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What Lies Beneath

Liz Clift

This is part of a series on bivalves. Follow these links to read Parts 1 & 2 on oysters: an ultra-brief history on why we eat them and their role in an ecosystem.

There’s a marine clam so large that it can’t stuff itself in its shell. You might imagine that leaves it vulnerable to predators because its tender parts are so readily exposed (tender parts that are, apparently, lightly sweet and crispy).

But that clam also buries itself.

It’s the Pacific geoduck (pronounced gooey duck; Panopea generosa) clam, which has been reported to live more than 125 years. Like other bivalves, the geoduck filter feeds—which means it likely has some impact on water quality, although there don’t appear to be published studies on how much water an adult geoduck can filter a day or the degree to which it cleans the water relative to other bivalves.

Geoducks, like other bivalves spend the first weeks of their life in a larval state, floating around on ocean currents. When they begin to settle onto the substrate, they start to bury themselves, as deep as their siphons will allow. As they grow, they can bury themselves deeper, which provides additional protection from animals—including people—that might enjoy a tasty geoduck snack. Additionally, the pressure from the sand helps them keep their bivalve closed (the muscles which do this in other bivalves, like oysters, are not strong enough in geoducks to do this naturally). If you see one on the beach, in the wild, most likely you’ll notice it because it spurts a little fountain of water out occasionally, from its siphon. If you’re diving, you might only see the siphon, which resembles certain types of sea sponge (such as Alpysina archeri).

geoduck-in-hands-usda

Geoducks being held closed with rubber bands (Photo from USDA)

 

Like oysters, and many other mollusks, geoducks are a facet of the aquaculture/mariculture industry. Geoduck farms may look like a bunch of pipes plunged into a beach, which at low tide, may be exposed. Each pipe is seeded with a couple juvenile geoducks, which will remain in those pipes for a few years until they reach maturity (the exact timing of this depends on a number of factors, including water temperature). At that point, the geoducks are harvested by essentially super-saturating the surrounding sand with water and then extracting the geoduck by reaching one’s arm down into the pipe. The goal is to grab geoducks by their shell (so as not to damage the siphon) and then quickly wrap a rubber band around them to keep their shell closed.

There have been some concerns, however, from environmentalists and property owners about the impacts of these geoduck farms on coastal ecology. One study showed no net negative ecological impacts of geoduck (although there has been a shift of species in areas with geoduck farms—for instance, halibut and flounder, which prefer uninterrupted bottom areas are scarcer, but other animals that like to congregate (and hide) around structures have increased in population). In fact, there’s evidence that geoduck farming may even work to recruit* eelgrass, an endangered species. However, another study, completed in 2015, showed that the particular practices of farming geoducks may have a negative impact on species, such as birds, since the netting used to protect geoducks also serves to protect the prey those birds might otherwise forage, such as small crabs.

Geoduck Farm (Wikimedia Commons)

Geoduck Farm (Photo from Wikimedia Commons)

Like many things, it seems to be, in part, a matter of scale.  Double or triple the amount of geoducks  farmed in the Puget Sound area, and we might see more impacts from geoducks themselves. As of right now, the primary impacts seem to be the methods of farming, and perhaps changes to these methods, in a move to become more sustainable for impacted species (predator species, such as salmon, great blue heron, and others), is to come. After all, one of the largest shellfish farms in the region claims to have a vested interest in maintaining geoduck health as a means of sustaining their business.

 

*Unfortunately, if netting is used to cover the geoducks, to prevent easy predation, the removal and replacement of the netting can cause eelgrass to die back.

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