration rates were observed at particle concentrations near the mean annual average (15.2 and 15.7 ml/hr at 18 and 26 mg/L, respectively). The effects of particle size and type on filtration rates were examined using microspheres of various sizes, natural suspended particles, and Chlorella at the mean ambient suspended particle concentration. Filtration rates were highest when measured with particle sizes most commonly encountered in the water column. There was also no difference in filtration rates measured with 5-μm microspheres and similar sized Chlorella. Musculium transversum could not retain particles less than 1 μm in size indicating that ciliary feeding structures act as a sieve with a minimum mesh size of approximately 1 μm. Pseudofeces were produced by all sizes of clams at particle concentrations greater than 26 mg/L and at particle sizes greater than 7 μm for newborn and medium sized clams and 11 μm for large clams. Thus morphological constraints on the gill limit the range of particle concentrations and sizes that can be effectively processed. Laboratory observations demonstrated the potential for deposit feeding in M. transversum in habitats that have rich organic substrates, low quantity or poor quality of suspended food, or seasonal variation in the abundance of suspended food.

Effect of Size-Selective Predation by Muskrats (Ondatra zebithicus) on a Population of Unionid Clams (Anodonta grandis simpsoniana)

SUMMARY (1) The effect of size-selective predation by muskrats on the population size, sizestructure, and growth of clams was evaluated in a small lake in central Alberta. Clam shells were collected at regular intervals over 1 year from muskrat middens found along the shoreline of the lake. The number, biomass, size distribution, and age distribution of clams eaten were compared with the number, biomass, and age and size distributions of clams in the lake. (2) Muskrats ate almost 37000 clams, or 3% of the population in the study area in I year. When expressed as biomass, muskrats ate 677 kg of clams, which was equivalent to 5 8% of the biomass and 31% of the annual production of clams in the study area. (3) Muskrat predation was highly size-selective-86% of the clams eaten were > 55 mm long compared to 37% for clams in the lake-and had a strong effect on the size structure of the clam population. When all age-classes were combined, the biomass of clams > 70 mm eaten exceeded the annual production by an amount equivalent to 9 5% of the estimated biomass in the lake. Muskrats ate the fastest growing clams between 3 and 9 years old. Mean length at annulus did not increase for clams older than age-8 in the lake. The biomass of large clams in the lake will therefore decline if the observed predation continues. (4) Muskrats ate a large fraction of the reproductive output (glochidia) of the largest clams. Only 6% of the glochidia of clams 70 mm long was eaten. Genetic selection for slow growth has not occurred.

Diet Selection and Optimization by Northwestern Crows Feeding on Japanese Littleneck Clams

Northwestern Crows {Corvus caurinus) feed extensively on littleneck clams {Venerupis japonica) despite the high cost in time and energy incurred in digging up the clams, opening them, and then extracting the edible parts. Casual observation also indicated that the crows fed preferentially on the larger clams. The purpose of this study was to quantify this apparent selectivity, to determine the energetics of the foraging process, and to compare the birds' net energy gains with the gains predicted by a random encounter model. The overall length of clams in the beach ranged from 10.0 to 43.0 mm. All sizes broke equally easily {X = 1.7 drops per clam), but the time taken to extract the meat from broken clams increased with size. Despite this, net energy gain per unit of handling time was an increasing function of clam size. Foraging crows ate clams between 24.0 and 43.0 mm long. They also dug up but rejected clams ranging from 13.0 to 35.0 mm long. The lower limit ofthe crows' diet, taken as the size which was eaten 50% ofthe times encountered, was 29.0 mm. We calculated that a diet consisting of clams >28.5 mm long yielded the maximum possible rate of net energy gain. These data clearly show that crows not only feed selectively on large clams but that their selectivity results in a net energy intake rate close to the maximum attainable.

Life history variation in Pisidium (Bivalvia: Pisidiidae)

Intraspecific variation in the maximum shell length of Pisidium is small in comparison with variation in the life span of the clams, from 4 mo to 4 yr. The use of shell length as a measure of size is complicated by large intraspecific variation in the weight‐length relationship, a possible reflection of resource availability on the weight of the soft parts. Maximum embryo length is relatively constant (1 mm) in the majority of species but litter size is variable (1 to 40), generally increasing with parent size. The time of egg‐laying is determined by the size of the clam, season, and previous episode of reproduction, while the timing of the release of embryos, depending also on embryonic growth rate, is additionally affected by temperature and oxygen conditions. In brief, the maximum adult and embryo lengths are relatively conservative traits while growth rates vary by an order of magnitude.Reproductive effort, when measured by the ratio of litter weight to parent weight, may increase or decrease with parent length and age. Both semelparous and iteroparous populations are known in several species. We suggest that if maximum adult length can be reached by the first reproductive season (in a favourable environment) the population is semelparous, otherwise (in an unfavourable environment) the population is iteroparous. Gravid clams in semelparous populations continue to grow, and thus assimilation cannot be meaningfully partitioned into reproduction, somatic growth and maintenance.Along a depth gradient from 8 to 65 m, maximum and mature shell lengths, embryo length and litter size varies significantly in Pisidium conventus subpopulations not distinguishable electrophoretically. Large clams in deep water produce large embryos but small litters, which is contrary to the general trend of increasing litter size with parent length. Low food availability that decreases juvenile growth rate may restrict litter size in this case.

Vertical Distribution of Infauna in Sediments of a Subestuary of Central Chesapeake Bay

The vertical distribution of infauna was quantified in eight strata from 0–35 cm in sand and mud sediments of a lower mesohaline subestuary of Chesapeake Bay. Large numbers of small polychaetes, amphipods, and clams occurred in the upper 5 cm of both sediment types, whereas large clams (Macoma balthica in mud andMya arenaria in sand) extended down to 30 cm and comprised most of the biomass in their respective sediment types. There was extensive overlap of the species inhabiting both sediment types. Vertical stratification within and among species apparently reflected constraints on burrowing depth related to body size rather than resource partitioning among competitors. The maximal sediment penetration of 35 cm, which was exhibited byHeteromastus filiformis, was considerably less than the maximal penetration for deep burrowing species in some marine infaunal communities. Several species which burrowed deeper than 5 cm exhibited significant temporal shifts in their vertical distribution.

Hydrothermal Vent Animals: Distribution and Biology

Hydrothermal vent communities characterized by large clams, mussels, and vestimentiferan worms thrive on chemosynthetic microbial production. There are similarities in the animal distributions at vent communities from 20 degrees S to 46 degrees N on the Mid-Ocean Ridge in the Pacific Ocean and at cold sulfide seeps in the Gulf of Mexico. Vent communities, consisting of at least 16 previously unknown families of invertebrates, are at least 200 million years old. Since the life-span of a vent is only tens of years, the species survive by rapid growth and widespread dispersal of larvae with the subsequent colonization of new vents.

Growth Rates of the Asiatic Clam, Corbicula fluminea (Müller), in the Kanawha River, West Virginia

This study was designed to assess growth rates of Corbicula fluminea under summer and winter conditions. A total of 80 small C. fluminea individuals were segregated into three shell length classes based on initial shell length. Thirty clams were assigned to Class I (<10 mm); 25 to Class II (10 to 11.9 mm); and 25 to Class III (12 to 14 mm), and placed in separate cages in the Kanawha River at Marmet, West Virginia, for a 12 week period (16 July thru 7 October 1983) when mean water temperature was 26.6°C. 'Warm water' growth rates (length/weight) were: Class I, 0.95 mm/week and 0.27 gm/week; Class II, 0.86 mm/week and 0.29 gm/week; Class III, 0.80 mm/week and 0.30 gm/week. An additional 78 clams were assigned to the same shell length classes and maintained in the Kanawha River for a 12 week period (11 October 1983 through 3 January 1984) when mean water temperature was 10.3°C. Thirty-three clams were assigned to Class I; 30 to Class II; and 15 to Class III. 'Cold water' growth rates were: Class I, 0.09 mm/week and 0.009 gm/week; Class II, 0.08 mm/week and 0.013 gm/week. Class III clams were destroyed by a predator. Summer growth rates were approximately 10.7 times higher than winter growth rates based on length and 22-32 times higher based on weight. In addition, smaller clams had higher growth rates than larger clams.

Seasonal and Spatial Distribution of the Carolina Marsh Clam Polymesoda caroliniana (Bosc) in a Mississippi Tidal Marsh

The abundance of the marsh clamPolymesoda caroliniana at four stations on a Mississippi tidal marsh was followed from February 1977 through April 1978. The stations varied with respect to inundation time and vegetative cover. The largest population was found in an area flooded 12% of the year (136 individuals per m2) and in an area flooded 3.2% of the year (126 individuals per m2). However, the latter area contained no large clams (>25.5 mm). Smaller populations were found in the upper reaches of a tidal creek draining the marsh (68 individuals per m2) and in an area flooded 5.8% of the year (73 individuals per m2). The average abundance of the clams on the marsh was 100 per m2. At least three recruitment periods were apparent. In laboratory studies, clams larger than 15 mm survived longer than 30 days without water. Clams smaller than 12 mm survived less than 6 days without water. Several decapods (Callinectes sapidus, Uca longisignalis, andSesarma reticulatum) consumed clams smaller than 10 mm but were unable to eat larger clams under laboratory conditions.Polymesoda caroliniana may be important to the functioning of the marsh by removing large quantities of particulate matter from flooding water.

Observations on the behavior ofAsterias forbesifeeding onMercenaria mercenaria

Abstract The behavior of the sea star, Asterias forbesi, feeding on hard clams, Mercenaria mercenaria, was observed in large tanks with and without sand as a substrate for burial. The sea star captures clams by excavating them, apparently in a non-random fashion. This behavior is described. The seasonal feeding pattern of A. forbesi on buried clams was bimodal with peaks occurring in the spring and fall. Sea star digging effort (# pits/day/clam excavated during each monthly sample) varied with the average monthly temperature from Sept. 1977 to June, 1977. During March and April 1977, three day averages for number of sea star excavations varied with three day averages for the number of visible clam siphons. More clams were unearthed between the new moon and first quarter than between other phases of the moon. A. forbesi attempted to open clams either solitarily or in aggregation. Both processes depended on the realtive sizes of predator and prey. Large clams (5->7 cm length) were generally attacked in aggr...

Effects of Size and Temperature on Mud Crab, Panopeus herbstii, Predation on Hard Clams, Mercenaria mercenaria

Predation byPanopeus herbstii onMercenaria mercenaria was significantly affected by temperature, and the size of predators and prey items. LargerP. herbstii opened more clams and preyed more successfully on larger clams than did smaller crabs. Increase in seed clam size and decrease in water temperature significantly reduced predation. Clam size appeared to be more important than crab satiation in reducing predation rate. Planting larger seed clams in cooler months should help to improve clam survival by reducing the impact ofP. herbstii in culture operations.

Survey of the U.S. Atlantic Coast Surf Clam, Spisula solidissima, and Clam Products for Anisakine Nematodes and Hyperparasitic Protozoa

Surf clams, Spisula solidissima, and processed surf clam products (that may also contain meat of the mahogany clam, Artica islandica) were examined for their parasite content. Of 3,358 raw clams collected on the U.S. Atlantic Coast from July 1976 through September 1977, 771 (23%) contained ani- sakine nematodes classified as a Sulcascaris sp. Of the 1,696 recovered anisakine nematodes, 15 (<1%) had discernible numbers of spores of a protozoan, Urosporidium spisuli; this represented a large decrease in the hyperparasitism observed during the previous 3 yr. The average number of nematodes per 100 clams was 51. Small clams contained fewer nematodes than large clams, and there was no seasonal fluc- tuation of incidence, indicating that the nematodes persist and accumulate in the clams. Southern clams contained more nematodes than northern clams; this geographical distribution corresponded to the dis- tribution of sea turtles, Chelonia mydas and Caretta caretta, believed to be definitive hosts of the ani- sakine nematode. The nematode was found in all parts of the clam, and its numbers in the edible and nonedible portions of clams were similar. Although most clams showed no gross tissue reactions to the nematode, there was thickening of clam tissue surrounding approximately 60 recovered nematodes; 16 nematodes were in individual cysts of clam origin. In 226 portions of 100-g amounts of canned clams, 10 nematodes or nematode fragments were recovered from 3.5% of the portions; nine nematodes or fragments were recovered from five of 229 portions (2.2%) of 100-g amounts of frozen, breaded clams. These figures represent a decrease in nematode contamination of processed clam products from preceding years.

Ionophore-mediated calcium control of ciliary arrest in the fingernail clam, Musculium transversum

1. 1. Lateral cilia on the gill of the fingernail clam, Musculium transversum, normally beats with a metachronal rhythm. 2. 2. The metachronal rhythm is maintained in the presence of 10.0 mM calcium chloride (CaCl 2), 15 mM potassium chloride (KCl) or 15 mM NaCl. 3. 3. Lateral ciliary arrest occurred when the gill perfusion contained 10 mM CaCl 2 and 10 −5 M (small clams) or 10 −6 M (large clams) A23187 (a calcium ionophore). 4. 4. Lateral ciliary arrest is not produced in either CaCl 2 or ionophore and monovalent cations alone. 5. 5. Restoration of the metachronal rhythm results with superfusion of lateral cilia in KCl, CaCl 2 or NaCl alone. 6. 6. These data show the important role that intracellular Ca 2 + concentration has on the behavior of lateral cilia. The physiological significance seems to be the momentary or complete shut down of water currents under unfavorable environmental conditions.

Size-Dependent Variation in the Evasive Behaviour of the Bivalve Mollusc Spisula Solidissima

ABSTRACT The evasive jump response of Spisula can be elicited by contact of the siphons with the tube feet of a starfish (Asterias forbesi). The level of responsiveness varies with the size of the individual clam; small clams (2·0–5·0 cm) being very responsive, large clams (12·0–18·0 cm) being totally unresponsive. The cell bodies of touch-sensitive neurones subserving the siphons are located in the visceral ganglion. The mean area of the receptive fields of these neurones in small clams is 33·8 mm2 and in large clams is 9·7 mm2. In small clams the large proportion of the total siphon surface innervated by single touch-sensitive neurones results in considerable overlap of receptive fields. As a result of this overlap, numerous touch-sensitive neurones are activated by a point stimulus. The variation in jump responsiveness of large and small clams is correlated with the size of the receptive fields of touch-sensitive neurones.

Maximum tension developed by the posterior adductor muscle of the giant clam, Tridacna gigas (Linné)

1. 1. The isometric closing tension of the posterior adductor muscle of giant clams, Tridacna gigas (L.), was measured under natural conditions on reefs and under more controlled conditions aboard the R/V Alpha Helix. 2. 2. Active tension increased with muscle length up to the maximum in vivo length. 3. 3. Tensions per unit cross section of the adductor averaged 8·0 ± 1·1 kg/cm 2 at 120% minimal length (minimal length = length at full valve closure) when the cross section area is the area at this length. If the tension is calculated with respect to the cross section area at minimal length the value becomes 6·7 ± 0·9 kg/cm 2. The values were relatively constant for clams ranging in size from 6 to 212 kg total weight. 4. 4. The total tension developed by the posterior adductor in large clams was well over 500 kg.

Some Factors Influencing Reburrowing Activity of Soft-Shell Clam, Mya arenaria

Three size-groups of soft-shell clams,Mya arenaria, averaging 45, 60, and 74 mm in shell length were placed in aquaria and their rate of reburrowing measured. The substrate in each aquarium consisted of sand particles: (I) less than 0.5 mm, (II) 0.5 to 1 mm, (III) 1 to 2 mm, (IV) 2 to 4 mm, and (V) an equal combination of the previous 4 sizes. New specimens were tested at every 5 C rise or fall in ambient water temperature and observations were made periodically for 48 hours. The three variables, water temperature, clam size, and sediment particle size were highly significant (1% level), in influencing clam reburial activities by the end of the second hour through the termination of the experiment 48 hours later. Optimum water temperatures for reburrowing were between 8.8 and 21 C. After 48 hours, 62% of the small, 39% of the medium, and 21% of the large clams had reburrowed in all experimental tests combined. The aquarium with less than 0.5 mm substrate particle size had the greatest percentage of reburrowed clams of each size. As the particle size increased, progressively less reburrowing took place. Most reburrowing took place between 4 and 8 hours after the start of the experiment.