Introduction to Mussels (Mytilidae) and False Mussels (Dreissenidae)
Both these bivalve families contain invasive species.
True mussels: (family Mytilidae) The mussel Mytilus galloprovincialis (Lamarck, 1819) has not been found in Nordic waters, but this originally Mediterranean species is invasive in the USA, South Africa, and NE Asia. There is a possibility that M. trossulus, which has been identified as a separate species in the Baltic Sea is also an invasive or at least cryptogenic species. However, not all specialists agree that it is a separate species, and "pure" M. trossulus strains have not been found in the Baltic Sea. All seem to be "infected" with M. edulis alleles (Riginos & Cunningham, 2005). The identity and origin of M. trossulus is too complicated to be included in the present project. Some pertinent references are given below.
False mussels: (family Dreissenidae) False mussels belong to the family Dreissenidae, which contains some of the worst invasive species, e.g. the zebra mussel, Dreissena polymorpha (Palas, 1771) and the quagga mussel, Dreissena bugensis Andrusov, 1897. These species occur predominantly in freshwater or brackish water of very low salinity. Mytilopsis leucophaeata occurs at somewhat higher salinity, but not in full strength seawater. Another species M. sallei (Recluz, 1849) from the Caribbean is invasive in tropical waters of Asia and Australia.
False mussels are most easily separated from true mussels by the presence of a calcareous plate interiorly at the hinge line. This shelf-like plate has different size and shape in different species.
Picture of Dreissena polymorpha shell interior with septum. Photo by Kathe Rose Jensen.
Mytilus edulisshell interior without septum. Photo by Kathe Rose Jensen.
More information on false mussels included in this key:
Beaumont, A.R., Hawkins, M.P., Doig, F.L., Davies, I.M. and Snow, M. 2008. Three species of Mytilus and their hybrids identified in a Scottish Loch: natives, relicts and invaders? Journal of Experimental Marine Biology and Ecology 367: 100-110.
Johannesson, K., Kautsky, N. and Tedengren, M. 1990. Genotypic and phenotypic differences between Baltic and North Sea populations of Mytilus edulis evaluated through reciprocal transplantations. II. Genetic variation. Marine Ecology Progress Series 59: 211-219.
Kautsky, N., Johannesson, K. and Tedengren, M. 1990. Genotypic and phenotypic differences between Baltic and North Sea populations of Mytilus edulis evaluated through reciprocal transplantations. I. Growth and morphology. Marine Ecology Progress Series 59: 203-210.
Kijewski, T.K., Zbawicka, M., Väinölä, R. and Wenne, R. 2006. Introgression and mitochondrial DNA heteroplasmy in the Baltic populations of mussels Mytilus trossulus and M. edulis. Marine Biology 149: 1371-1385.
Pedersen, E.M., Hunt, H.L. and Scheibling, R.E. 2000. Temporal genetic heterogeneity within a developing mussel (Mytilus trossulus and M. edulis) assemblage. Journal of the Marine Biological Association of the U.K. 80: 843-854.
Ridgway, G. and Nævdal, G. 2004. Genotypes of Mytilus from waters of different salinity around Bergen, Norway. Helgoland Marine Research 58: 104-109.
Riginos, C. and Cunningham, C.W. 2005. Local adaptation and species segregation in two mussel (Mytilus edulis x M. trossulus) hybrid zones. Molecular Ecology 14: 381-400.
Saavedra, C., Stewart, D.T., Stanwood, R.R. and Zouros, E. 1996. Species-specific segregation of gender-associated mitochondrial DNA types in an area where two mussel species (Mytilus edulis and M. trossulus) hybridize. Genetics 143: 1359-1367.
Tedengren, M., André, C., Johannesson, K. and Kautsky, N. 1990. Genotypic and phenotypic differences between Baltic and North Sea populations of Mytilus edulis evaluated through reciprocal transplantations. Marine Ecology Progress Series 59: 221-227.