Pisidium henslowanum
Shepard, 1825
Common Name:
Henslow peaclam
Synonyms and Other Names:
henslow(’s) pea/pill clam, pisidiid clam
Identification:
Henslow’s pea clam has a thin, triangle- to oval-shaped, relatively long bivalve shell with evenly spaced coarse striae. The beaks are located posterior to the centre and the joint at the dorsal margin is relatively pointed. The height to length ratio is 0.8–0.9. The 2nd cardinal tooth inside the shell is V-shaped and larger than the 4th cardinal, which begins above the 2nd cardinal and lies obliquely. The 3rd cardinal is relatively thick and located at the posterior margin. In live specimens, there is only an anal siphon (Clarke 1981, Herrington 1962, Mackie 2000, Mackie et al. 1980, Pennak 1989).
Size:
reaches 4 to 4.6 mm in length (Clarke 1981, Herrington 1962, Holopainen 1979, Mackie 2000).
Native Range:
Pisidium henslowanum is a Holarctic species found in Eurasia, in countries such as Iceland, Scandinavia, France, Germany, Belgium, the territory of the former USSR, and the United Kingdom (Clarke 1981, Mackie 2000).
Great Lakes Nonindigenous Occurrences:
Pisidium henslowanum probably first appeared in the Great Lakes basin sometime prior to 1916, maybe even as early as the 1890s. It has been recorded from the Lake Ontario, Lake Michigan, and Lake Erie watersheds (Clarke 1981, Grigorovich et al. 2000, 2003, Heard 1961,1962, Herrington 1962, Johnson and Matheson 1968, Krieger 1984, Mackie 2000, Mackie et al. 1980, Ricciardi 2001, Wolfert and Hiltunen 1968).
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 Pisidium henslowanum are found here.
Full list of USGS occurrences
Table last updated 4/26/2024
† Populations may not be currently present.
* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).
Ecology:
In its native habitat P. henslowanum is most often found in rivers, canals, and streams of good water quality, while in North America it is mostly found in lakes and large rivers. Henslow’s pea clam can occur down to 20 m depth although it is more limited by lack of oxygen with increasing depth. It is typically associated with silt, mud, and sand assemblages. Densities in Europe have reached 330–9000 clams per m2 (Bishop and Hewitt 1976,Clarke 1981, Hinz et al. 1982, Holopainen 1979, Holopainen and Jonasson 1983, Holopainen and Ranta 1977, Jonasson 1984, Krieger 1984, Mackie et al. 1980, Smit et al. 1994,1995, Steiner and Turner 1998).
Even though European authors typically indicate that P. henslowanum requires relatively hard, calcium rich water, it can survive in somewhat softer water in the Connecticut River system. In this system the pH is 7.0–7.7 and the CaCO3 concentration is 25–35 mg/l (Smith 1986). Pisidium henslowanum reproduces hermaphroditically and may self-fertilize. The number of embryos per gravid adult ranges from 1–40 and generally increases with parental size. Young are released depending on temperature and oxygen availability. Pisidium henslowanum may produce one or two broods per year. The breeding season occurs in spring and summer. Young become mature at age 2 and the lifespan is thought to be 4–5 years (Clarke 1981, Holopainen 1979, Holopainen and Hanski 1986, Holopainen and Jonasson 1983, Mackie 2000, Smith 1986). Pisidium henslowanum, like many other pea clams, filters food from the water column directly above the substrate and from the sediments in which it lives, including bacteria, diatoms, detritus and other algae (Holopainen 1979, Mackie 2000).
Means of Introduction:
Pisidium henslowanum very likely arrived in ships to the Great Lakes basin. It was most likely delivered in solid ballast, which was in use at the turn of the century (Grigorovich et al. 2000, 2003).
Status:
Established where recorded.
Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...
Current research on the environmental impact of Pisidium henslowanum in the Great Lakes is inadequate to support proper assessment.
Potential:
Recent sampling in Lake Superior indicates that P. henslowanum has a greater abundance in the Duluth-Superior Harbor area than any species of native peaclam (Pisidium spp.), suggesting that P. henslowanum may possess some invasive trait(s) or compete with native species (Trebitz et al. 2010, Mackie 2000).
There is little or no evidence to support that Pisidium henslowanum has significant socio-economic impacts in the Great Lakes.
This species does not appear to have any impacts on human health or recreation.
There is little or no evidence to support that Pisidium henslowanum has significant beneficial effects in the Great Lakes.
This species does not appear to have any significant commercial or research value.
Management:
Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.
Note: Check federal, state/provincial, and local regulations for the most up-to-date information.
Control
Biological
There are no known biological control methods for this species.
Physical
There are no known physical control methods for this species.
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:
There has been some debate over whether or not P. henslowanum is native to North America. Those who believe it is a native species cite discoveries of occurrences in central and western Canada as well as shell deposits from 7000 years ago (Harris 1973), or mention that the population in the Holyoke Canals would have had difficulty spreading from the Great Lakes, considering that this canal system is not commercially navigable (Smith 1986). However, the general consensus amongst most authors is that P. henslowanum is an introduced species.
References
(click for full reference list)
Author:
Kipp, R.M., J. Larson, and A. Fusaro
Contributing Agencies:
Revision Date:
11/26/2019
Citation for this information:
Kipp, R.M., J. Larson, and A. Fusaro, 2024, Pisidium henslowanum Shepard, 1825: 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=130&Potential=N&Type=0&HUCNumber=DHuron, Revision Date: 11/26/2019, Access Date: 4/26/2024
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.