Edmonds Discovery Programs
A Leader in Conservation Education since 1980

Invasive marine life threatening Puget Sound and displacing native species.

In this ever more interconnected world the Puget Sound continues to face an onslaught of alien species being introduced from the waters of Asia, Europe and elsewhere. Once here these species may become established, or may even thrive - out competing native species within a given ecological niche.

Some of these invaders have been here long enough that few of us remember a time without them, but others are a new and potenially dire threat. Arriving as stowaways on cargo vessels, these new invasives may encrust a ship's hull, or swim in the vessel's ballast water.

During the 1920's when a number of species of clams were introduced purposefully and accidentally to our area, the environment didn't collapse, and to the untrained eye life in the intertidal zone appeared much as before. Closer inspecition found native species, like the Olympia Oyster pushed to near extinction, and native Littleneck clams numbers greatly reduced.

The discovery of invasive colonial tunicates, a type of sea-squirt, in the Edmonds Underwater Park in 2004 signaled a new wave of invaders. These tunicates cover the sea bottom, smothering all other life. Spreading extreamly fast, these colonies have wiped out much of the Grand Banks in the Atlantic Ocean in just a few years. The Edmonds colony was destroyed, but the species has spread to many other areas of Puget Sound and there is no going back.

Here is a survey of invasives found on our Edmonds beaches, both recent and historical.


Colonial Tunicate

Found Edmonds Underwater Park in 2004. Now spread to other locations in Puget Sound. A very serious threat to the ecosystem.


Solitary Tunicate/Sea-squirt

These recent invaders have been found on the breakwater at Olympic Beach and in the Marina.

Perna viridis

Asian Green Mussel

In 2006 a single specimen was found on Olympic Beach. A huge problem on the east coast, these bright green mussels may not become established due to our occasional freezes.

Purple varnish clam

Purple Varnish Clam

First found in Puget Sound in the late 1990's, this clam is thought to have arrived from Asia in Ballast water. They first appeared in Edmonds around 2006 and are still uncommon.

Gallo mussel

Mediterranean Mussel/Gallo Mussel

This European native used in aquaculture is found throughout Puget Sound and interbreeds with native blue Mussels.

Pacific Oyster

Pacific Oyster

Also known as the "Japanese Oyster." Introduced from Japan in the early 1900's, this exotic species became naturalized and is an important commercial crop.

Manila clam

Japanese Littleneck Clam

This clam was accidentally introduced into Puget Sound in the 1920's in shipments of Pacific Oyster seed stock. This species has out competed Native Littleneck in many places.

Soft shell clam

Soft-shell Clam

This species is believed to have been introduced from the Atlantic Ocean sometime around the 1920's.