Chesapeake Bay Introduced Species Database


Ascophyllum nodosum

Common name(s):
Knotted Wrack
Knotted Wrack is seaweed (algae) that attaches to rocks and other hard shoreline habitats or just floats around in the surf. It grows on both coasts of the North Atlantic and is common on rocky shores from Portugal to the White Sea in Europe, on the coasts of Iceland and Greenland, and from Baffin Island to Delaware. Floating plants have been collected in the eastern Atlantic off the coast of Ghana just south of the equator and in the Chesapeake Bay region. Seaweed collected along the coastline was likely carried in from the North in currents through natural dispersal. But because Knotted Wrack is widely used as a packing material for baitworms shipped from the Maritime provinces of Canada and New England, it probably also arrived through discarded bait. The seaweed is commonly dumped on the shore or water by fisherman and is the most probable mechanism for introduction to upper Chesapeake Bay.
Image courtesy of Grisetang fra Høgsfjord i Ryfylke, Wiki Commons.

Chesapeake Bay Status:

First Record
Population
Range
Introduction
Residency
1946
Unknown
Stable
Native & Introduced
Regular Resident

Source Region
Native Region
Western Atlantic AmphiAtlantic

Vector(s) of Introduction
Fisheries(Packing Material-Bait)


History of Spread:

Ascophyllum nodosum is a seaweed 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 DE (Baardseth 1970; South and Tittley 1986; Taylor 1957; Zaneveld 1972). This species also occurs in unattached form, 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 (Humm 1979; Zaneveld and Willis 1976).

Ascophyllum nodosum is widely used as a packing material for baitworms shipped from the Maritime provinces of Canada and New England. The seaweed is commonly dumped on the shore or water by fisherman (Cohen and Carlton 1995; Orris 1970). This is the probable mechanism for introduction of the seaweed to upper Chesapeake Bay (Orris 1980), and Hood Canal WA (Pacific), and a potential source for introductions to other locations, especially on the Pacific coast (Cohen and Carlton 1995). Living populations have been found in San Francisco Bay, and in at least once case, successfully eradicated (Miller et al. 2002).

In the Chesapeake region and southward to Cape Hatteras, 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 1976) and probably occur in the Chesapeake region, but appear to be quite rare. ' A. nodosum has been found in the Bay but the meaning of its presence in the upper Bay is a subject for speculation and controversy. There are a dozen or more specimens in the herbarium (MARY) (=University of Maryland) or mentioned by Zaneveld and Willis (1976). These probably represent bait-packing material thrown overboard by fishermen rather than an endemic population of A. nodosum in the upper Bay. Several facts and observations support this conclusion: (1) blood worms are shipped from MA to the Delmarva region packed in A. nodosum (2) specimens are usually found floating or washed ashore near popular fishing spots, i.e. bridges, state parks, and harbors, (3) I have seen fishermen throwing Ascophyllum overboard near the Chesapeake Bay bridge, and (4) I have never seen Ascophyllum in marshes along the upper Bay and its tributaries' (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 an herbarium specimen collected from Virginia Beach VA in 1946 (Zaneveld and Willis 1976), but that probably just reflects limited collecting activity in the region.

Chesapeake records are summarized below:

Atlantic Coast - Ocean City MD, 'attached to the North Jetty', and 'abundant in the wash' (forma scorpioides), 1971 (Ott 1973); Assateague MD, 1955 (Zaneveld and Willis 1976); Chincoteague Inlet VA (Ott 1973); (Northampton County VA (near Hog Island), 1960; Fisherman's Island 1962; 'Seaside Park',Virginia Beach VA, 1946 (Zaneveld and Willis 1976). These records probably represent both introduced and naturally dispersed plants.

Lower Bay - Norfolk VA, 1962 (Zaneveld and Willis 1976); Pocomoke Sound MD (Krauss et al. 1971). These records probably represent both introduced and naturally dispersed plants.

Upper Bay - Patuxent River estuary, drifting (Anderson et al. 1968); Baltimore County MD, 1960, drifting; Sandy Point State Park (Anne Arundel County) MD, 1955, drifting (Zaneveld and Willis 1976).

West Coast- In San Francisco Bay, floating bunches of Ascophyllum nodosum have frequently been found (Miller 1969), usually of 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 on South San Francisco Bay. 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 bait-worms imported from New England or Atlantic Canada (Miller et al. 2005). The plants were eradicated by manual picking, and disposed in a landfill. No A. nodosum were 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. Ateempts 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, Puget Sound, but the establishment of this seaweed there is unknown (Linda Goff, personal communication, cited by Cohen and Carlton 1995.)

History References - Anderson et al. 1968; Baardseth 1970; Cohen and Carlton 1995; Humm 1979; John 1974; Krauss et al. 1971; Miller et al. 2002; Orris 1980; Ott 1973; Schneider and Searles 1991; South and Tittley 1986; Taylor 1957; Zaneveld 1972; Zaneveld and Willis 1976



Invasion Comments:

Invasion Status - Ascophyllum nodosum occurs as both naturally occcuring plants (mostly along the Atlantic coast), and as introduced plants in bait packing material, which are probably dumped into waters throughout the region. Upper Bay occurrences are presumed to be exclusively due to introductions (Orris 1980), while lower Bay and coastal occurrences may consist of both introduced and naturally dispersed plants. Drifting A. nodosum can reproduce vegetatively, but seems to have only limited sexual reproduction (Chock and Mathieson 1979). 'It seems strange that in Virginia waters drifting plants do not produce viable embryos that would become attached, especially in the vicinity of Chincoteague Island (Humm 1979). In the upper Bay, A. nodosum is probably unable to reproduce at all, due to low salinities and high summer temperatures (Orris 1980).



This data was last modified on Tuesday, April 10th, 2012.
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