NEMESIS Bioregion Distribution:

Native  Introduced  Cryptogenic  Failed

First Non-native North American Marine/Estuarine Record: 1992
First Non-native West Coast Marine/Estuarine Record: 1992

General Invasion History:

Ascophyllum nodosum is found on both coasts of the North Atlantic. Attached plants occur regularly on rocky shores from Portugal to the White Sea in Europe, on the coasts of Iceland and Greenland, and from Baffin Island to Delaware in North America (Taylor 1957; Baardseth 1970; Zaneveld and Willis 1974; South and Tittley 1986). This species also occurs in unattached forms, entangled among marsh vegetation, lying on mudflats, or freely drifting at the ocean surface ('ecad' or var. scorpioides or mackai). Unattached A. nodosum have been collected in the eastern Atlantic off the coast of Ghana just south of the equator, probably derived from western European populations (John 1974). Most reports of A. nodosum from the Chesapeake Bay region are of unattached plants (Zaneveld and Willis 1974; Humm 1979).

Ascophyllum nodosum is widely used as packing material for baitworms shipped from the Maritime Provinces of Canada and New England. The seaweed is commonly dumped on the shore or in water by fisherman (Orris 1980; Cohen and Carlton 1995). It is also commonly used to pack lobster and other shellfish shipped from the Atlantic Coast, and may often be dumped on the shore near waterfront restaurants and shellfish markets (Miller 1969). This is the probable mechanism for introduction of the seaweed to upper Chesapeake Bay (Orris 1980), and Hood Canal, Washington (Pacific), and a potential source for introductions to other locations, especially on the Pacific coast (Cohen and Carlton 1995).

North American Invasion History:

Invasion History on the West Coast:

In San Francisco Bay, California, floating bunches of Ascophyllum nodosum were found as early as 1966 (Miller 1969). These were usually the attached form of the plant, A. nodosum ecad scorpiodes, and often in deteriorating condition. In September 2002, a small patch of healthy A. nodosum was discovered during a survey of San Francisco Bay, near the Redwood City marina. The form of A. nodosum was ecad mackayi, a growth form which grows entwined around salt-marsh vegetation. It was probably introduced with seaweed used to wrap baitworms imported from New England or Atlantic Canada (Miller et al. 2004). The plants were eradicated by manual picking and disposed in a landfill. No A. nodosum have been seen at this site since December 2002. More recently, in 2008, growing A. nodosum was seen on the shores of Bay Farm Island, Alameda, CA. Attempts at removal have been made, but whether it has been eradicated is unknown (Whitman Miller, personal communication). Ascophyllum nodosum has also been seen in Hood Canal, Washington, but the establishment status of this seaweed is unknown (Linda Goff, personal communication, cited by Cohen and Carlton 1995).

Invasion History on the East Coast:

In the Chesapeake Bay region and southward to Cape Hatteras, North Carolina, A. nodosum occurrences appear to consist both of naturally dispersed unattached plants, carried by the currents southward along the Atlantic coast (Humm 1979) and plants dispersed by human activities (Orris 1980; Searles 1997). Attached plants are known from Cape Hatteras (Schneider and Searles 1991; Zaneveld and Willis 1974) and may occur in the Chesapeake region, but appear to be quite rare. Ascophyllum nodosum has been found in the Chesapeake Bay but its establishment is unknown. There are a dozen or more specimens in the University of Maryland herbarium or mentioned by Zaneveld and Willis (1974); however, it’s possible that these represent bait-packing material thrown overboard by fishermen rather than an endemic population of A. nodosum (Orris 1980). Searles (1997) mentions lobsters as another commodity shipped in seaweed from New England which probably also contributes to records of A. nodosum around Cape Hatteras, and doubtless also in the Chesapeake region. The earliest published date for A. nodosum in the Chesapeake region is a herbarium specimen collected from Virginia Beach, VA in 1946 (Zaneveld and Willis 1974).

Invasion History elsewhere in the World:

In the Mediterranean Sea, attached thalli of Ascophyllum nodosum were found in the Mar Piccolo, Taranto, Italy, attached to pebbles and fishing nets, in an area near seafood shops where mussels were sold. It is not established, but is periodically introduced with shellfish shipments (Petrocelli et al. 2013).