Panopea generosa

From marinelife1011

The word geoduck comes from the Nisqually tribe of Washington State, the original hunters of Panopea generosa and the earliest settlers of southern Puget Sound. They called their giant catch gweduc, a name that the first Europeans in the Northwest changed to gooeyduck or goeduck, the two alternate spellings most often used today. Settling on a mutually acceptable scientific name for the geoduck has been equally difficult, with a total of 14 different combinations of genus and species in use during this and the previous century. ^[1]

Size: The largest burrowing clam int the world, attaining a shell length of at least 8.5 inches (21.6 cm) and a live weight (including the shell) of 7 pounds (3.2 kg). A few giants have been recorded at 14 and even 20 pounds (6.4 and 9 kg). In buried adults, the long contractile siphon may extend 39 inches (1 m) to reach the surface of the seabed.

Range: The West Coast of North America, from Alaska to Baja California.

Habitat: Lower intertidal and subtidal zones of bays, sloughs, and estuaries, to depths of around 360 feet (110 m); most abundant between 30 and 60 feet (9.1 and 18.3 m) below the mean low tide mark. Burrows in a variety of substrates, ranging from soft mud to pea gravel, mostly in stable mud or sand bottoms.

Food: Phytoplankton, primarily diatoms and dinoflagellate species.

Predators: Crabs, shrimp, sea stars, snails, fish, sea otters, and humans.

Life Span: Well over 100 years. ^[2]

Contents 1 Anatomy 2 Life Cycle 3 Scientific Tools as Bioarchives 4 Fishing Industry 5 References

Anatomy

External

A geoduck's shell is rectangular, up to 9 or 10 inches (23 to 25 cm) long and 5 inches (13 cm) in height. Both valves are equally proportioned and sculpted with concentric but irregularly shaped growth lines. A small but prominent ligament hinge holds the two valves together. The valve's grayish white outside surfaces are covered by the periostracum, a thin, light brown covering that shields the shell's middle layer of calcium carbonate crystals from scratches or abrasions. A geoduck's siphon is also known as its neck. This appendage could more accurately be described as a tail, since it originates from the posterior end of the clam. Within this siphon are two long tubes, the inhalant and exhalant channels. To escape predators, the geoduck can rapidly retract its neck, expelling a double-barreled blast of water through these tubes. Far less conspicuous is the foot, a protuberance that, because of its shape, has given bivalves yet another classificatory title, the Pelecypoda animals. Young geoducks and many other kinds of clams use the foot to burrow into sand and sediments, alternately extending and contracting the muscular appendage to pull the rest of the animal downward. ^[3]

Internal

Nearly all of the clam's organs are hidden beneath its fleshy mantle and enveloped by a large, cream colored glob of a gonad. As with all clams, male and female geoduck gonads are visually indistinguishable, requiring a microscope to tell the two sexes apart. Lining both inhalant and exhalant siphons are millions of specialized cells. Each of these cells is equipped with a lashlike filament called a lateral cilium. By waving these filaments in unison, the cells generate water currents, which flow down the inhalant siphon and bathe the clam's innards. A pair of gill sheets retrieve oxygen from the slow moving water and transfer it to the bloodstream. Geoduck gills also play a part in feeding. As water moves through the clam's guts, any phytoplankton, zooplankton, or other floating tidbits become trapped by the coating of mucus on each gill sheet. ^[4]

Life Cycle

Reproduction

Because geoducks are broadcast spawners, they don't need to recognize members of the opposite sex. Eggs and sperm are released several times in one spawning season, typically from late winter to early summer, with the greatest activity during May and June. Triggered by rising water temperatures and other cues from the environment, mature males release millions of free-swimming sperm. The presence of the sperm in the water stimulates mature females to begin spawning, releasing as many as 5 million eggs at a time. Females release as many as 10 batches of eggs each season. ^[5]

Metamorphosis

Like all other mollusks, geoducks undergo a complex metamorphosis, dramatically taking new shapes several times in their first weeks of life. The first stage is the trochophore, a ciliated larva barely visible to the naked eye. The trochophore's body then begins to change, acquiring an excessory organ called a velum, which is a parachute-like appendage used for swimming. After the tiny larva's shell begins to elaborate, it enters the prodissoconch stage. When the geoduck loses its velum and swimming abilities, it sprouts a set of spines on the outer edges of its shell. It drops from the upper water column, and, settling on the seafloor, begins to act more like a grown-up clam. This is called the dissoconch stage. By the end of the second year, as they reach adult size and a maximum depth of 3 feet (91 cm), they have become progressively more sedentary in nature. ^[6]

Scientific Tools as Bioarchives

Because of their large size and abundance, geoducks are used as scientific tools and as subjects for shell fisheries with highly commercial value. They are thus one of the most highly used marine bivalves in British Columbia and Washington state for population and growth analysis, both as organisms whose living representatives provide ecological data and as mineralized shells that are incremental records of changes in recent Pacific Northeast climate. Another important perspective is the long stratigraphical range of the genus Panopea from Cretaceous to Recent. As the adults of P. abrupta and other Panopea species typically live deeply buried within the sea bottom, the preservation potential of their shells is likely to be high. The spacio-temporal range makes this genus suitable for studies on sclerochronology combined with biogeochemistry. Sclerochronology is about the temporal context of accretionary shell and skeletal materials. ^[7]

Fishing Industry

The world's first geoduck fishery was created in 1970, but demand was low due to its texture. Today, they sell in Asia for up to $30/lb. ^[8]

Its large, meaty siphon is now prized for its savory flavor and crunchy texture. Geoduck is also regarded by some as an aphrodisiac due to its phallic shape. The geoduck's high market value has created an $80 million U.S. industry, with harvesting occurring in both Washington state and the province of British Columbia. ^[9] It is one of the most closely regulated fisheries in both countries; in Washington, Department of Natural Resources staff are on the water continually monitoring harvests in order to ensure revenues are received. ^[10]

Aquaculture Industry and Ecological Consequences

The demand for Geoduck overseas has created a high demand for production in Puget Sound and British Columbia, an $80 million industry that is planning for major expansion. Geoducks are typically found in deeper waters than other shellfish- depths of 360 feet. This results in the planting of geoducks in PVC pipes along the lower intertidal on commercial property which, apart from appearing unsitely, become dislodged and are scattered along the shore line during storms. During the process of geoduck harvesting, aquaculturists must liquefy the surrounding substrate with water from a high-volume hose, disrupting the centuries-old layering of sediments. This disturbance of sediment can be harmful to the delicate and complex web of life that abounds in the top few feet and that sustains species far beyond the intertidal zone, such as fish and shorebirds. ^[11]

References

Gordon, David G. People for Puget Sound: Field Guide to the Geoduck. Seattle: Sasquatch Books, 1996. 12-43. Print.

Washington State Department of Fish and Wildlife. N.p., 2011. Web. 21 Feb. 2011. <http://wdfw.wa.gov/>.

www.wsg.washington.edu/research/geoduck/research/friedman_overview.

Shellfish Aquaculture Regulatory Committee, Washington State Department of Ecology, http://www.ecy.wa.gov/programs/sea/shellfishcommittee/index.

Goodwin, Lynn, and Bruce Pease. "Pacific Geoduck Clam." U.S Fish and Wilflife Service Biological Report 11.120 Dec. (1989). Web. 21 Feb. 2011.

Kozlof, Eugene. Seashore Life of the Northern Pacific Coast. (Seattle: University of Washington Press, 1983).

http://www.nbii.gov.