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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Charru mussel

Synonyms and Other Names: M. falcata, M. strigata, M. arciformis

Identification: The shell is elongate, oval in shape, smooth with semicircular growth lines some zigzag in pattern, and varies in color from dark greenish brown to black (Keen 1971, Mediodia et al. 2017). The interior of the shell is iridescent white with a broad band of purple along the posterior margin and a dark orange foot (Mediodia et al. 2017). This species is similar in shape to common native mussels (Geukensia demissa and Brachiodontes spp.) but can be distinguished by the lack of distinct radial ridges or ribs on the exterior of the shell (TNC 2006).

Size: In the native range 4.4 cm long and 2.2 cm wide. Maximum sizes reported in invaded population are 4.87 cm in St. Mary’s, Georgia (Stenyakina et al. 2009) and 5.65 cm in the Philippines (Mediodia et al. 2017).

Native Range: Native to coastal regions of Central and South America, ranging on the Pacific coast from Guaymas, Gulf of California, Mexico south to Ecuador, Panama, and the Galapagos Islands, and along the Atlantic coast from Venezuela to Argentina (Keen 1971, Calazans et al. 2017).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Charru mussels occur in mud flats and shallow lagoons (Keen 1971). This species possesses broad environmental tolerances surviving in salinities from 2 to 31ppt (Yuan et al. 2010) and mean temperature tolerances from 9 to 31 °C (Brodsky et al. 2011). In the native range, Charru mussels spawn from July to October, but in the invaded range spawning can extend throughout the year (Stenyakina et al. 2009). Reproductive maturity is reached with a minimum shell size of 1.25 cm (Stenyakina et al. 2009). Charru mussels have external fertilization with a pelagic larval stage (Stenyakina et al. 2009). Adult mussels have strong byssal threads that aid in the attachment to hard substrates (Mediodia et al. 2017).

Means of Introduction: Probable ballast water introduction (Carlton 1992).

Status: Unknown

Impact of Introduction: This colonizing species created a biofouling problem at the Jacksonville Electric Authority's Northside Generating Station by clogging an intake pipe filter feet away from steam condensers. The mussels in Mosquito Lagoon were collected off a reef where they could compete with native organisms for food and habitat.
Yuan et al. (2016) found that native oyster spat survival and growth were reduced in the presence of Charru mussel.

Remarks: Under starvation conditions in a laboratory experiment, Stenyakina et al. (2009) found food availability played a significant role in sex ratios causing mussels to change from female to male. This could provide the mussel with the advantage to conserve energy under stressful environmental conditions.

References: (click for full references)

Boudreaux, M.L., and L.J. Walters. 2006. Mytella charruana (Bivalvia: Mytilidae) a new, invasive bivalve in Mosquito Lagoon, Florida. Nautilus 120:34-36.

Brodsky, S., L. Walters, K Schneider, and E. Hoffman. 2011. Cold temperature effects on byssal thread production by the native mussel Geukensia demissa versus the non-native mussel Mytella charruana. University of Central Florida Undergraduate Research Journal 5:15-24.

Calazans, S.H., L.J. Walters, F.C. Fernandes, C.E.L. Ferreira, and E.A. Hoffman. 2017. Genetic structure provides insights into the geographic origins and temporal change in the invasive charru mussel (Sururu) in the southeastern United States. PloS ONE 12:e0180619.

Carlton, J.T. 1992. Introduced marine and estuarine mollusks of North America: and end-of-the-20th-century perspective. Journal of Shellfish Research 11:489-505.

Keen, A.M. 1971. Sea shells of tropical west America. Second edition. Stanford University Press, California, 1064 p.

Lee, H.G.1987. Immigrant mussel settles in northside generator. The Shell-O-Gram 28:7-9.

Mediodia, D.P., S.M.S. De Leon, N.C. Anasco, and C.C. Baylon. 2017. Shell morphology and anatomy of the Philippine Charru mussel Mytella charruana (d’Orbigny 1842). Asian Fisheries Society 30:185-194.

Kingsley-Smith, P. 2016. South Carolina Department Natural Resources, Marine Resources Research Institute state report. Charleston, SC. Pages 1-5.

Stenyakina, A., L.J. Walters, E.A. Hoffman, and C. Calestani. 2010. Food availability and sex reversal in Mytella charruana, an introduced bivalve in the southeastern United States. Molecular Reproduction and Development 77:222-230.

The Nature Conservancy (TNC). 2006. Invasive mussel alert: Mytella charruana found in Florida waters.

Yuan W, L.J. Walters, K.R. Schneider, and E.A. Hoffman. 2010. Exploring the survival threshold: A study of salinity tolerance of the nonnative mussel Mytella charruana. Journal of Shellfish Research. 29:415–422.

Yuan, W.S., E.A. Hoffman, and L.J. Walters. 2016. Effects of nonnative invertebrates on two life stages of the native eastern oyster Crassostrea virginica. Biological Invasions 18:689-701.

Other Resources:

Immigrant Mussel Settles In Northside Generator

Author: M.E. Brown and A.J. Benson

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.