Live Clams Research Articles

HISTORICAL EVIDENCE FOR HABITAT CONVERSION AND LOCAL POPULATION DECLINE IN A NEW ZEALAND FJORD

Although direct links between habitat conversion and human activities are often apparent, their causal mechanisms may be less obvious. We identified historic salinity change, attributed to freshwater input from a hydroelectric power plant, as a potential mechanism of intertidal habitat conversion and severe local decline of the New Zealand littleneck clam (Austrovenus stutchburyi) in Doubtful Sound, New Zealand. Live clams were abundant at sites distant from the power plant with relatively unaltered salinity regimes, and were absent from the inner fjord near the power plant outflow. Remnant shells indicate past habitation by A. stutchburyi at inner fjord sites. Historic salinity conditions inferred from oxygen isotope ratios in shell carbonates confirm that salinity previously reached higher values in the inner fjord, and that A. stutchburyi probably has not inhabited that area since salinity was at pre‐power‐plant levels. A laboratory experiment showed that A. stutchburyi from Doubtful Sound have a high tolerance for low salinity conditions, but that hyposaline conditions become lethal after extended exposure (37‐day LC50 = 2.5). In situ transplant experiments demonstrated that present salinity conditions in the inner reaches of Doubtful Sound are lethal to this species. Our findings suggest that the increased freshwater input maintained by the power plant has converted the habitat in the inner reaches of Doubtful Sound to one with sustained low salinity unsuitable for the survival of A. stutchburyi.

Nitrogenous Compound Changes in Live, Stored Clam, Tapes decussatus

The influence of emersion and storage temperature (5, 10, and 20°C) on survival and metabolism of non-protein nitrogenous compounds of wild harvest clams, Tapes decussatus, were assessed under laboratory conditions. The clams showed a temperature dependence of emersion tolerance with the highest survival at 10°C (LT 50 = 16 d) and the least survival at 20°C (LT50 = 5 d). Ammonia and trimethylamine (TMA) levels in the mantle cavity fluids of emersed clams, at all temperatures, increased exponentially (r2 > 0.8 in all cases) which implies a steep rise in the production of these nitrogenous compounds following an extended period of emersion (> 5 d in all cases). Tissue levels of TMA and total volatile bases (TVB) in the live clams showed a similar pattern of increase as a function of emersion duration and attained final values comparable to those which, on the basis of sensory analysis, would indicate that fish fillets were spoiled (> 12 mg TMA per 100 g tissue). Concomitantly, tissue trimethylamine oxide (TMAO) levels declined to undetectable values. At 10°C and 20°C, the mantle cavity fluid ammonia and TMA levels showed a strong correlation with tissue TVB and TMA concentrations (r = 0.91 and 0.92, respectively). It is suggested that, in such cases, mantle cavity fluid TVB/TMA analyses form a practical, non-destructive quality criterion for live-marketed clam.

Population characteristics of abundant bivalves (Mollusca, Vesicomyidae) at a sulphide-rich seafloor site near Lihir Island, Papua New Guinea

Extensive beds of sulphide-habitat-associated clams are present on the summit of Edison Seamount (1450 m depth) near Lihir Island, Papua New Guinea. These vesicomyids represent a new species. Imagery indicates that two major fields are several hundred metres in size. Four large grabs yielded over 270 live clams up to 23 cm in length plus many shells. The size structure of the populations suggests that settlement occurs in cohorts and that successful recruitment occurs mostly in areas with few adult clams. Dead juveniles were most abundant in the grabs with dense adults. Images from a towed camera sled included scales to allow density estimates that range up to 240 clams/m2(in small patches) with sizes averaging around 16.5 cm in length. A biometric relationship for length to wet mass allows calculation of estimates of biomass represented by clams measured in photographs. The average biomass value in Lihir clam beds is 13.3 kg/m2, with maximum values over 29 kg/m2(wet mass including shells). We compare these values with those of other studies that retrieved fewer specimens or imagery. We suggest that several overestimates populate the literature but that values around 30 kg/m2rival the biomass of intertidal bivalve beds.

A Social Cost-benefit Analysis of a Small-scale Clam Fishery in the Eastern Cape, South Africa

When a proposal was advanced in 1991 to harvest the wedge clam Donax serra in the Eastern Cape, South Africa, for commercial gain, it elicited a huge public outcry. In order to shed light on the issue, a social cost-benefit analysis (CBA), based on a biologically sustainable extraction rate of 100 ton of clams per year, was carried out on its commercial exploitation. Because fishery activities might exact a price on society in the form of negatively altering the quality of people's recreation experience in the area, as well as damage the aesthetic and ecological attributes of the beach system, such external effects were identified and valuated. Results from the CBA yielded positive net present values (NPV s) for project options involving live clams being sold on the export market (to Hong Kong) for R24.70 kg−1 and negative NPV s for domestic market options (Johannesburg and Cape Town), where the clam would be sold for R6.50 kg−1. Assuming a discount rate of 8%, the highest NPV was obtained for the scenario in which total production was sold on the foreign market and the firm rented facilities of an existing organization. The external cost was the single largest component of the cost of the fishery. The conclusion drawn is that the social benefit of the project exceeds the social cost – a conclusion which supports commercial exploitation of clam stocks along the St Francis Bay beach, but one which does not include the costs associated with policing.

Adding value to live, commercial size soft-shell clams ( Mya arenaria L.) in Maine, USA: results from repeated, small-scale, field impoundment trials

The soft-shell clam ( Mya arenaria L.) fishery in the state of Maine, USA, is worth $5–10 million annually and is primarily based on the sale of live individuals. More than 80% of the catch is sold for the “steamer clam” market that is highly seasonal due to supply and demand. Prices paid to harvesters for live clams throughout the year increases by as much as 70% during a 4-month period between early spring and late summer. If clams harvested in the spring could be held until late summer, a value-added product could be developed in this fishery. From April to August 1996, at an intertidal and subtidal location in eastern Maine, I tested whether it was biologically feasible to impound commercially harvested clams (shell length=44–75 mm) at densities between 720 and 850/m 2 using cages and nets (1.12 m 2) to protect animals from predators. Survival was 91.7% ( n=12) and 91.6% ( n=6) at the intertidal and subtidal site, respectively. There was no discernible shell growth during this period and there was no difference between initial and final clam weights. The methodology was transferred to commercial harvesters in two Maine communities: Wiscasset (1997 and 1998) and Perry (2000). Impounded clams ( x̄=21.8 kg/cage; n=18) lost, on average, 5 kg/cage in 1997 and 1998, whereas no significant net loss in wet weight occurred in cages deployed in 2000 ( x̄=23.2 kg/cage; n=3). Differing harvesting and handling methods of individual clammers, prior to impounding clams, likely explains the variation in weight lost during the impounding periods. The difference in price per live kilogram between the beginning of the impounding period and the August sale date resulted in an average gain of $13.60/cage for clammers in 1997 and 1998 and $57.73/cage in 2000. Simple culture techniques can be used to increase the value of the live harvest of soft-shell clams along the coast of Maine. Clam impoundments may be a way for communities that co-manage the public clam resource with the state's marine resource agency to generate funds to pay for traditional management schemes, as well as enhancement programs that employ hatchery-reared juveniles. In addition, an indirect benefit of clam impoundments might be to create spawner sanctuaries since animals are impounded during the time when gamete release occurs.

The influence of pore‐water chemistry and physiology on the distribution of vesicomyid clams at cold seeps in Monterey Bay: Implications for patterns of chemosynthetic community organization

Analyses of sulfide, methane, oxygen, and CO2 in pore‐water samples from three cold seep sites in Monterey Bay indicate that fluid chemistry is a strong determinant of the distribution of chemolithoautotrophic vesicomyid clams. The distribution of Calyptogena pacifica and Calyptogena kilmeri were aligned closely with sulfide concentrations at all cold seeps and reflected species‐specific capabilities for sulfide binding. Live clams occurred only in sediment where sulfide was detectable. Sulfide was not detected in the absence of vesicomyid clams. The relative abundances of five vesicomyid species varied greatly among seeps. C. kilmeri accounted for 85–99% of all vesicomyids at seeps with high sulfide content, and C. pacifica dominated (73%) seeps with low sulfide levels. These species were also partially segregated along sulfide gradients from the center to the margin of seeps, analogous to zonation of rocky intertidal communities. We hypothesize that the absence of thiotrophic or methanotrophic mytilid mussels from Monterey Bay cold seeps is related to the lack of physiological specializations for concentrating reduced sulfur compounds or methane and the absence of hypersaline brines that could extend the persistence of methane or sulfide‐rich fluids very near the sea floor.

Respiration Rates of Live Clams (Mercenaria mercenaria; Hard Clams) in Modified Atmospheres at Various Temperatures

ABSTRACT Respiration rates of live clams were measured as a function of O2 and CO2 at 5, 15 and 25°C using the closed system method. The respiration rates were found to increase with increasing CO2 and decreasing 02-this respiratory behavior was opposite to that of fresh produce. The respiration rates followed the Arrhenius relationship, with activation energies ranging from 35.6 to 41.0 kj/ mole, which were little affected by O2 and CO2 and were lower than those of some fruits. The respiratory quotients were between 1.4 to 1.9. Some practical implications of the findings on modified atmosphere storage and packaging of live clams as well as further research needs are discussed.

Effect of Storage Temperature on Stress Levels in Live Clams (Paphies donacina; tuatua)

Live New Zealand subtidal clams (Paphies donacina; tuatua) were stored in polyethylene-lined polystyrene boxes in an air chiller at 4oC and 0oC. Stress levels were monitored by measuring the accumulation of two glycolytic metabolites, D-lactate and octopine, and by measuring changes in adenylate energy charge (AEC). Tuatua mortalities were higher during storage at 0°C. Storage temperature affected the rate of D-lactate production and the ability to maintain AEC. D-lactate and/or AEC levels are useful indices of live quality during post harvest handling when product is stored out of sea water.

Surficial evidence of fluid expulsion from the Costa Rica Accretionary Prism

The nature and distribution of authigenic carbonates, chemosynthetic bacterial mats, and unique macrobenthic chemosynthetic communities of bivalves and tube worms are important for evaluating and reconstructing present and past fluid venting of accretionary complexes. This paper describes the authigenic carbonates, chemosynthetic fauna, and fluid venting observed at the four tectonic regions of the Costa Rica accretionary wedge in February 1994 during an ALVIN diving program of 20 submersible dives. We found no surficial evidence of highly focused fluid venting at the toe of the prism (outermost 3 km), as implied by the absence of authigenic carbonates and chemosynthetic fauna. The absence of vent communities on the lower 3 km of the prism and the relatively elevated heat flow with respect to the adjacent, incoming Cocos plate (Langseth and Silver, this issue), suggests diffuse, rather than focused flow through the toe of the prism. Twelve active and relict vent sites marked by small clusters of live vesicomyid clams are localized at the bases and tops of out‐of‐sequence‐thrusts, implicating fracture permeability as the fluid conduit in the lower slope region (but upslope from the toe). Vast authigenic carbonates and seven active and relict vent sites marked by large, dense clusters of chemosynthetic organisms predominate the largest mud diapir in the mid‐slope region. Fluid expulsion appears to be more restricted on the upper slope, with only 2 small but dense vents marked by chemosynthetic fauna observed at one wall of one canyon.

Predation intensity in estuarine soft bottoms: between-habitat comparisons and experimental artifacts

The aim of this study was to determine whether experimental artifacts have the potential to bias comparisons of relative predation intensity among different soft-sediment estuarine habitats. A field experiment was used to test (1) whether predation intensity on the infaunal clam Mercenana mer- cenarja (L ) differed between shallow-subtldal and intertidal sand flats, (2) whether predation on clams differed between intertidal sand flats and vegetated habitats (the e d g e of Spartina alternjflora (Loisel) salt marshes) of similar elevation, a n d (3) whether the outcome of these comparisons was influenced by the experimental method used. For mobile prey, some restraint on prey movement is typically required to compare predation intensity among different habitats. This is most often achieved by tethering prey. Tethering and other experimental interventions may induce different experimental artifacts In esti- mates of p r e d a t ~ o n intensity In d~fferent habitats, which would invalidate between-habitat comparisons (Peterson & Black 1994: Mar Ecol Prog Ser 111:289-297). 1 used colnblnations of 2 types of prey restraint, tethers and buried fences, to test for possible interactive effects of habitat and prey restraint on prey mortality. Tethered or untethered clams were deployed within fenced or unfenced field plots within each habitat type, in a factorial design, and were exposed to the natural assemblage of predators for 1 wk. W i t h ~ n each habitat type, both tethering and fencing increased the proportion of clams recov- ered live after I wk compared to the treatment in which no prey restraints were used. Slynificantly more live clams were recovered in the intertidal sand flats than In the subtidal sand bottoms wlthin field plots enclosed with buried fences, suggesting lower predation intensity in the Intertidal than in suhtidal sand flats. In contrast, there was no significant difference in proportions of live clams between subtidal sand bottoms and intertidal sand flats within unfenced plots. These results were obtained with both tethered and untethered clams Significantly more clams were recovered live in intertidal sand flats than in intertidal salt marshes of similar elevation in all treatment combinations, suggesting lower predation intensity in unvegetated than in vegetated habltats Thls result was unexpected because habitat structural con~plexity is known to decrease predation rates in other shallow marlne habitats, such as rocky intertidal habitats and seagrass beds. Results of this field experiment indicate that prey restraints can bias not only estimates of predation intensity within a single habitat type but can also bias between-habitat comparisons of predation intensity, probably by causing experimental artifacts of dif- ferent magnitudes in each habltat. The actual magnitude of experimental artifacts in each habitat type can only be estimated with direct observations of predator-prey Interactions in the field.

Behavioral Control of Swash-Riding in the Clam Donax variabilis.

Clams of the species Donax variabilis migrate shoreward during rising tides and seaward during falling tides. These clams spend most of the time in the sand, emerging several times per tidal cycle to ride waves. Migration is not merely a passive result of waves eroding clams out of the sand; rather clams actively jump out of the sand and ride specific waves. Such active migration is experimentally demonstrated during a falling tide by comparing the motion of dead and live clams; live clams emerge from the sand and move seaward even when dead ones do not. As low tide approaches, live clams become progressively less active. They cease migrating for 2 hours around low tide and resume jumping to migrate shoreward after the tide has turned. During the rising tide, far from being passive, the clams jump out to ride only the largest 20% of waves. Specifically, they choose swash that have the largest excursion, i.e., those swash that move furthest on the beach.

Strategies of anaerobiosis in New Zealand infaunal bivalves: Adaptations to environmental and functional hypoxia

Abstract Under hypoxic environmental conditions, slowly burrowing bivalves such as the pipi (Paphies australis) and cockle (Austrovenus stutchburyi) support anaerobic energy production through the pyruvate reductase enzymes strombine dehydro‐genase and alanopine dehydrogenase. Rapidly digging surf clams such as the tuatua (P. sub‐triangulatum) and trough shell (Mactra discors) do not fare as well at low oxygen levels, but perform better under the functional anaerobiosis generated by burrowing, and energy production is supported by octopine dehydrogenase. Muscle buffering capacity is higher in rapidly burrowing species and is correlated with total pyruvate reductase activity. Anaerobic pathways in P. subtriangulatum led to both D‐lactate and octopine accumulation during environmental hypoxia, but only octopine accumulated during burrowing. Bivalves adapted to environmental hypoxia maintained high adenylate energy charge (AEC) under anaerobiosis, indicating a close matching of ATP production to consumption. AEC fell in P. subtriangulatum during environmental hypoxia. The significance of these findings is discussed within an ecological context, and in relation to the storage of live clams for the seafood industry.

Behavioural Plasticity in Prey-Size Selectivity of the Blue Crab Callinectes sapidus Feeding on Bivalve Prey

Prey-size selectivity of predators can play an important role in determining the predators' impact on their prey. In marine systems, a pattern of preference for small-sized molluscan prey is widespread among crustacean predators, even though predators are often able to consume prey over a wider size range. In laboratory tests the blue crab Callinectes sapidus showed preference for smaller individuals of the hard clam Mercenaria mercenaria. This was true for crabs starved for different durations of time, prior to experiment. Hungrier crabs tended to be less selective than the less hungry ones, although not significantly so. In order to determine whether such selectivity is hard-wired (i.e. engrained) or can be modified through experience, adult blue crabs were tested for preference between two different sizes of hard clams after a phase of conditioning on different combinations of live and sham (i.e. empty valves glued together and deployed in living position) clams of the two sizes. In the conditioning trial, crabs consumed more sham clams of both sizes than live clams, although sham clams did not yield any energy return. The greater consumption of sham clams by blue crabs might be explained by the lower cost of crushing dead clam shells, as dead shells seemed to be more brittle than the live ones. Conditioning significantly affected size selectivity in the subsequent test trial. Crabs assigned to different conditioning treatments consumed significantly different proportions of large clams in the test trial. In particular, crabs that had consumed greater proportions of large (sham) clams during the conditioning trial also ate significantly greater proportions of large (live) clams in the test trial than those which had consumed greater proportions of small (sham) clams during conditioning. These results indicate that the blue crabs' preference for small-sized clams does not result from a fixed decision rule and suggest that crabs might modify their preferences through experience. Furthermore, the relative strength of shells seemed more important than profitability ratios in determining patterns of prey-size consumption. An understanding of what perceptual and cognitive constraints underlie feeding preferences of'keystone' marine predators could help in making predictions about the impact of such predators on prey communities.

Odor plumes and how blue crabs use them in finding prey.

Orientation of animals using chemical cues often takes place in flows, where the stimulus properties of odorants are affected by the characteristics of fluid motion. Kinematic analysis of movement patterns by animals responding to odor plumes has been used to provide insight into the behavioral and physiological aspects of olfactory-mediated orientation, particularly in terrestrial insects. We have used this approach in analyzing predatory searching by blue crabs in response to plumes of attractant metabolites released from the siphons of live clams in controlled hydrodynamic environments. Crabs proceed directly upstream towards clams in smooth-turbulent flows and show high locomotory velocities and few periods of motionlessness. Crabs assume more indirect trajectories and display slower locomotion and more stopping in rough-turbulent flows. This degradation of foraging performance is most pronounced as flow shifts from a smooth- to a rough-turbulent regime, where the change in hydraulic properties is associated with contraction of the viscous sublayer region of the boundary layer. Because flow in this region is quasilaminar, the viscous sublayer may be a particularly effective vehicle for chemical stimulus transmission, such that orientation is severely compromised when it is reduced or removed. Our results also suggest that rheotactic and chemical information are both necessary for successful orientation. Perception of chemical cues acts to bias locomotion upcurrent, and feedback from odorant stimulus distributions appears directly to regulate subsequent stopping and turning en route to prey. Although the mechanisms of orientation to odorant plumes displayed by insects and blue crabs are largely similar, blue crabs appear to rely more heavily on spatial and/or temporal aspects of chemical stimulus distributions than has been suggested for insect systems.

Sulfide and Carbon Dioxide Uptake by the Hydrothermal Vent Clam,Calyptogena magnifica,and Its Chemoautotrophic Symbionts

The ability of intact hydrothermal vent clams, Calyptogena magnifica, to take up sulfide was tested in pressurized aquaria. In addition, stimulation of carbon fixation by sulfur substrates was tested in vitro with gill-symbiontpreparationsfrom live clams. The clams had the ability to concentrate sulfide from the medium, using the high-afinity sulfide-binding component in their serum, by about one order of magnitude, reaching internal sulfide concentrations as high as 6.6 mM. This binding ability was shown to be reversible in vivo. These clams were also shown to accumulate thiosulfate in their blood to about 1 mM and to quickly lose it when sulfide was removed The symbionts were shown to use sulfide as a substrate for carbon fixation, and the data also suggest that they can use thiosulfate. The symbionts were shown to be quite sensitive to sulfide, with inhibition of carbon fixation occurring at low sulfide concentrations. Incubation media containing sulfide-binding substances, either Riftia pachyptila hem...

A geological cross-section of the Vema fracture zone transverse ridge, Atlantic ocean

This paper presents a detailed geological account of five Nautile dives along the north flank of the Vema fracture zone's transverse ridge near 42°42′W. It shows the existence of three EW trending geological domains: (i) the lower slopes of the transverse ridge's flank, with outcrops of serpentinized mantle peridotites and amphibolites, and talus covered intervals which yielded blocks of amphibolite facies metadolerites and gabbros. EW-trending alignments of live clams in this lower domain are interpreted as marking the trace of active faults; (ii) an intermediate domain of more moderate slopes, heavily covered with pelagic ooze, with rare outcrops of gabbro and of consolidated limestones; (iii) an upper domain of steeper slopes, which extends up to the transverse ridge's crest and exposes a sheeted dike complex and its transition to the uppermost crustal unit of lava flows, pillow lavas and basalt breccia. The dike margins are vertical, and parallel with the Mid-Atlantic Ridge. There is no indication for recent tectonic activity in the intermediate and upper domains. We propose that the apparent crustal thickness below the north wall of the transverse ridge, defined by seismic and gravity studies, may be a direct function of the extent of tectonic slicing and serpentinization of the upper mantle and lower crustal rocks which outcrop along this wall.

Testing a Paleoecology Matrix Model: Estimates for a Sphaerium Population in Equilibrium with Its Death Assemblage

A paleoecologist may wish to estimate the age—specific mortality rates and fecundity rates of the population that generated the death assemblage under study. We report the result of an analysis for this purpose applied to a living bivalve mollusk population which can be assumed to be in equilibrium with its death assemblage. A Leslie matrix model that includes age—specific rates of generation, and of decay, of the death assemblage is applied to grab—sample data from a Sphaerium striatinum population in an artificial hard—water lake, Minnedosa Lake, Manitoba, Canada. The samples yielded both live clams and empty shells. Shell length was used as a measure of relative age. Mortality rate in the living population were estimated from the death assemblage, and then compared with direct estimates of the mortality rates for the living population. Close agreement was obtained, providing some validation of this approach to estimation of life history parameters of ancient populations.

Types of Clostridium perfringens Isolated from Selected Foods

To determine the proportion of type A Clostridium perfringens occurring among C. perfringens isolates obtained from foods, strains were typed by the mouse serum neutralization method. Of 339 isolates from ground beef, ground pork, ground turkey, live crab, cured sausage, and live clams. 320 (94%) were type A. The remaining 19 isolates produced insufficient exotoxin for typing. The predominance of type A strains from the foods surveyed indicates that definitive typing of strains isolated from these foods, when suspected of causing foodborne disease, is not warranted.

Deposition of Clastic Sediments by Clams

ABSTRACT The role of clams and other filter feeders in sedimentation probably far exceeds the generally recognized accumulation of their skeletal remnants. In the course of their feeding, these organisms constantly remove suspended inorganic and organic particles from water, combine them with organic binder, and deposit them as excreta. The sticky excreta (and shells) trap sand and other particles and contribute to sedimentation. The amount of clastic sediments deposited in this manner is significant, for example, in the 113-mile-long Delta-Mendota Canal in the western San Joaquin Valley, California. The sediments consist of 20-35 percent fines which were probably precipitated as excreta, 35-50 percent sand, and 30 percent clamshells. Highly eutrophic, turbid deltaic water which is pumped into the canal supports an abundant, varied biota. Asiatic clams (Corbicula fluminea) are particularly numerous. The average number of live clams per square foot of sediments is in the order of 1000. Laboratory pumping rate of a one-year-old Corbicula appears to be about 20 cc/hour. There is a general decline of clam infestation in the downstream direction, away from the Delta: In 1965-66, biomasses of Corbicula declined from about 140 (pool 1) to 2.5 (pool 18) tons per linear mile. Average sedimentation rates decline from about 292 yd3/mi/yr in pools 1 through 5, to 9 yd3/mi/yr in pools 15 through 19. Apparently smaller pumping-deposition of suspended particles by clams in downstream reaches results in correspondingly lower sedimentation rates.

The Feeding Behavior of the Seastar Evasterias troschelii Stimpson

Kymograph recordings of shell movements of 4.0–5.5 cm long clams (Protothaca staminea) during attacks by the seastar (Evasterias troschelii) showed: (1) in 21 experiments the valves were pulled apart at a mean rate of about 1.0 mm per minute, as measured at the mid‐ventral edge of the clams; (2) clams constantly tried to close during the initial opening of them by the seastars and then at longer intervals thereafter for a period usually not exceeding 4 hours.A specially constructed, false lucite “clam” containing Mytilus meat as bait was opened by Evasterias against known resistances applied to the approximate center of the upper, free‐moving valve of the “clam.” Kymograph recordings of shell movements of this “clam” during seastar attacks showed: (1) the curves showing the openings agree closely with those showing openings of live clams; (2) an average sized Evasterias may exert forces in excess of 5000 grams; (3) having lifted such weights, the seastar may hold them lifted for several hours; (4) in 14 experiments, weights varying from 700 to 5500 grams were lifted at an average speed of about 0.8 mm per minute, equal to an increase in gape of about 1.2 mm per minute during the lift. Maximum lifts varied from 2.8 to 13.5 mm with a mean of 6.6 mm.Experiments and observations showed that only the longitudinal musculature of the tube feet is responsible for the forces exerted by the seastar in opening bivalves. However, there are strong indications that the seastar is capable of “locking” itself in a rigid state before commencing the pull.If prevented from applying force, Evasterias will still succeed in feeding on bivalves, but the digestion period is considerably prolonged due to difficulties in inserting all lobes of the stomach into the prey.