Ascophyllum nodosum

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:

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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).

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Description

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).

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Taxonomy

Ecology

General:

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

PrimProd

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Habitats

General Habitat	Salt-brackish marsh	None
General Habitat	Unstructured Bottom	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Tidal Range	Mid Intertidal	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	-1.8	Based on geographical range, in areas with winter sea ice
Maximum Temperature (ºC)	26	40% survival for 60 days, 100% survival at 23 C (Wilson et al. 2015)
Minimum Salinity (‰)	10	Field data, Baardseth 1970
Maximum Salinity (‰)	37	Field data, Baardseth 1970
Minimum Reproductive Salinity	15	Field data, Baardseth 1970
Maximum Reproductive Salinity	37	Field data, Baardseth 1970
Broad Temperature Range	None	Polar-Warm temperate
Broad Salinity Range	None	Mesohaline-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.

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References

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