Geukensia demissa (mollusc)

Ecology Distribution Management Info Impact Info References and Links Contacts

Taxonomic name: Geukensia demissa (Dillwyn, 1817) Synonyms: Arcuatula demissa (Dillwyn, 1817), Ischadium demissa (Dillwyn, 1817), Modiola plicatulus (Lamarck, 1819), Modiola semicostata (Conrad, 1837), Modiolus plicatulus, Mytilus demissa (Dillwyn, 1817) Common names: Atlantic ribbed marsh mussel, ribbed horsemussel, ribbed mussel (English) Organism type: mollusc Geukensia demissa (ribbed mussel) is native to the east coast of North America and have been introduced to California, Mexico, Texas and Venezuela. Geukensia demissa are reported to cause problems for the California Clapper Rail (Rallus longirostris obsoletus), with whom they share the same habitat, by the trapping and drowning of birds in marshes caused by their shells sticking out of the mud. Description Geukensia demissa grows to be an average of 10cm in length, with the maximum size being 13cm. The umbo or hump is located at the center of the growth lines which is close to the head end of the shell. The thin, glossy tissue that covers the shell is called the periostracum. It is usually olive-brown, yellowish-brown, dark brown or black. The grayish-white part of the shell is usually seen where the periostracum has been worn away. The interior of G. demissa is "silvery white or bluish white, often iridescent, with purple tints toward the hind margin" (Cohen, 2005). Geukensia demissa settles slightly in the mud with the head end pointed downward and the large, round hind sticking out of the mud (Cohen, 2005). Similar Species Brachidontes exustus, Septifer bifurcatus More Occurs in: estuarine habitats, marine habitats Habitat description Geukensia demissa is found on the Atlantic coast of North America in intertidal zones and marshes (Cohen, 2005). It is often found living on the cordgrass Spartina foliosa. This species is abundant at the lowest shore levels of a marsh (Franz, 1997). G. demissa is most abundant in estuarine lakes and brackish waters in Venezula (Báez et al. 2005). The highest water temperature tolerated is 56°C and salinities twice as salty as the ocean (Cohen, 2005). At low tide, G. demissa closes its shell to conserve water (Coen and Walters, undated). General impacts Torchin et al. (2005) report on the report on the distribution, abundance, and biomass of the introduced ribbed mussel, G. demissa, at the Estero de Punta Banda (EPB), on the Pacific Coast of Baja California Norte, Mexico. The authors report it is unlikely that G. demissa competes with native bivalves for space as they occupy different habitats, however, G. demissa could be competeing with native bivalves and suspension feeders for food as thay are capable of filtering large amounts of water. A significant impact of G. demissa was its affect on vegetation. The association between the native cordgrass (S. foliosa) and the introduced mussel was positive, increased mussel presence due to increased reproduction resulted in increased cordgrass prodcution. Increased cordgrass meant a decrease in the habitat of other benthic muddwelling invertebrates, and many of the birds that tend to forage on tidal flats (Torchin et al. 2005). The introduced mussel has an impact on the endangered California clapper rail (see Rallus longirostris obsoletus in IUCN Red List of Threatened Species) with which it shares a common habitat. The posterior margin of the shell which protrudes above the surface of the mud can clamp on to the toes and beaks of small birds causing toe losses and sometimes death. Uses Geukensia demissa is a bioindicator of pollution and water quality for pollution assessment studies. This species is a filter feeder which makes it a good specimen for sediment evaluation (Coen and Walters, undated). G. demissa improves water quality by cycling nutrients in estuarine habitats (Coen and Walters, undated). At the time of the summer tidal cycle, G. demissa can filter a volume of water that exceeds the total marsh volume (Jordan and Valiela, 1982). In Georgia, biodeposition from G. demissa is a large part of the annual marsh sediment budget which is important geologically to marshes (Smith and Frey, 1985). Notes On the northwest Atlantic coast this species is known as Geukensia demissa and on the northeast Pacific coast it is known as Ischadium demissum (Cohen and Carlton, 1995). Geographical range Native range: Quebec, Nova Scotia, Massachusetts, New York, Delaware, North Carolina, Connecticut, New Jersey, Florida (USA), Georgia (USA), South Carolina (WAMD, 2005; Coen and Walters, undated; Smith and Frey, 1985; Brousseau, 1984; FONS, 1998; eNature, 2005) Known introduced range: Texas, California, Mexico, Venezuela (Báez et al. 2005; eNature, 2005; Torchin et al. 2005; NAS, 2005) Introduction pathways to new locations Live food trade: Carlton (1992) suggests that local dispersal pathways within the wetlands in California were most likely to be with movements of shellfish and due to ballast water introductions. Ship ballast water: G. demissa was probably introduced into the Lake Maracaibo system, accidentally on a ships hull or in ballast water or on the legs of migratory birds (Báez et al. 2005). Ship/boat hull fouling: G. demissa was probably introduced into the Lake Maracaibo system, accidentally on a ships hull or in ballast water or on the legs of migratory birds (Báez et al. 2005). Management information We have been unable to locate any management information for this particular species. Nutrition Geukensia demissa is a filter feeder that eats plankton and organic particles (Cohen, 2005) during high tide (Coen and Walters, undated). G. demissa feeds on bacterioplankton and is known as one of the few to do so. Feeding only occurs when the mussel is fully submerged (Coen and Walters, undated). During high tide though, aerial exposure reduces the filter feeding time of G. demissa (Borrero, 1987) Reproduction Geukensia demissa releases sperm and eggs into the water where they can be fertilized. The larvae is in the water from the beginning of summer to the beginning of fall (Cohen, 2005). Báez et al (2005) discussed how G. demissa spawns more often in warmer temperatures. There are two distinct spawning peaks in the tropics: July and December. These are the rainy season and the dry season respectively. Six stages represent the production of gametes in G. demissa. During the resting stage the sex of G. demissa is uncertain and no follicles are present. Packed connective tissue hinders the ability to view the genitals. During the early development stage the first signs of gametogenesis is present. In the late stage sperm can be observed. The morphologically mature stage shows sperm moving to the lumen and at this point females ova have reached maximum size. The spawned stage is when a great number of visible ova are present in the females follicles and "dense bands of mature sperms are visible" in the male. During the post spawn stage the follicles that held the sperm and the ova collapse and degenerate (Báez et al. 2005). Lifecycle stages Geukensia demissa can live to be over 15 years (Cohen, 2005). Growth is enhanced by increasing Nitrogen levels (Evgendou and Valiela, 2002). Principal sources: Cohen, Andrew N. 2005 Guide to the Exotic Species of San Francisco Bay. Geukensia demissa San Francisco Estuary Institute, Oakland, CA, Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG) To contribute information, please contact Shyama Pagad. Last Modified: Friday, 25 May 2007