Invasion History

First Non-native North American Tidal Record: 1992
First Non-native West Coast Tidal Record: 1992
First Non-native East/Gulf Coast Tidal Record:

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).


Ascophyllum nodosum is a large brown seaweed found on intertidal and subtidal rocks, usually in sheltered waters. Morphological variants occur in salt marshes, mudflats, and occasionally floating in plankton. The plant has a leathery, narrow, branched, linear thallus, lacking a midrib, marked by numerous inflated vesicles, also known as floats (generally ~20-30 mm long,~ 20 mm wide). The plant is often attached by a discoid holdfast, but can be free-floating or entangled with other plants. The pattern of primary branching is dichotomous, while secondary branching is bilateral, with short, forked or club-like branchlets, 1-2 cm long. The plants are dioecious, developing receptacles, which begin first as linear structures and expand to a globular shape when mature. Plants grow to 600 mm and sometimes over 1000 mm. The color is usually olive-green, but can range from yellow to brown. Description based on: Baardseth 1970, Gosner 1978, and Schneider and Searles 1991.

An unattached form of A. nodosum has been distinguished from the attached form as separate species ('scorpioides' or 'mackaii') (e.g. Taylor 1957) or as a variety or ecotype ('forma'; 'ecad', etc.) (South and Hill 1970; Chock and Mathieson 1979). These forms tend to have flattened and very dichotomous (branched) thalli, and tend to lack air bladders and receptacles (sexual organs) (Gibb 1957; South and Hill 1970). The 'ecad' or ecotype interpretation seems to be more common in recent literature (e.g. Chock and Mathieson 1979). Gradients among morphotypes occur in marshes (Brinkhuis 1976; Chock and Mathieson 1979) and frond fragments from the 'scorpiodes ' ecad will take on the morphology of the drifting 'mackai' ecad when transplanted to the lower intertidal (Brinkhuis and Jones 1976). The frequency of sexual reproduction is greatly reduced in these forms, but a portion of the sexual offspring produced are attached. In addition to this distinction, additional morphological differentiation probably exists. 'There can be no doubt that genetically differentiated races of Ascophyllum exist, and in large numbers' (Baardseth 1970).


Taxonomic Tree

Kingdom:   Plantae
Phylum:   Phaeophycophyta
Class:   Phaeophyceae
Order:   Fucales
Family:   Fucaceae
Genus:   Ascophyllum
Species:   nodosum


Ascophylla laevigatum ( Stackhouse, 1809)
Ascophyllum nodosum var. mackayi ((Turner) Cotton, 1912)
Ascophyllum nodosum var. scorpioides ((Hauck) Reinke, 1889)
Fistularia mackayi (Turner) (Stackhouse, 1816)
Fistularia nodosa (Linnaeus) (Stackhouse, 1816)
Fucus mackayi (Turner, 1808)
Fucus nodosus (Linnaeus, 1753)
Fucus nodosus var. siliquatus (Turner, 1802)
Fucus scorpioides (Hornemann, 1813)

Potentially Misidentified Species



Ascophyllum nodosum is a large brown seaweed found on intertidal and subtidal rocks, usually in sheltered waters. Morphological variants occur in salt marshes, mudflats, and occasionally floating in the plankton. Plants can reproduce asexually by basal shoots or by lateral shoots from fragments. Sexual reproduction takes place by eggs or sperm produced in conceptacles, which mature in winter or spring. The plants are dioecious (single-sexed). Egg or sperm release can happen after air exposure or by agitation of the water. Fertilized zygotes settle within 10 days, and become germlings, attached by a rhizoid. However, asexual reproduction is much more important than sexual reproduction in A. nodosum (Baardseth 1970; Bold and Wynne 1978).

Ascophyllum nodosum, in regions with tides, grows primarily in the intertidal zone and in shallow water (<0. 5 m) in areas with minimal tides (Baardseth 1970). It is most abundant in cold climates and reaches its southern limits in areas where average summer temperatures rise above 22°C, although it can tolerate temperatures up to 26°C for shorter periods (Baardseth 1970; Wilson et al. 2015). Attached plants do not occur in the Baltic, but free-living forms occur as far east as Kiel Bay, at salinities as low as 10-15 PSU (Baardseth 1970; South and Tittley 1986). Ascophyllum nodosum require bedrock or stable stones for attachment (Baardseth 1970). Free-living forms, such as the ecads mackayi or scorpioides grow entangled around Spartina spp., or other marsh vegetation (Brinkhuis 1976; Chock and Mathieson 1979). The role of genetics versus environment in the morphology of the ecads is unclear. Brinkhuis and Jones (1976) suggest that unattached ecad populations form from 'normal' A. nodosum drifting into the marshes.

Trophic Status:

Primary Producer



General HabitatSalt-brackish marshNone
General HabitatUnstructured BottomNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Tidal RangeMid IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)-1.8Based on geographical range, in areas with winter sea ice
Maximum Temperature (ºC)2640% survival for 60 days, 100% survival at 23 C (Wilson et al. 2015)
Minimum Salinity (‰)10Field data, Baardseth 1970
Maximum Salinity (‰)37Field data, Baardseth 1970
Minimum Reproductive Salinity15Field data, Baardseth 1970
Maximum Reproductive Salinity37Field data, Baardseth 1970
Broad Temperature RangeNonePolar-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

Economic Impacts

Ascophyllum nodosum is an ecologically important component of rocky shore and marsh habitats, and provides shelter and food for many intertidal invertebrates. It has long been harvested for animal fodder, fertilizer, soda and alginates, and is harvested in Eastern Canada, Ireland, Scotland, and Norway (Baardseth 1970; Guiry 2016). A major use in Maine and the Maritime provinces is as packing-material for baitworms (Alitta virens and Glycera dibranchiata) shipped worldwide with ice-packs. The seaweed is usually discarded when the worms are used and dumped on the beach or in the water. Similarly, A. nodosum has long been used, together with other East Coast seaweeds, as packing material for American Lobsters (Homarus americanus) shipped from New England or the Maritimes.

Ecological Impacts

The largest impact of A. nodosum on the West Coast is as a vector for invasive invertebrates and algae from the Northwest Atlantic. It could have been a vector for the introduction of Carcinus maenas and Littorina saxatilis to the West Coast (Carlton and Cohen 1998; Carlton and Cohen 2003). Surveys of fauna found in Ascophyllum used to pack baitworms have found a wide range of organisms, including annelids, gastropods, bivalves, ostracods, copepods, isopods, mites, and insects (Haska et al. 2011; Fowler et al. 2015). Miller (1969) found a similar range of invertebrates on A. nodosum used to pack lobsters in San Francisco restaurants. Some of the invertebrates, particularly amphipods, introduced on the West Coast, may have been transported on this seaweed.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
B-I None 0 Native Estab
NEA-V None 0 Native Estab
NA-P3 None 0 Native Estab
NA-S3 None 0 Native Estab
NA-S2 None 0 Native Estab
NA-ET1 Gulf of St. Lawrence to Bay of Fundy 0 Native Estab
NA-ET2 Bay of Fundy to Cape Cod 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 0 Native Estab
NEA-IV None 0 Native Estab
NEA-III None 0 Native Estab
NEA-II None 0 Native Estab
B-II None 0 Native Estab
NA-P2 None 0 Native Estab
WA-I None 0 Native Unk
M130 Chesapeake Bay 1955 Crypto Unk
NA-ET4 Bermuda 0 Native Unk
NEA-VI None 0 Native Unk
AR-V None 0 Native Estab
AR-IV None 0 Native Estab
AR-III None 0 Native Estab
P290 Puget Sound 1992 Def Unk
NEP-III Alaskan panhandle to N. of Puget Sound 1992 Def Unk
B-III None 0 Native Estab
B-IV None 0 Native Estab
NEP-V Northern California to Mid Channel Islands 2002 Def Unk
P090 San Francisco Bay 2002 Def Unk
MED-IV None 2012 Def Unk
CAR-VII Cape Hatteras to Mid-East Florida 1991 Crypto Unk
S030 Bogue Sound 1991 Crypto Unk

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Anderson, Richard D.; Brown, Russell, G.; Rappleye, Robert D. (1968) Water quality and plant distribution along the upper Patuxent River, Maryland, Chesapeake Science 9(3): 145-156

Baardseth, B. (1970) Synopsis of biological data on knobbed wrack Ascophyllum nodosum (Linnaeus) Le Jolis, FAO Fisheries Synopsis 38: 1-40

Bold, Harold C.; Wynne, Michael J. (1978) Introduction to the Algae: Structure and Reproduction, Prentice-Hall, Englewood Cliffs, NJ. Pp. <missing location>

Brinkhuis, I. H.; Jones, R. F. (1976) The ecology of temperate salt-marsh fucoids. In situ growth of transplant Ascophyllum nodosum ecads, Marine Biology 34: 339-348

Brinkhuis, J. H. (1976) The ecology of temperate salt-marsh fucoids. I. Occurrence and distribution of Ascophyllum nodosum ecads, Marine Biology 34: 325-338

Carlton, James T., Cohen, Andrew N. (1998) Periwinkle's progress: the Atlantic snail Littorina saxatilis (Mollusca: Gastropoda) establishes a colony on a Pacific shore, The Veliger 41(4): 333-338

Carlton, James T.; Cohen, Andrew N. (2003) Episodic global dispersal in shallow water marine organisms: the case history of the European shore crabs, Carcinus maenas and C. aestuarii, Journal of Biogeography 30: 1809-1820

Chock, J. S.; Mathieson, A. C. (1979) Physiological ecology of Ascophyllum nodosum (L.) Le Jolis and its detached ecad scorpioides (Hornemann) Hauck (Fucales, Phaeophyta), Botanica Marina 22: 21-26

Chock, Jay S. (1976) Ecological studies of the salt marsh ecad scorpioides (Hornemann) Hauck of Ascophyllum nodosum, (L.) Le Jolis, Journal of Marine Biology and Ecology 23: 171-190

Cohen, Andrew N.; Carlton, James T. (1995) Nonindigenous aquatic species in a United States estuary: a case study of the biological invasions of the San Francisco Bay and Delta, U.S. Fish and Wildlife Service and National Sea Grant College Program (Connecticut Sea Grant), Washington DC, Silver Spring MD.. Pp. <missing location>

Fernandez-Alvarez, Fernando Angel Machordom, Annie (2012) DNA barcoding reveals a cryptic nemertean invasion in Atlantic and Mediterranean waters, Helgoland Marine Research 67: 599-605
DOI 10.1007/s10152-013-0346-3

Fowler, Amy E. and 8 authors (2015) Opening Pandora’s bait box: a potent vector for biological invasions of live marine species, Diversity and Distributions 22: 30-42

Gibb, Dorothy C. (1957) The free-living forms of Ascophyllum nodosum (L.) Le Jol., Journal of Ecology 45: 49-83

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Guiry, M. D.; Guiry, G. M. 2004-2023 AlgaeBase. National University of Ireland Galway--

Guiry, M.D. 1998-2016 Seaweed Site. An internet accessible taxonomic database on seaweeds, primarily of Europe; referenced in the AK report-

Haska, Christina L. and 6 authros (2011) Bait worm packaging as a potential vector of invasive species, Biological Invasions 13: published online

Humm, Harold J. (1979) The Marine Algae of Virginia, University Press of Virginia, Charlottesville. Pp. <missing location>

John, David M. (1974) New records of Ascophyllum nodosum (L.) Le Jol. from the warmer parts of the Atlantic Ocean, Journal of Phycology 10: 243-244

Josselyn, Michael N.; West, John A. (1985) The distribution and temporal dynamics of the estuarine macroalgal community of San Francisco Bay, Hydrobiologia 129: 132-152

Larsen, Peter Foster (2012) The macroinvertebrate fauna of rockweed (Ascophyllum nodosum) dominated low-energy rocky shores of the northern Gulf of Maine, Journal of Coastal Research 28(1): 36-42

Locke, Andrea; Hanson, John Mark; MacNair, Neil G.; Smith, Arthur H. (2009) Rapid response to non-indigenous species. 2. Case studies of invasive tunicates in Prince Edward Island, Aquatic Invasions 4(1): 249-258

Locke, Andrea; Hanson, John Mark (2009) Rapid response to non-indigenous species. 1. Goals and history of rapid response in the marine environment., Aquatic Invasions 4(1): 237-247

Miller, A. Whitman ; Chang, Andrew L.; Cosentino-Manning, N.; Ruiz, Gregory M. (2004) A new record and eradication of the northern Atlantic alga Ascophyllum nodosum (Phaeophyceae) from San Francisco Bay, California., Journal of Phycology 40: 1028-1031

Miller, Kathy Ann; Aguilar-Rosas, Luis Ernesto; Pedroche, Francisco F. (2011) A review of non-native seaweeds from California, USA and Baja California, Mexico, Hidrobiológica 21(3): 365-379

Miller, Richard (1969) Ascophyllum nodosum: A source of exotic invertebrates introduced into West Coast near-shore marine waters, Veliger 12(2): 230-231

Orris, Patricia K. (1980) A revised species list and commentary on the macroalgae of the Chesapeake Bay in Maryland, Estuaries 3(3): 200-206

Ott, Franklyn D. (1973) The marine algae of Virginia and Maryland including the Chesapeake Bay area, Rhodora 75(802): 258-296

Petrocelli, Antonella; Cecere, Ester; Verlaque, Marc (2013) Alien marine macrophytes in transitional water systems: new entries and reappearances in a Mediterranean coastal basin, BioInvasions Records 2: in press

Schneider, Craig W.; Searles, Richard B. (1991) Seaweeds of the Southeastern United States Cape Hatteras to Cape Canaveral, Duke University Press, Durham. Pp. <missing location>

Searles, Richard B. March 21, 1997 Introduced seaweeds in Chesapeake Bay, email. Department of Botany, Duke University

Silva, Paul C. (1979) San Francisco Bay Bay: The urbanized estuary; Investigations into the Natural History of San Francisco Bay and Delta With Reference to the Influence of Man, Pacific Division of the American Association for the Advancement of Science, San Francisco. Pp. 287-346

South, G. R.; Hill, R. D. (1970) Studies on marine algae of Newfoundland. I. Occurrence and distribution of free-living Ascophyllum nodosum in Newfoundland, Canadian Journal of Botany 48(10): 1697-1701

South, G. Robin; Tittley, Ian (1986) <missing title>, Huntsman Marine Laboratory and British Museum (Natural History), St. Andrews, New Brunswick, and London. Pp. <missing location>

Taylor, William Randolph (1957) Marine Algae of the Northeastern Coast of North America, University of Michigan Press, Ann Arbor. Pp. <missing location>

Van Patten, Margaret Stewart (2006) Seaweeds of Long Island Sound, Connecticut Sea Grant, Groton. Pp. <missing location>

Wilson, Kristen L.; Kay, Lauren M.; Schmidt, Allison L.; Lotze, Heike K. (2015) Effects of increasing water temperatures on survival and growth of ecologically and economically important seaweeds in Atlantic Canada: implications for climate change, Marine Biology 162: 2431-2444

Zaneveld, Jacques, Willis, William M. (1974) The marine algae of the American coast between Cape May, New Jersey, and Cape Hatteras, North Carolina. II. The Chlorophycota, Botanica Marina 17(2): 65-81