The Alien Invasion of Humboldt Bay

October 1, 2002


In 1995, scientists discovered the European green crab had reached Humboldt Bay. This voracious predator decimated the soft-shell clam industry in Maine and Canada when it was accidentally introduced during the 1950's, and was first recorded on the West Coast in 1989. The green crab has since spread at a rate of more than 100 miles each year, making it the fastest expanding marine species ever.

The introduction of invasive species like the green crab is the second greatest threat to biological diversity after habitat destruction, and is costing millions of dollars each year in the U.S. Invasive species first arrived in Humboldt Bay when maritime trading began in the mid-1880's, but as a recent study shows, the pace of introductions in Humboldt Bay is now increasing dramatically.

A team of Humboldt State University professors and students recently undertook the most comprehensive survey ever completed of the algae, invertebrates, and fish in Humboldt Bay. This survey found that there are at least 65 invasive species in its waters today, including 60 species of marine or estuarine invertebrates, 2 species of marine algae, and one fish species. The team found 32 additional species that may have also been introduced into the Bay, but there is not enough information on these to be certain.

Ships are the primary transporters of invasive species in coastal waters, carrying plants and animals in ballast water and on the boats themselves. Hundreds of species arrive in U.S. waters from overseas each day, and while many cannot survive in their new environment, those that do often flourish.

Species like the green crab, which can tolerate a wide-range of environmental conditions and have a high reproductive rate, find themselves far away from their natural predators and well positioned to take over an area. Native species pay the price, unable to compete for food or defend themselves from these strange new inhabitants. Since arriving on the West Coast, the green crab has wiped out 90% of the Dungeness crab and other native crab populations in some areas.

In Humboldt Bay, the introduction of many invasive species can be traced to ships that import and export wood products between this region and other countries. For example, the South American cordgrass was introduced 100 years ago when redwood lumber was being exported to Chile and Peru. This species does not go dormant in the winter like native plant species, and with this and other competitive advantages it has over native plants, the cordgrass has become the dominant salt marsh plant in Humboldt Bay.

There are also two recent arrivals of amphipods (small crustaceans such as beach fleas and sand hoppers) from New Zealand and Japan, where whole logs and wood chips are traded today.

However, the risk of introduction is no longer limited to ships that travel to faraway places. More than 230 invasive species are now established in San Francisco Bay, with 100% of the species being non-indigenous in some areas. As the report from Humboldt State explained:

"Ships routinely enter Humboldt Bay after taking on a hold cargo at port facilities in San Francisco Bay and then visit…Humboldt Bay to take on a deck cargo of logs or lumber. These vessels usually take in ballast water while in San Francisco Bay and discharge some ballast water when the deck cargo has been loaded in Humboldt Bay. Such ballast water transport in intracoastal trade can rapidly spread [invasive species] along an entire continental coastline…." (Boyd, et. al, 2002)

Growing economic and ecological concerns surrounding invasive species in U.S. coastal waters led to the recent enactment of legislation at both the state and national level. The National Invasive Species Act establishes voluntary reporting and ballast water disposal methods for boats traveling into U.S. waters from international boundaries; the California Ballast Water Management Act is similar but makes reporting and disposal methods mandatory. However, both laws only pertain to international shipping traffic and do not address invasive species introduction through intrastate and interstate shipping. EPIC is exploring ways to address this increasing problem in the coming year.

Exotic Facts:

Exotic species invasions have contributed to the decline of 42% of the endangered and threatened species in the nation.

After habitat destruction, invasive species are considered the greatest cause of the loss of biological diversity.

In San Francisco Bay, an invasive species was established once every 14 weeks between 1961 and 1995.

In the Mississippi drainage basin, biological diversity is expected to decline by 50% within a decade because of the introduced zebra mussel.

Location and date the green crab was discovered on the West Coast:

San Francisco Bay, California: 1989
Bodega and Tomales Bays, California: 1994
Humboldt Bay, California: 1995
Coos Bay, Oregon: 1996
Wallapa Bay & Grays Harbor, Washington: 1998


This article can be found online at www.wildcalifornia.org/publications/article-7