Lasmigona subviridis
Conrad, 1835
Common Name:
Green floater
Synonyms and Other Names:
Identification:
This freshwater bivalve exhibits a somewhat compressed to slightly inflated thin shell that is subrhomboid to subovate in shape. The periostracum is yellow, tan, dark green, or brown with dark green rays, and the nacre is white or light blue and sometimes pink near the beaks. The height to width ratio is greater than 0.48 and the beaks are low compared to the line of the hinge. There are two true lamellate pseudocardinal teeth and one relatively small interdental tooth in the left valve, as well as one long and thin lateral tooth in the right valve (Burch 1975, Peckarsky et al. 1993, Bogan 2002). Lasmigona subviridis can grow to 60–65 mm in length (Peckarsky et al. 1993, Bogan 2002).
Size:
up to 65 mm
Native Range:
Lasmigona subviridis was historically found throughout the Atlantic slope drainages in the Hudson, Susquehanna, Potomac, upper Savannah, Kanawha-New, and Cape Fear rivers. However, its range has retracted and it now occurs as disjunct populations in headwaters of coastal and inland rivers and streams of these drainages (Burch 1975, Mills et al. 1993, King et al. 1999, Clayton et al. 2001).
Great Lakes Nonindigenous Occurrences:
Lasmigona subviridis was recorded for the first time in the Lake Ontario drainage around 1959 in the Erie Barge Canal at Syracuse and in Chitenango Creek at Kirkville, New York. Around 1980 it was also found in the Finger Lakes area in New York State, part of the Lake Ontario drainage (Clark and Berg 1959, Johnson 1980, Mills et al. 1993)
Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Lasmigona subviridis are found here.
Full list of USGS occurrences
Table last updated 5/2/2024
† Populations may not be currently present.
Ecology:
Lasmigona subviridis usually occurs in streams, small rivers, and canals of low to medium gradient with slow pools and eddies, fine gravel and sand bottom, and mid-range calcium concentrations. It cannot tolerate either flooding or droughts. In general, freshwater mussels (unionids) are filter feeders and remove particulate organic matter from the water column (Bogan 2002, Harman 1970, Howard and Cuffey 2006, Strayer 1993).
Unionids typically require fish hosts for glochidial (larval) dispersal and transformation to the juvenile stage. The host species for L. subviridis is unknown, although evidence indicates that it may: a) rely on different fish species depending on different localities; or b) may not require a host fish, which is rare in North American unionids. Lasmigona subviridis is usually a simultaneous hermaphrodite and is bradytictic, or a long term brooder (Bogan 2002, King et al. 1999, Van der Schalie 1966).
Means of Introduction:
Lasmigona subviridis very likely dispersed into the Lake Ontario drainage from its native range or migrated via the Erie Canal but it could have been intentionally introduced.
Status:
Established where recorded.
Great Lakes Impacts:
There is little or no evidence to support that Lasmigona subviridis has significant environmental impacts in the Great Lakes.
There is little or no evidence to support that Lasmigona subviridis has significant socio-economic impacts in the Great Lakes.
There is little or no evidence to support that Lasmigona subviridis has significant beneficial effects in the Great Lakes.
Management:
Regulations (pertaining to the Great Lakes region)
NatureServe lists this species as ‘global vulnerable’ at moderate risk of extinction in its native range.
There are no regulations for this species as an invasive in the Great Lakes region.
Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Management research focuses primarily on preservation of populations within the native range.
Biological
Competition with dreissenid mussels will likely limit its expansion in the Great Lakes.
Chemical
A wide array of chemical molluscicides are available, but are not species-specific and may harm native species to a greater extent than non-natives.
Molluscicides are typically classified as either oxidizing or non-oxidizing compounds. Oxidizing chemicals include chlorine, chlorine dioxide, chloramines, ozone, bromine, hydrogen peroxide, and potassium permanganate. Non-oxidizing chemicals (including organic film-forming antifouling compounds, gill membrane toxins, and nonorganics) can be classified into several distinct groups: quanternary and polyquaternary ammonium compounds; aromatic hydrocarbons; endothall as the mono (N,N-dimethylalkyl amine) salt; metals and their salts (e.g., copper sulfate formulations); and niclosamide (including some formulations of Bayluscide). Bayluscide was initially developed as a sea lamprey larvicide, but has molluscicidal activity. While some of these products are biodegradable, many require detoxification or deactivation to meet state and Federal discharge requirements (USACE 2012).
Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.
Remarks:
Found in small to medium-sized streams with sand and gravel bottoms and low current. Spawns in August and releases glochidia the following June. Lasmigona subviridis is considered a species of concern, rare, imperiled, or critically imperiled in different parts of the United States. Populations in the Susquehanna and Potomac Rivers are genetically distinct from populations found further south due to reproductive isolation, and thus the two groups should be managed as two separate conservation units (Bogan 2002, Clayton et al. 2001, King et al. 1999, New York State Department of Environmental Conservation 2005).
References
(click for full reference list)
Author:
Kipp, R.M., A.J. Benson, J. Larson, and A. Fusaro
Contributing Agencies:
Revision Date:
11/6/2019
Citation for this information:
Kipp, R.M., A.J. Benson, J. Larson, and A. Fusaro, 2024, Lasmigona subviridis Conrad, 1835: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatLakes/FactSheet.aspx?Species_ID=146&Potential=N&Type=0&HUCNumber=DGreatLakes, Revision Date: 11/6/2019, Access Date: 5/2/2024
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.