Invasive Species Marine Algae

Wakame (Asian kelp, Japanese kelp) - Undaria pinnatifida


Description and Identification

Wakame is a large brown seaweed found from the low tide level down to 15 m, often on man-made structures such as marina pontoons, plastic and boat hulls.  In soft sediments, this algae attaches to hard surfaces such as oyster shell. Wakame is most commonly found between 1-3 m. It is a type of kelp with a branched holdfast 9the structure that fixes the algae to a surface, as a root fixes a plant in soil) and a stipe (joins the fronds to the holdfast, like a stalk) with wavy edges, giving it a corrugated appearance. The fronds are broad, flattened and lanceolate or spear shaped, with a midrib. The edges of the fronds are also wavy. The algae can reach an overall length of 1 to 3 m.
 (Wakame - image Keith Hiscock www.marlin.ac.uk)

 Spear-shaped frond with strong mid-rib (Salcott Channel)

 

 

 

 Branched holdfast, wavy stipe (Salcott Channel)

 

Key features:
    Dark brown colour
    Usually 1.5-2 m long
    Branched holdfast
    Stipe wavy or corrugated above holdfast
    Frond spear-shaped, broad and indented with a strong midrib

Problems caused
Wakame is an opportunistic species, able to grow quickly, establish on disturbed and artificial substrates and to tolerate a wide range of environmental conditions, such as light, exposure, temperature and salinity.  It grows in dense stands, forming thick canopies. These ‘forests’ may result in lack of light and space for native species, as well as creating changes in the water flow. As with all introduced species, Wakame is likely to change the structure and interactions of the ecosystem. This kelp can also foul ropes, harbour structures and boat hulls and may block water intake systems. Large banks of drifting algae may build up on beaches, forming unpleasant smelling piles, adversely affecting tourism.

Distribution
Wakame is native to the Northwest Pacific, mainly Japan, China and Korea, where it is grown commercially for food. It was introduced to France with commercial oysters and spread to the UK on the hulls of leisure boats to marinas in southern England.   It was first recorded in the Solent (the sea separating the Isle of Wight from mainland Britain) in 1994 and in Ramsgate, Kent in 2003. It has also been recorded in Devon and the Channel Islands, and in France and the Netherlands. The species appears to be spreading northwards, as a sample was collected from the Salcott Channel, part of the River Blackwater in Essex by Essex Wildlife Trust in 2006.

Control measures
The approach to Wakame management has been to slow its spread and so reduce the chances of it reaching new locations. Eradication of this species is unlikely since it is a highly opportunistic and adaptable species. Wakame is dispersed naturally during a microscopic phase of life and by human vectors, such as attachment to boat hulls. Management of these vectors and raising awareness of this invasive species should help to slow its spread. In the long-term, it is hoped that it may be possible to treat boat hulls with UV light or high-pressure and use heated water to kill spores efficiently.

Actions that the public can take
a) Inform Essex Biodiversity Project if this species is found, for example growing on oyster shells or on boat hulls.
b) Explain to others why this, and other invasive species, cause problems for native species (problems caused) and encourage them to report sightings.

Sources of information and References
    Marine Life Information Network for Britain and Ireland  http://www.marlin.ac.uk/species/Undariapinnatifida.htm
    Global Invasive Species Database http://www.issg.org/database/species/ecology.asp?fr=1&si=68&sts=
    ICES: Alien Species Alert http://www.ices.dk/reports/ACME/2006/WGITMO06.pdf
    FAO Fisheries Global Information System (FIGIS): http://www.fao.org/fi/website/FIRetrieveAction.do?dom=species&fid=2777
    AlgaeBase http://www.algaebase.org/search/species/detail/?species_id=350
    Joint Nature Conservation Committee non-native species http://www.jncc.gov.uk/page-1676

Pacific Wireweed  - Sargassum muticum


Description and Identification
Sargassum is an olive-brown seaweed with long fronds and characteristically forms floating mats on the sea surface during the summer. The fronds are often more than 1 m long and the whole seaweed can grow up to 16 m in length. The stem has alternating branches with flattened oval blades and small round gas bladders.
Wireweed - Image Keith Hiscock www.marlin.ac.uk

Key features:
    Fronds often more than 1 m in length.
    Olive-brown colour.
    Regular alternating branches along stem.
    Flattened oval blades and round gas bladders along branches.

Problems caused
Wireweed grows on hard substrata in shallow waters and grows upwards to form large floating masses. These masses create several problems to native species including reduced light availability, changes and slowing down of water flow, increased sedimentation and reduced nutrients available to native species. Wireweed can out-compete native species because it grows so fast (up to 10 cm a day), reproduces during the first year of growth and can fertilise itself. It grows in a variety of habitats because it is tolerant of environmental fluctuations, for example salinity and temperature, and so may be found in estuaries. In addition, this species causes economic problems when the floating mats foul on boat propellors, block intake pipes, foul fishing nets and cause loss of amenity in tourist areas by impacting water sports such as swimming, surf boarding and dinghy sailing. In late summer, large mats may build up on the shore, forming dense, slowly rotting clumps. Native species possibly adversely affected by Wireweed include eelgrass Zostera marina, Sugar kelp Laminaria saccharina and Sea oak Halidrys siliquosa.

Distribution
Wireweed is native to the waters around Japan. It was introduced with commercial oysters to France and subsequently spread to Britain. Although first recorded in the Isle of Wight in 1971, wireweed probably first appeared in the English Channel in the late 1960s. Wireweed has now spread along the south coast of England and along the north Cornwall coast to Lundy; it has been recorded in Northern Ireland and Scotland and south of the Thames at several locations in Kent. It has been found on the North Sea coast in Essex (Salcott Channel, River Blackwater, 2006), Suffolk and Norfolk. The alga spreads by natural means in ballast water, on boat hulls and by floating plants or fragments.

Control measures
Wireweed in now widespread and it is believed that the spread of this species throughout UK waters is inevitable. Various methods of control have been tested: physical removal by hand; several types of herbicide; biological control using herbivores; and trawling, cutting and suction have also been tried. Physical removal is labour intensive, time-consuming and needs to be on-going; the herbicides failed due to lack of selectivity and the large doses needed, biological control failed because, although the species tested would feed on wireweed, they preferred other species. Cutting and suction appears to be the most effective method of controlling wireweed. However, whichever method is used the alga always quickly regrows and effective methods for its permanent removal have not been found.

Essex Biodiversity Project aims to increase public awareness of the problems caused by this species. EBP will not be taking direct action to control the species.

Actions that the public can take
a) Inform Essex Biodiversity Project if this species is found, for example in floating mats at sea or on the beach.
b) Explain to others why this, and other invasive species, cause problems for native species (problems caused) and encourage them to report sightings.

Sources of information and References
    Marine Life Information Network for Britain and Ireland  http://www.marlin.ac.uk/species/Sargassummuticum.htm
    Global Invasive Species Database  http://www.issg.org/database/species/ecology.asp?si=727&fr=1&sts=
    Joint Nature Conservation Committee non-native species  http://www.jncc.gov.uk/default.aspx?page=1677
    AlgaeBase http://www.algaebase.org/search/species/detail/?species_id=90&-session=abv4:0A740E210cd1b19460TJj290A5B7