Nonnative Species Spell Trouble for Puget Sound

Lauren Mulroy is a graduate of Huxley College and served as a RE Sources intern. Robyn du Pré served as the North Sound Baykeeper and coordinated water programs at RE Sources for eight years. She currently teaches field-based environmental studies for the Audubon Expedition Institute.

Editor’s Note: This is the fifth in a multipart series on the health of northern Puget Sound and Georgia Strait. It was first published under the title, “State of the North Sound and Straits,” by RE Sources and the North Sound Baykeeper in October 2002.

New species entering the marine environment of the north Puget Sound and Straits pose a growing threat to ecosystem health. Often these invaders come without the natural predators with which they co-evolved in their native ecosystems, and can quickly dominate a new system. The impacts of nonnative, or exotic, species moving into and becoming established in a new ecosystem are difficult to predict. While some are seemingly harmless, others can have catastrophic effects.

Impacts from invasive species can include: increased predation upon native species, competition with native species for the same food sources or habitats, changing the nature of the habitat itself, the introduction of new parasites into the system, and interfering with human infrastructure.

In the year 2000 alone, 10 non-indigenous species were found that had not been previously reported in Puget Sound. These discoveries increased the number of known nonnatives in area salt and brackish waters to 56 species. Two exotic species of concern here in the north Sound and Straits are the cord grasses, Spartina spp, and the European green crab, Carcinus maenus.

Spartina alterniflora is a perennial marsh grass that severely disrupts native saltwater ecosystems, alters fish, shellfish and bird habitat and increases the threat of floods. Spartina transforms productive mudflats into marshy areas, trapping sediments and changing the elevation so that the area is often no longer intertidal.

This can be particularly problematic for migrating shorebirds and waterfowl that rely on mudflat habitat for feeding and resting while on their journey along the Pacific flyway. As well, it can rob the estuary of important nursery habitat for small fishes, and make the area unsuitable for clams and oysters.

Local infestations of Spartina are known to occur along the Strait of Juan de Fuca and in numerous areas along the shorelines of Skagit County. These have been small to medium infestations, allowing for effective control efforts.

Spartina covered approximately 17 acres in Padilla Bay, but eradication efforts have brought the infestation down to less than one-half acre. Eradication efforts in Padilla Bay have included hand digging and pulling by volunteers, cutting off the tops before the seeds mature and limited spraying of herbicide.

Spartina occurs in various locations along the shorelines of Skagit County, including a notable infestation in Alice Bay. The nonnative marsh grass has not yet been found in Whatcom County waters, but the rich, shallow mudflats of the Nooksack River delta are prime habitat.

As of the beginning of 1999, control efforts of the Washington Department of Agriculture and its partners have significantly reduced the size of Puget Sound Spartina infestations. As smaller, outlying populations of this weed are reduced or eliminated, larger areas of infestation, such as South Skagit Bay, will become a bigger priority.

• It is a striking grass, growing in roundish clumps 2-6 feet tall.

• It grows in the intertidal zone along saltwater shores.

• Its leaf blades are 1/4 to 2/3 inches wide and branch from the smooth stem at a steep angle.

• When the leaf is pulled down and off the stem, the ligule (the joint where the leaf meets the stem) is somewhat hairy.

Local residents are encouraged to call their local Noxious Weed Board if Spartina is suspected in any local estuary.

One invasive species that has not yet been sighted in local waters, but is of great concern to biologists, is the European green crab Carcinus maenas. A federally recognized nuisance species, it first appeared on Washington’s coast in June 1998. A relatively small crab, this voracious predator preys upon a wide variety of plants and animals, but prefers the commercially and recreationally important clams, oysters, mussels and juvenile Dungeness crab.

Green crabs are found in water up to 30 feet deep and in the high intertidal zone and in salt marshes. To date, green crabs have not been found in the marine waters of the northern Sound and Straits, but local agencies are certainly on the lookout.

• Adult green crab measure 3" to 4" across.

• Look for five spines on either side of the front of the shell.

• Green crabs have three rounded lobes between the eyes.

• Color is deceptive, as the crab’s shell can be a variety of colors. Adults, however, are often a dark greenish color, with yellow markings on the top of the shell.

• Their undersides tend to be bright red or yellow.

If you sight what you suspect to be European green crab, make note of the time, date and location of the sighting. Do not try to trap the crab, as it is illegal to possess or transport live specimens. Contact the Washington Department of Fish and Wildlife to report the sighting. §

Next Month: Shoreline Modification and Toxics in the Marine Environment