Why Are There So Many Purple Varnish Clams in Alsea Bay?

The Accidental Arrival: How Purple Varnish Clams Got Here

Let's start with the origin story. Purple varnish clams didn't swim here on their own—they're not native to Oregon or anywhere in North America.

According to the Smithsonian Environmental Research Center, Nuttallia obscurata "is native to the Northwest Pacific from Russia, Japan and China. In 1991, it was discovered in Blaine, Washington, at the Washington-British Columbia border. It is thought to have been introduced as larvae in ballast water from vessels entering the nearby Port of Vancouver."

That's right—these clams hitched a ride across the Pacific Ocean in the ballast water of cargo ships. The University of Washington notes: "Nuttallia obscurata is believed to have arrived in the Strait of Georgia region (near Vancouver, British Columbia) in ballast water (a by-product of shipping)."

According to a Canadian Department of Fisheries and Oceans study, "The varnish clam has a wide coastal range with the southern limit reported as far south as Alsea Bay, Oregon."

By the time Alsea Bay became part of their range, purple varnish clams had already proven themselves to be remarkably successful colonizers throughout the Pacific Northwest.

What Makes Purple Varnish Clams So Successful?

So they arrived in ballast water—but that doesn't explain why they're now the dominant clam species in Alsea Bay. Many introduced species fail to establish themselves. What makes purple varnish clams different?

1. They're Ecological Generalists with Broad Tolerances

Research from Western Washington University found that "Nuttallia obscurata gill tissue had significantly greater tolerance to higher temperatures and to lower salinities than did the two other" clam species studied.

In other words, purple varnish clams can survive in conditions that would stress or kill other clam species. They tolerate:

• Wide temperature ranges (from cold to warm water)
• Variable salinity (from brackish to full seawater)
• Different substrate types (sand, mud, gravel)
• Various tidal zones (including high intertidal areas avoided by other clams)

2. They Reproduce Prolifically

Purple varnish clams are breeding machines. According to research from Vancouver Island University, these clams have "high reproductive potential" with:

• Extended spawning seasons compared to native species
• Large numbers of larvae produced per individual
• Rapid growth to reproductive maturity
• Multiple spawning events per year

This reproductive strategy means that once a small population establishes itself, it can explode in numbers within just a few years.

3. They Occupy an Underutilized Niche

Here's where it gets really interesting. A University of British Columbia study found: "This study suggests that the varnish clam invasion in the SoG [Strait of Georgia] was successful because this species was able to occupy the high intertidal zone, an area that native clams generally avoided."

Purple varnish clams can thrive in the high intertidal zone—the area that's exposed to air for longer periods during low tide. Most native clam species prefer lower intertidal areas that stay wet longer. By colonizing this less-competitive zone, purple varnish clams essentially found real estate that nobody else wanted.

4. Alsea Bay Provides Perfect Conditions

Now let's talk specifically about Alsea Bay. Why is this particular estuary so hospitable to purple varnish clams?

According to ODFW's 2015 Alsea Bay clam density study: "Many purple varnish clams as well as cockle and gaper clams are found in the sand flats of the lower bay."

Alsea Bay offers:

• Extensive mudflats with the sandy-mud mix they prefer
• Protected waters that reduce wave stress
• Good salinity gradients from river mixing
• Nutrient-rich waters for filter feeding
• Minimal competition in the higher intertidal zones

The ODFW Alsea Bay clamming guide specifically identifies a "Purple varnish clam bed, east of bridge" location, noting their abundance in this area.

Are Purple Varnish Clams Harmful to Native Species?

Here's the big question on everyone's mind: Are these invasive clams hurting our native bay clam populations?

The answer is... complicated. According to a review of varnish clam research: "Varnish clams bury deeper than co-occurring species, decreasing competitive effects on native species may simply not yet be detectable."

What the Research Shows

A study published in Marine Ecology Progress Series examined the "invasion dynamics of the varnish clam" and found that while they are established as "a significant threat to native biodiversity," the specific impacts vary by location.

So far in Alsea Bay:

• Native clams are still present in their traditional zones
• Gapers, cockles, and butter clams continue to thrive
• Purple varnish clams mostly occupy different depth zones
• Long-term impacts are still being studied by ODFW

Identifying Purple Varnish Clams

So how do you tell purple varnish clams from native species? It's actually pretty easy once you know what to look for.

Key Identification Features

According to ODFW: "The purple varnish clam is named for the purple hue found inside the clam and the shiny varnish over the brown color outside the shell."

The Washington Department of Fish & Wildlife provides this detailed description:

Shell characteristics:

• Oval shaped, thin and flat
• Up to 3½ inches long
• Thick, shiny periostracum (outer layer)
• Brown exterior that often peels like old varnish
• Purple coloration on the interior (this is the dead giveaway)
• Large external hinge
• Relatively flat profile compared to butter or littleneck clams

When digging:

• Found 3-14 inches deep (usually shallow)
• Leave small round holes in the substrate
• Often in dense clusters
• Siphons are long, thin, and translucent white
• Foot is large and can be fully retracted

Harvesting Purple Varnish Clams in Alsea Bay

Because purple varnish clams are so abundant and are considered an invasive species, Oregon has set generous harvest limits to encourage people to collect them.

Current Regulations

According to ODFW shellfish regulations:

How to Harvest Purple Varnish Clams

Good news: purple varnish clams are among the easiest clams to dig!

Tools needed:

• A simple garden shovel or rake
• Bucket or mesh bag
• Rubber boots
• Your shellfish license

Technique:

1. Look for small round holes in the mudflats during low tide
2. Dig 4-8 inches down (they're shallow compared to other clams)
3. Sift through the substrate—you'll often find multiple clams in one spot
4. Collect quickly—they burrow back down if you're slow
5. Your 72-clam limit will fill up fast!

Are Purple Varnish Clams Good to Eat?

Absolutely! In fact, that's another reason ODFW wants people harvesting them.

According to ODFW: "Purple varnish clams were introduced to Oregon, most likely from ballast waters from Asia. They can be a tasty addition to your pasta, chowder, or curries."

Flavor and Texture

The Sound Water Stewards describe them: "When the shell dries out this layer often flakes off. The inside of the shell is a beautiful purple color. Varnish clams are an introduced, often invasive species in the Salish Sea. To encourage clam diggers, it has more recently been called the savory clam."

Culinary characteristics:

• Sweet, mild flavor (less "clammy" than some native species)
• Tender texture when cooked properly
• Larger than Manila clams but smaller than gapers
• Versatile in recipes (steam, fry, chowder, pasta)
• Clean-tasting—they filter-feed in clean bay waters

Cleaning and Preparation

Purple varnish clams are relatively clean compared to other species:

1. Rinse off mud and debris
2. Let them purge in clean saltwater for 2-3 hours (they'll expel sand)
3. Scrub shells if desired
4. Cook as you would any clam—steaming is popular
5. Discard any clams that don't open during cooking

Best Spots for Purple Varnish Clams in Alsea Bay

The Future of Purple Varnish Clams in Alsea Bay

So what can we expect going forward? Here's what the science tells us:

They're here to stay. Purple varnish clams are now a permanent part of the Alsea Bay ecosystem. No feasible eradication method exists once an invasive bivalve establishes breeding populations.

Populations may stabilize. According to SERC, after initial rapid expansion, purple varnish clam populations tend to reach equilibrium with their environment. They're abundant but not necessarily still increasing exponentially.

Harvest helps management. The generous daily limits encourage recreational harvest, which helps control populations and reduces potential competitive pressure on native species.

Research continues. ODFW's SEACOR program continues monitoring Alsea Bay clam populations to track long-term changes and impacts.

Conclusion: Understanding Our Changing Bay

So why are there so many purple varnish clams in Alsea Bay? The answer involves:

• An accidental introduction through ballast water in 1991
• Remarkable physiological tolerance to varied conditions
• High reproductive capacity and rapid population growth
• Ability to thrive in ecological niches less used by native species
• Perfect habitat conditions in Alsea Bay's protected mudflats
• Lack of natural predators or parasites in their new range

Purple varnish clams represent a new reality for Oregon estuaries. They're not going away, but they also don't appear to be causing the catastrophic damage that some invasive species create. Instead, they've become an abundant, harvestable resource that ODFW actively encourages us to enjoy.

For those of us who love Alsea Bay—whether as longtime Waldport residents or visitors falling in love with the Oregon coast—purple varnish clams are now part of our story. Understanding where they came from, why they're so successful, and how to harvest them responsibly helps us adapt to our changing coastal ecosystem.

Next time you're out on the mudflats during low tide and your bucket fills with purple varnish clams in twenty minutes, you'll know exactly why. And when you're enjoying them steamed with butter that evening, you can appreciate that you're participating in the ongoing story of an Asian clam that found a new home in our bay—and thrived beyond anyone's expectations.

Happy clamming, Waldport!