Panopea generosa

Geographic Range

Pacific geoduck clams ( Panopea generosa ) are native to temperate waters of the Pacific Ocean and subtropical areas of the Mexican Pacific. Populations of Pacific geoduck clams are concentrated off the west coast of North America, especially in Puget Sound. However, the geographic distribution of Pacific geoduck clams extends north to Alaska and south to Punta Canoas, on the peninsula of Baja California. As commercial fisheries attempt to expand geoduck aquaculture, individuals have recently been reported as far south as Guerrero Negro in Baja California Sur.

• Biogeographic Regions
• pacific ocean pacific ocean
  • native native

Habitat

Pacific geoduck clams are infaunal, meaning they live the substrate of relatively shallow (5 to 25 m deep) subtidal waters. The common name "geoduck" comes from the Salish word "to dig deep". Larval Pacific geoduck clams are planktonic, but juveniles and adults are infaunal, living in various substrates that can contain mud, sand, and gravel. Pacific geoduck clams can tolerate a wide range of salinity and temperature, especially as adults, but they are most commonly found in temperate marine environments.

• Habitat Regions
• temperate temperate
• saltwater or marine saltwater or marine

• Aquatic Biomes
• coastal coastal

Physical Description

Pacific geoduck clams are one of the largest known clams in the world, with an average shell length of 135 to 140 mm, but individuals are reported to reach shell lengths of over 200 mm. Their shells are generally quadrate (square-shaped) and have a thin, light brown outer layer, called the periostracum. In addition to their large shells, Pacific geoduck clams have a siphon that may extend over 1 m to reach out of substrate to the surface of the seabed. Pacific geoduck clams are reported to reach masses of over 3 kg in total. Juveniles have a large foot relative to their body size, which they use to dig into substrate on the seafloor. As Pacific geoduck clams mature, their foot gradually becomes proportionally smaller as they grow to adult size and lose the ability to dig. There are no significant differences in size between male and female Pacific geoduck clams, and sex can only be determined by microscopy of the gonads. Males usually achieve sexual maturity at a younger age and a smaller size. Environmental conditions, such as chemical concentrations, substrate composition, and water temperature, can affect the size, color, and shape of Pacific geoduck clam shells.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

Pacific geoduck clams go through seven distinct life stages common to most bivalve species. They are as follows: egg, trochophore larva, prodissoconch/veliger larva I, prodissoconch/veliger larva II, dissoconch/post-larval, juvenile, and adult. After spawning and fertilization, fertilized eggs undergo rapid cell division and develop into trochophore larvae, which are shaped like tops. Larval Pacific geoduck clams are motile and planktonic, whereas post-larval, juvenile, and adult Pacific geoduck clams are sessile and infaunal. Trochophore larvae have short cilia for swimming, as Pacific geoduck clams are planktonic in their larval stages. Within two days of hatching, larvae develop a straight-hinged shell and a velum, which is a ciliated organ used for swimming. This developmental stage is known as prodissoconch (veliger) I, or the straight-hinged larval stage. As they reach the prodissoconch (veliger) II stage, larvae develop rounded elevations, called umbones, on their shell hinges. Around 16 days after hatching, Pacific geoduck clam larvae lose their velum and therefore their swimming ability. They begin to develop spines along the edges of their shells and a muscular foot, which they use to crawl and dig. At this point in development, Pacific geoduck clams are considered to be in their dissoconch or post-larval stage. At this stage, they transition from a motile, planktonic lifestyle to a sessile, infaunal lifestyle. Dissoconch Pacific geoduck clams attach themselves to substrate using byssal threads and insert their foot into the substrate to dig. Once they reach their juvenile stage, which resembles the adult state, Pacific geoduck clams develop a siphon and can burrow more deeply into the substrate. When they are approximately 3 years of age and measure around 75 mm in shell length, Pacific geoduck clams are considered sexually mature adults. They grow rapidly until they are around 10 years old, after which their growth rate slows significantly. However, they exhibit indeterminate growth and continue to grow slowly throughout their life. As mature adults, Pacific geoduck clams lose the ability to dig and are completely sedentary.

• Development - Life Cycle
• metamorphosis metamorphosis
• indeterminate growth indeterminate growth

Reproduction

Pacific geoduck clams are dioecious and reproduce sexually. Reproduction occurs via broadcast spawning, wherein both sexes release their gametes into the water column and fertilization occurs externally.

Pacific geoduck clam adults are sedentary and are incapable of digging with their foot. Therefore, once buried in substrate, they remain there throughout their life. Adults reproduce sexually by spawning in a simple annual reproductive cycle. Males and females produce their gametes in September and spawning occurs from March to July. Spawning is usually triggered by increasing water temperature, though other cues, such as changes in water chemistry, can also affect the timing of spawning. Male Pacific geoduck clams typically begin the spawning process by releasing sperm, which in turn prompts females and other males to release their gametes. Females may produce up to one billion eggs, but only release a few million during each spawning event.

• Key Reproductive Features
• iteroparous iteroparous
• gonochoric/gonochoristic/dioecious (sexes separate)
• broadcast (group) spawning

Pacific geoduck clams exhibit no parental investment beyond the act of mating. They reproduce via broadcast spawning, so fertilized eggs are typically carried far away from their parents by ocean currents.

• Parental Investment
• no parental involvement

Lifespan/Longevity

Pacific geoduck clams are among the longest-lived animals known. Populations are usually comprised of adults ranging from 3 to 96 years of age, but there are many examples of individuals living past 100 years, with a maximum recorded wild lifespan of 146 years. Pacific geoduck clams exhibit high rates of mortality during early stages of development, including their planktonic and early settlement stages. However, once adults are submerged in sediment, mortality rates significantly. Pacific geoduck clams are less susceptible to predation if they are buried deeper into substrate they are found. Individuals buried at least 60 cm beneath the surface of the seabed cannot be reached by natural predators.

Behavior

Pacific geoduck clams are burrowing clams and individuals have been found buried up to 3 feet deep in the substrate of intertidal and subtidal zones along the northwestern coast of the United States. Due to their sedentary lifestyles as adults, individuals spend the majority of their development moving to and burrowing in an appropriate place in mud or sand. Pacific geoduck clams larvae are motile and can move relatively easily throughout the water column. However, the post-larval dissoconch Pacific geoduck clams develop a ciliated foot that allows them to crawl along the seafloor and begin burrowing into substrate. Post-larval dissoconch Pacific geoduck clams also release byssal threads from their foot, which allow them to anchor themselves to substrate. Juveniles begin burrowing into substrate using their foot until only their siphon is left exposed above the surface. As they develop and their siphon grows longer, individuals burrow deeper into the sand, up to a depth of 3 feet. As they develop into adults, their bodies grow and their foot becomes proportionally small, thus limiting the ability of adults to dig deeper into substrate. Adults are sedentary and move rarely, if at all.

• Key Behaviors
• motile motile
• sedentary sedentary

Home Range

There is limited information regarding home range of motile stages of Pacific geoduck clams. Juvenile and adult stages are primarily sedentary, and so do not have a meaningful home range.

Communication and Perception

Although there is limited information regarding sensory perception and communication of Pacific geoduck clams specifically, there is research on perception in closely related bivalve mollusks. In these species, sensory organs on the inhalant siphon detect changes in water chemistry and temperature, which are indicators of seasonal changes associated with breeding behavior.

• Perception Channels
• chemical chemical

Food Habits

Pacific geoduck clams are filter feeders, consuming microbes and other particles that they sift from the water column. They have ciliated ctenidia, or gills, that transport food particles to their labial palps, after which food passes through their digestive system.

• Other Foods
• microbes

• Foraging Behavior
• filter-feeding filter-feeding

Predation

Pacific geoduck clams in larval, post-larval, and juvenile stages are especially vulnerable to predation, as their siphons are not fully developed and they cannot burrow as deeply as older juveniles and adults. Small epibenthic predators such as sunflower seastars ( Pycnopodia helianthoides ), lean western nassa ( Nassarius mendicus ), and dock shrimp ( Pandalus danae ), have been documented preying on juvenile Pacific geoduck clams. Furthermore, red rock crabs ( Cancer productus ), slender crabs ( Cancer gracilis ), and epibenthic fish such as flatfishes (order Pleuronectiformes ) prey on juveniles and the siphons of adults through a process known as siphon cropping. Many of these predators also prey on juveniles that are buried just below the surface.

Ecosystem Roles

Pacific geoduck clams comprise a large portion of the infaunal biomass in their habitats. They can filter 7 to 20 liters of water per hour, which impacts the levels of phytoplankton and compounds in the water column. Pacific geoduck clams also produce waste, which they release into the water column, making them an important biodepositor. Nitrogen found in the waste of Pacific geoduck clams has been shown to benefit nearby aquatic plant communities. Pacific geoduck clams also serve as a prey source for fish, crabs, and other marine invertebrates.

Economic Importance for Humans: Positive

Pacific geoduck clams are a popular source of seafood. The shellfish industry in the Pacific Northwest is worth approximately $113 million per year. The Suquamish tribe in Washington state are major landholders of geoduck harvesting areas, and bring in around $6 million per year from the shellfish industry. Most of the harvested product goes to Asian markets in China and Japan, selling for as much as $50 per pound. The cultivation, harvesting, and packaging of Pacific geoduck clams and other shellfish has created thousands of jobs in the United States.

Pacific geoduck clams are also serve important roles in maintaining healthy coastal marine ecosystems, which in turn benefits coastal human communities.

• Positive Impacts
• food food

Economic Importance for Humans: Negative

Pacific geoduck clams have no known negative impacts on humans or the economy.

Conservation Status

Pacific geoduck clams are not evaluated on the IUCN Red List, and have no special status on any other national or international conservation lists. High demand for geoduck clams in Asia has caused the United States government to limit harvesting, which has increased the price per pound for Pacific geoduck clams. Because they have become valuable in Asian markets, poaching is becoming increasingly common. However, there are currently no conservation measures in place to protect Pacific geoduck clams specifically.

Other Comments

Wild and cultivated geoducks are harvested and eaten by humans. The artificial impact that human predation and cultivation have on the native wild biodiversity and adaptations has not yet been studied.

Additional Links

Encyclopedia of Life

Contributors

Alanna Cohen (author), The College of New Jersey, Bradford Newton (author), The College of New Jersey, Keith Pecor (editor), The College of New Jersey, Galen Burrell (editor), Special Projects.

References

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