Spotlight – Invasive Species in the Nearshore

Non-native and invasive species are a concern for Oregon’s estuaries and nearshore waters. Non-native species arrive in a variety of ways including release of animals kept as pets, escapes from aquaculture facilities, intentional introduction, hitchhiking on boats or recreational equipment, seafood packing and disposal, and perhaps most importantly, ballast water. International shipping (including its ballast water component), followed by aquaculture, have been identified as the two greatest sources of introductions of marine and estuarine invasive species worldwide. Ship ballast water is known to carry viable organisms from one body of water to another, and it is estimated that over two-thirds of recent species introductions in marine and coastal areas are likely due to this ship-borne vector.

One well-documented invasion in Oregon is the Griffen’s isopod (Orthione griffenis), native to Asia and likely introduced via ship ballast water during the 1980s. This parasitic isopod can draw enough blood from the native blue mud shrimp (Upogebia pugettensis) to prevent it from reproducing. The introduction of this parasite has been linked to substantial population declines of blue mud shrimp in many Pacific Northwest estuaries.

Another well-documented invasion is the European green crab (Carcinus maenas), native to the northeast Atlantic and Baltic Sea coasts, which was first seen in San Francisco Bay in 1989. European green crab larvae can survive for up to 80 days in coastal waters and then return to adjacent bays and estuaries to settle. The expansion of European green crab from San Francisco Bay likely occurred on coastal currents south to Monterey Bay and northward to Humboldt Bay, California. The spread to Coos Bay and Yaquina Bay, Oregon, Willapa Bay and Grays Harbor, Washington, and the west coast of Vancouver Island occurred following the strong El Niño of 1997/1998. The expansion of European green crab up the east coast of the U.S. to Maine occurred over an approximately 120-year period, culminating in the collapse of the soft-shell clam industry in Maine. European green crab could possibly threaten Dungeness crab, oyster and clam fisheries, and aquaculture operations in the Pacific Northwest.

Estuaries are especially susceptible to adverse impacts from invasive plants and animals. Coastal ocean conditions are critical determinants of biological invasions of estuaries, but the processes and possible management strategies for limiting ocean dispersal of invasive species are unknown. In estuaries, invasive plants can alter water circulation and sediment patterns. For example, common cordgrass (Spartina anglica), which has been documented in two Oregon estuaries and is well-established in Washington and California, reduces mud flat habitats, disrupts nutrient flows, displaces native plants and animals, and traps sediments, which changes the beach profile and water circulation. Three other cordgrass species have invaded the Pacific coast and could potentially pose a threat to estuaries.

Within the nearshore ecoregion, an effort by conservation partners in Oregon was initiated in 2012 to assess existing or potential threats to marine and estuarine ecosystems. ODFW developed a list of non-native species known to occur in the nearshore waters of Oregon and neighboring states, in consultation with Oregon State University (OSU), the Environmental Protection Agency (EPA) Western Fisheries Research Center, USGS, and Williams College. This information was last updated in 2015. At that time, more than 200 non-native species had been identified in Oregon marine and estuarine waters, of which 14 were classified as invasive (see Appendix – Nearshore Species).