Taxonomic name: Codium fragile ssp. tomentosoides (van Goor) P.C. Silva
Synonyms: Codium mucronatum var. tomentosoides van Goor
Common names: dead man's fingers, green fleece, green sea fingers, oyster thief, Sputnik weed
Organism type: alga
Codium fragile ssp. tomentosoides is an alga that has been introduced around the globe through shellfish aquaculture, recreational boating, and transport on ship hulls. The species fouls shellfish beds and causes a myriad of impacts on shellfish communities. This species also causes a nuisance to humans when it accumulates on beaches and rots producing a foul odor. C. fragile ssp. tomentosoides has been documented altering benthic communities and habitats causing serious environmental implications.
Trowbridge (1999) reports that, "C. fragile ssp. tomentosoides is a large branching species that can reach lengths of 1 metre and can weigh up to 3.5kg. The alga has up to ten orders of dichotomous branching; the cylindrical or terete branches are 3-10mm in diameter (Trowbridge 1998a). Fronds arise out of either a spongy, basal holdfast or a vaucherioid mat. Differentiated macroscopic thalli are formed by the interweaving of siphonous filaments that compose two regions of the thallus. The central region (medulla) is composed of long, colourless filaments (medullary filaments) that run longitudinally within the thallus and are densely intertwined. These vary in size among different subspecies but are typically 26-68 µm in diameter (Trowbridge 1998a). The peripheral region (cortex) is formed of cylindrical or club-shaped siphonous swellings called utricles that are tightly compressed together." Hubbard and Garbary (2002) state that the medullary filaments are surrounded by the utricles and that, "The utricles, which are the swollen cortical tips of the filaments, typically have mucrons (i.e. colourless, spine-like to rounded terminal cell wall projections), colourless hairs and gametangia."
coastland, estuarine habitats, marine habitats
Begin and Scheibling (2003) state that, "C. fragile ssp. tomentosoides tolerates large variations in salinity and temperature, enabling it to colonise a wide range of environments. This species appears to thrive in sheltered habitats such as harbors and bays, which may facilitate its transport by human activities. Our study shows that this invasive alga also survives and grows in tide pools on wave-swept intertidal shores. C. fragile occurs at relatively high density in low and mid zone pools." These species also accumulates profusely on wharf pilings, jetties, ropes, and beaches (Trowbridge, 1999).
Begin and Scheibling (2003) have found that the invasive success of C. fragile ssp. tomentosoides in the northwest Atlantic can be attributed to various characteristics of the alga's life history and physiological ecology. This species exhibits various modes of reproduction, which is a common trait in many invaders. It can reproduce sexually, parthenogentically, and vegetatively. Water currents can and will carry this species over long distances introducing it to new locations. C. fragile is also tolerant of a variety of salinity and water temperature levels. It also thrives in sheltered habitats, which facilitate human mediated dispersal (Begin and Scheibling, 2003).
Provan et al. (2005) state that, "C. fragile ssp. tomentosoides has serious economic implications for aquaculture industries. Indeed, the tendency of this species to overgrow and smother oyster beds has earned it the nickname 'oyster thief' (Naylor et al. 2001)." The Benthic Ecology Lab (2001) adds that it has found that, "In its quest for a stable substrate C. fragile ssp. tomentosoides will often make its home on the shells of oysters, scallops, and clams. This can cause problems because an attached adult plant can hinder the movement and feeding of the shellfish. In cases where the attached plant is relatively large and wave exposure is high, the shellfish can be swept away with the plant."
Trowbridge (1999) reports that, "The most detrimental effect of C. fragile ssp. tomentosoides is the fouling of shellfish beds, particularly on NW Atlantic shores. There are several direct and direct effects of this attachment (Trowbridge 1998a); these include: 1) smothering mussels and scallops by preventing opening of the valves, clogging scallop dredges, and interfering with the collecting of clams. C. fragile ssp. tomentosoides also is a fouling agent of nets of fin and squid fishers increasing labor costs during harvesting and processing associated with the need to remove the alga from shellfish and the replacement of nets. The authors also state that, "The main negative social effect is that the introduced alga grows profusely and fouls wharf pilings, jetties, ropes, and beaches thereby reducing the amenity associated with the use of coastal areas. Furthermore, the accumulation of masses of C. fragile ssp. tomentosoides rotting on beaches of the NW Atlantic, Mediterranean, and New Zealand produces a foul odor that drives away visitors."
The Benthic Ecology Lab (2001) states that, "The morphological structure of C. fragile ssp. tomentosoides will likely increase sedimentation. C. fragile ssp. tomentosoides is a "low lying" alga, making it difficult for some large invertebrates and fish to move among the plants and live in the space between the bushy parts of the algae and the seabed (the understory). In a kelp bed, many species can freely move under the canopy of fronds because the stems (stipes) are narrow and widely spaced. They rely on this understory environment for food, habitat and protection from predators. Replacement of kelp by C. fragile ssp. tomentosoides will undoubtedly affect such species."
Trowbridge (1999) reports that, "C. fragile is currently recognised as a single species with morphologically (i) homogeneous populations considered subspecies, and (ii) heterogeneous populations referred to just as C. fragile. Two of the six described subspecies are currently recognised as introduced and a third subspecies may be introduced (Silva 1955, 1957). One of these subspecies, ssp. tomentosoides is among the most invasive seaweeds in the world, with extensive trans-oceanic and inter-oceanic spread this century (reviewed by Carlton and Scanlon 1985, Ribera 1994, Verlaque 1994, Trowbridge 1995, 1998a, Trowbridge and Todd 1999)." Hubbard and Garbary (2002) add that, "There are six described subspecies of C. fragile, the diagnostic features of which are the size and shape of the utricles, especially the mucron. Less reliable diagnostic characters include length and thickness of the thallus and frond flatness below dichotomies. Of the six subspecies of C. fragile, only ssp. scandinavicum Silva, ssp. atlanticum (Cotton) Silva and ssp. tomentosoides (Van Goor) Silva are considered invasive."
Begin and Scheibling (2003) believe that, "The success of C. fragile ssp. tomentosoides in colder waters north of Cape Cod, in regions previously considered unsuitable for this species, suggests a new ecotype along the northern extent of its range."
Native range: Asian Pacific Region (Provan et al. 2005).
Known introduced range: Africa, Australasia-Pacific region, Europe, North America, and South America (Begin and Scheibling, 2003; Trowbridge, 1999; Provan et al. 2005; and Begin and Scheibling, 2003).
Introduction pathways to new locations
Aquaculture: Codium fragile dispersal was probably aided by human activities such as boating or shellfish aquaculture (Coffin and Stickney 1967) (Begin and Scheibling, 2003).
C. fragile has been known to be introduced through oysters. The alga arrives attached to the oysters (Trowbridge, 1999).
Ship/boat hull fouling: Codium fragile was first reported in the northwest Atlantic at Long Island Sound in 1957, presumably introduced by ships from Europe (Bouck and Morgan 1957) (Begin and Scheibling, 2003).
Ship hulls are considered a likely vector of C. fragile (Trowbridge, 1999).
Local dispersal methods
Water currents: Water currents can and will carry this species over long distances introducing it to new locations (Begin and Scheibling, 2003).
There are few options available to manage C. fragile ssp. tomentosoides. Chemical herbicides are not a viable option of control and end up doing harm. Mechanical removal techniques such as trawling, cutting, and suctioning may reduce density temporarily, but they are expensive and the populations will quickly rebound. Manual removal will not work either. C. fragile ssp. tomentosoides readily reproduces from fragments. There are a variety of naturally occurring organisms that feed on C. fragile ssp. tomentosoides but no one or combination of species can offer sufficient control these species do not readily discriminate between the native and introduced C. fragile subspecies. Preventing the spread of C. fragile ssp. tomentosoides through quarantine measures and public education are some of the only ways to insure it does not become spread (Trowbridge, 1999).
A two year study was undertaken for the Department of Environment and Heritage (Australia) by the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to identify and rank introduced marine species found within Australian waters and those not found within Australian waters.
All of the non-native potential target species identified in this report are ranked as high, medium and low priority, based on their invasion potential and impact potential. C. fragile tomentosoides is identified as one of ten most damaging potential domestic target species, based on overall impact potential (economic and environmental). A hazard ranking of potential domestic target species based on invasion potential from infected to uninfected bioregions identifies C. fragile tomentosoides as a 'medium priority species' - these species have a reasonably high impact/or invasion potential.
For more details, please see Hayes et al. 2005.
The rankings determined in Hayes et al. 2005 will be used by the National Introduced Marine Pest Coordinating Group in Australia to assist in the development of national control plans which could include options for control, eradication and/or long term management.
Nyberg and Wallentinus (2005) state that C. fragile ssp. tomentosoides is one of five top risk species in Europe. The authors study quantitatively ranked species traits which facilitate introduction and predominance using interval arithmetic to search for common patterns among 113 marine macroalgae introduced in Europe. From the abstract Nyberg and Wallentinus (2005) “Three main categories were used: dispersal, establishment and ecological impact. These were further subdivided into more specific categories, a total of 13. Introduced species were compared with the same number of native species randomised from the same families as the introduced. Invasive species (i.e. species having a negative ecological or economical impact) were also compared with non-invasive introductions, separately for the three algal groups. In many categories, as well as when adding all species, the introduced species ranked more hazardous than the native species and the invasive species ranked higher than the non-invasive ones. The ranking within the three main categories differed, reflecting different strategies between the species within the three algal groups. When all categories (excluding salinity and temperature) were summed, the top five risk species, all invasive, were, in descending order, C. fragile ssp. tomentosoides, Caulerpa taxifolia, Undaria pinnatifida, Asparagopsis armata and Grateloupia doryphora, while Sargassum muticum ranked eight and Caulerpa racemosa ten. Fifteen of the twenty-six species listed as invasive were among the twenty highest ranked
Begin and Scheibling (2003) state that, "C. fragile ssp. tomentosoides can reproduce either sexually or parthenogenetically, releasing swarmers in the water column that are dispersed locally. It also reproduces vegetatively by fragmentation of the thallus, particularly in winter. New plants are established from fragments that are dispersed by currents and re-attach elsewhere, or from basal holdfasts that remain after fragmentation. Advective transport of fragments or entire plants may be particularly important in long-distance dispersal of this alga." Prince and Trowbridge (2004) claim that, "Sexual reproduction in the siphonaceous green seaweed C. fragile appears to be solely parthenogenetic in C. fragile ssp. tomentosoides (van Goor) Silva."
Reviewed by: Dr Jim Provan, Lecturer in Evolutionary Genetics School of Biology and Biochemistry, Queen’s University Belfast UK
Principal sources: Trowbridge, 1999. An assessment of the potential spread and options for control of the introduced green macroalga Codium fragile ssp.tomentosoides on Australian shores
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Tuesday, 8 November 2005