Taxonomic name: Mytilopsis leucophaeata (Conrad, 1831)
Synonyms: Congeria cochleata , Congeria cochleatus , Mytilopsis cochleatus , Mytilopsis leucophaeta , Mytilopsis leucophaetus
Common names: brackish water mussel, Conrad's false mussel, dark false mussel
Organism type: mollusc
Mytilopsis leucophaeata is a bivalve mollusk native to the Gulf of Mexico and portions of the North American Atlantic coast that has invaded Europe and non-native locations of North America. It establishes dense populations that attach to natural and artificial surfaces and has become a problematic biofouler, especially to electrical and industrial plant cooling systems. Its ecological effects have yet to be determined.
Mytilopsis leucophaeata is a dreissenid, bivalve mussel that typically reaches 22 to 25 mm in length (Kennedy, 2010; Laine et al, 2006). It has a thick, rugrose periostractum covering its shell that is dark brown in adults and cream-colored in young specimens with fine to medium rough concentric lines. It commonly has “zebra stripes” and zig-zag patterns in juveniles (Verween et al, 2010; NOBANIS, 2011; Laine et al, 2006). Its shell shape is mytiliform and incurved with the anterior side depressed, hinge margin excavated, and teeth obsolete (Verween et al, 2010). The interior of the shell of M. leucophaeata is gray and has a shelf, or myophore, plate at the anterior with an apophysis, a small triangular tooth that serves as an attachment point for anterior retractor muscles, which is absent many similar-looking mussels including the Zebra mussel Dreissena polymorpha (Verween et al, 2010; Zebra Mussel Information System, 2002). It is an epifaunal species that attaches to hard substrates with byssal threads (NOBANIS, 2011; Verween et al, 2010).
Dreissena polymorpha, Dreissena rostriformis (bugensis)
coastland, estuarine habitats, marine habitats, riparian zones, wetlands
Mytilopsis leucophaeata generally inhabits oligohaline to mesohaline estuarine environments (Kennedy, 2010). It is strongly euryhaline and has been recorded from salinities of 0-25 PSU with an optimal range of 0.75-20.9 PSU (Verween et al, 2010). It is also fairly temperature tolerant and may tolerate temperatures from 6.8°C to 37°C, but its optimum range, in which reproduction occurs, is between 15°C to 27°C (Verween et al, 2010; Rajagopal et al, 2005b; NOBANIS, 2011). It attaches to artificial and natural substrates including stones, woody debris, oysters, conduits, bottles, stone walls, wooden posts and other structures (Verween et al, 2010; Kennedy, 2010).
Mytilopsis leucophaeata is a biofouling species which commonly disturbs coolant water systems of industrial and power plants. Its rapid reproduction in such an ideal environment may result in extremely dense populations that clog water intakes and may damage or cause failure to systems (Rajagopal et al, 2002c; Kennedy, 2010; Verween et al, 2006). Specific examples of its biofouling have been reported from Belgium, Finland, and the Netherlands with densities ranging from tens of thousands to even millions of individuals/m2 (Verween et al, 2007a; Laine et al, 2006; Rajagopal et al, 2002b). M. leucophaeata also fouls boats, ropes, cages, and other marine equipment (Bergstrom, 2004). Aside from biofouling, dense populations M. leucophaeata alter ecosystems and likely have significant ecological effects similar to that of the more widely researched dreissenid Zebra mussel, (Dreissena polymorpha), which demand further investigation.
Native range: Mytilopsis leucophaeata is native to the Gulf of Mexico and part of North Americas Atlantic coast. Its native range on the Atlantic coast is debated (Kennedy, 2010; NOBANIS, 2011).
Known introduced range: North America and Europe including Belgium, Finland, France, Netherlands, Spain, Ukraine, and Wales.
Local dispersal methods
Boat: Local dispersal could involve fouling on boats or transport in live wells or bilge systems (Therriault, T., pers. comm., 2005).
Transportation of habitat material (local): Local dispersal could involve diffusion, especially transport during larval stages as veligers (Therriault, T., pers. comm., 2005).
Preventative measures: Early detection and prevention of establishment of Mytilopsis leucophaeata is essential, especially in industrial plant cooling systems (Verween et al, 2002). Adherence to GloBallast (GEF/UNDP/IMO Global Ballast Water Programme) ballast water standards may prevent is establishment in new locations.
Physical: The use of a submersible cleaning and maintenance platform (SCAMP) was found ineffective at removing Mytilopsis leucophaeata (Davidson et al, 2008).
Chemical: Chlorination is effective in controlling Mytilopsis polymorpha in water cooling system intakes, which has been applied successfully to the similar biofouler Driessena polymorpha (Rajagopal et al, 2002a; Verween et al, 2009a). M. leucophaeata is more resistant to chlorination than D. polymorpha and has been found to close its valves when exposed to chlorine. Therefore, continuous levels of chlorination are necessary to achieve results (Rajagopal et al, 2003). Levels of 0.25 mg/L residual chlorine achieved 100% mortality in a little over 100 days (Rajagopal et al, 2002b). Higher levels of 1mg/L achieved 100% mortality after 588 hours (Rajagopal et al, 2003). Such durations of continuous chlorination may not be practical though (Rajagopal et al, 2002a). Chlorine levels of 0.6mg/L were effective against M. leucophaeata embryos even at short intervals (Verween et al, 2009a). Experimentation with pulse chlorination has been recommended but not evaluated (Rajagopal et al, 2002a). Peracetic acid, used as commercial product Degaclean, was also found to be effective against embryos achieving over 98% mortality at 3 mg/L in a 15 minute exposure. Although it may be a more ecologically friendly alternative to chlorine, its higher cost may be prohibitive (Verween et al, 2009a).
Mytilopsis leucophaeata is a filter feeder that consumes phytoplankton, plant detritus, diatoms, and other organic matter (Verween et al, 2010; Kennedy, 2010).
Mytilopsis leucophaeata is a dioecious species that reproduces sexually by external fertilization (Zebra Mussel Information System, 2002). Reproduction may occur continuously in some locations or from the late spring to early fall in others (Verween et al, 2009b; Kennedy, 2010; NOBANIS, 2011). The minimum reported temperature required for spawning is about 13-15°C (NOBANIS, 2011; Verween et al, 2010).
The larvae of Mytilopsis leucophaeata are planktonic and have been found to metamorphose in about 6 days to 2 weeks depending on temperature (Sidall, 1980). It has been found to have an average growth rate of about 3-6 mm/year (Verween, 2006). Young Dark false mussels in Amsterdam Harbor were measured to an average of 4 mm by the end of May after a period of no growth over winter. Their subsequent average sizes included 8 mm(end of June), 11 mm (end of July), 15 mm (end of August), 17 mm (mid-September), and 19 mm (end of October). The maximum size was about 23–24 mm and no individual seemed to be older than a year and a few months (Vorstman, 1933). However, these sizes may not be typical as first year and even maximum sizes of 10-15 mm have also been reported (Kennedy, 2010).
Reviewed by: Therriault, T.W Department of Fisheries and Oceans. Pacific Biological Station Canada
Principal sources: Therriault et al. 2004. Molecular resolution of the family Dreissenidae (Mollusca: Bivalvia) with emphasis on Ponto-Caspian species, including first report of Mytilopsis leucophaeata in the Black Sea basin
Rajagopal et al. 2002b. How effective is intermittent chlorination to control adult mussel fouling in cooling water systems?
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Wednesday, 23 February 2011