Invasion History

First Non-native North American Tidal Record: 1869
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1869

General Invasion History:

Ischadium recurvum was first described by Rafinesque (as Mytilus recurvus) in 1820, from the Mississippi River near New Orleans (Johnson 1915). In 1822 Say gave it (as Mytilus hamatus) a similar distribution: 'Inhabits the Gulf of Mexico, frequently carried to New Orleans attached to the common oyster' (Say 1858). The Hooked Mussel is native to Chesapeake Bay, based on its occurrence in Tertiary fossils (Conrad 1830), museum specimens (Academy of Natural Sciences of Philadelphia 2011; US National Museum of Natural history collections) and archaeological excavations (Torben Rick, personal communications). It is also likely native to Delaware Bay (Maurer et al. 1974), but its range was extended northward to New England by 19th century oyster transplants (Smith and Prime 1870; Perkins 1871; Richards 1938; US National Museum of Natural History 2011). Most of these introduced mussels have apparently died out, but populations persisted or have been re-introduced in Rhode Island estuaries (Sheldon Pratt, personal communication). There are two puzzling old records of individuals of this species in southern California (Carlton 1979).

North American Invasion History:

Invasion History on the West Coast:

The only two records from California are both puzzling. Dall (1921, cited by Carlton 1979) reported it from the 'Newport area', California. The specimens were dredged from the Pacific Ocean off Newport (Calton 1979). Live specimens of this species were also dredged off Redondo Beach in Santa Monica Bay, in 1931, at 152 m depth (Carlton 1979). Neither collection was associated with oysters, and both were in an exceptional habitat for this estuarine species. These have to be attributed to ballast water or fouling, but they occurred some distance from the nearest major ports, Los Angeles-Long Beach Harbors.

Invasion History on the East Coast:

Although early records are somewhat sporadic, the northern range edge of I. recurvum appears to be Chesapeake or Delaware Bay (Dall 1889; Maurer et al. 1974; US National Museum of Natural History collections, Academy of Natural Sciences of Philadelphia 2011). From 1869 to 1938, there were numerous reports of I. recurvum from Barnegat Bay, New Jersey to Welfleet Massachusetts, on Cape Cod Bay, usually on newly transplanted oysters (Smith and Prime 1870; Johnson 1915; Richards 1938; Academy of Natural Sciences of Philadelphia 2011; US National Museum of Natural History 2011). There have been few recent records north of the Chesapeake, and suggestions that the introduced mussels have died out due to cold winter weather (Gosner 1971; Morris 1975). However, they are locally common in brackish tributaries (Pettaquamscutt River, Kickamuit River) of Narragansett Bay, Rhode Island (Sheldon Pratt 1997, personal communication). Ischadium recurvum has been collected in fouling on ships on the East Coast of the United States (Visscher 1927; Davidson et al. 2008). The established populations in Rhode Island could result from persistence from the early oyster introductions, or represent new introductions by pleasure boats (James Carlton, personal communication).

Invasion History Elsewhere in the World:

Elsewhere in the World- In October 2018, specimens of the Hooked Mussel were found in the Nordseekanaal, in the Coenhaven section of Amsterdam. Growth lines indicated that the largest mussels were 6-7 years old, and that a population was established (Goud et al. 2019)


Ischadium recurvum is roughly triangular in shape, and strongly curved toward the beak, with strong radiating ribs. The beak is terminal, and the hinge has 3 or 4 small teeth. The exterior color of the shell is gray or brown, to dull bluish-black. The interior is polished and purplish, with a whitish margin. Adult mussels are 25-50 mm in length. This species is characteristic of estuaries, and is usually found attached to oysters, logs, pilings, or rocks, often in brackish water (Abbott 1974; Gosner 1971; Morris 1975; Lippson and Lippson 1997).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Pteriomorphia
Order:   Mytiloida
Family:   Mytilidae
Genus:   Ischadium
Species:   recurvum


Brachidontes recurvus (Rafinesque, 1820)
Mytilus hamatus (Say, 1822)

Potentially Misidentified Species

Brachidontes exustus



Ischadium recurvum has separate sexes. Animals mature at about one year of age. Eggs are brooded, but sperm are released into the water column. Fertilized eggs are brooded and develop into planktotrophic shelled veligers (Allen 1960).

Larvae settle on a variety of hard substrates, including oysters, wood, and rocks (Abbott 1974; Gosner 1971; Morris 1975; Lippson and Lippson 1997). They tolerate an extremely wide range of temperature and salinity, with water temperatures of 0 to 35?C (Nauman and Cory 1969) and salinities of 4.5-36 PSU (Allen 1960; Castagna and Chanley 1973). However, based on their geographical distribution and patterns of abundance, they appear to be most successful in regions with mild winters and low salinities (Abbott 1974; Morris 1975; Lippson and Lippson 1997).



Trophic Status:

Suspension Feeder



General HabitatCoarse Woody DebrisNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatVessel HullNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Minimum Temperature (ºC)0Based on geographical range
Maximum Temperature (ºC)37Powerplant effluent, Patuxent River MD (Nauman and Cory 1969)
Minimum Salinity (‰)4.5Experimental (Allen 1960)
Maximum Salinity (‰)36Gulf of Mexico salinity
Minimum Reproductive Temperature11.6Field (Allen 1962, Chesapeake Bay)
Maximum Reproductive Temperature24.5Field (Allen 1962, Chesapeake Bay)
Minimum Reproductive Salinity8Experimental (Allen 1960)
Maximum Reproductive Salinity36Gulf of Mexico salinity
Minimum Length (mm)25Size at early maturity (Abbott 1974; Morris 1975; Gosner 1978)
Maximum Length (mm)50Abbott 1974; Morris 1975; Gosner 1978
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

In its native range, Ischadium recurvum is often an abundant fouling organism and may 'wrap up' oysters when abundant (Andrews 1953), causing the oysters to grow in a misshapen fashion (Allen 1962). Ischadium recurvum may compete with oyster spat for space (Andrews 1953). Competition for food with oysters and other suspension-feeding fouling organisms is possible, especially when large biomasses of I. recurvum are present.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1820 Native Estab
CAR-II None 0 Native Estab
CAR-III None 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 1871 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 1869 Def Estab
NA-ET2 Bay of Fundy to Cape Cod 1879 Def Failed
NEP-VI Pt. Conception to Southern Baja California 1921 Def Failed
M090 Delaware Bay 1889 Native Estab
M130 Chesapeake Bay 1883 Native Estab
M020 Narragansett Bay 1889 Def Estab
M040 Long Island Sound 1869 Def Unk
M060 Hudson River/Raritan Bay 1870 Def Unk
M128 _CDA_M128 (Eastern Lower Delmarva) 0 Native Estab
M120 Chincoteague Bay 1916 Native Estab
N180 Cape Cod Bay 1879 Def Failed
P040 Newport Bay 1921 Def Failed
P060 Santa Monica Bay 1931 Def Failed
M070 Barnegat Bay 1894 Def Unk
NEA-II None 2012 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Abbe, George R. (1987) Epifauna, In: Heck, Kenneth L.(Eds.) Ecological studies in the middle reach of Chesapeake Bay- Calvert Cliffs. , Berlin. Pp. 82-91

Abbott, R. Tucker (1974) Amarican Seashells, Van Nostrand Reinhold, New York. Pp. <missing location>

Academy of Natural Sciences of Philadelphia 2002-2016a Malacology Collection Search.

Allen, J. Frances (1960) Effect of low salinity on survival of the curved mussel, Brachidontes recurvus, Nautilus 74(1): 1-8

Allen, J. Frances (1962) Gonad development and spawning of Brachidontes recurvus in Chesapeake Bay, Nautilus 75: 149-156

Andrews, J. D. (1953) <missing title>, Chesapeake Bay Institute, Johns Hopkins University, Baltimore, Maryland. Pp. <missing location>

Boito, Lucilla; Van den Neucker, Tom; Van Damme, Stefan; Schoelynck, Jonas (2923) First record of the alien hooked mussel Ischadium recurvum (Rafinesque, 1820) (Bivalvia: Mytilidae) in Belgium, Belgian Journal of Zoology 152: 157–162

Calder, Dale R.; Brehmer, Morris L. (1967) Seasonal occurrence of epifauna on test panels in Hampton Roads, Virginia., International Journal of Oceanology and Limnology 1(3): 149-164

Calder, Dale Ralph (1966) <missing title>, M.S. Thesis, College of William and Mary, Williamsburg, VA. Pp. <missing location>

Carlton, James T. (1979) History, biogeography, and ecology of the introduced marine and estuarine invertebrates of the Pacific Coast of North America., Ph.D. dissertation, University of California, Davis. Pp. 1-904

Castagna, M.; Chanley, P. (1973) Salinity tolerance of some marine bivalves from inshore and estuarine environments in Virginia waters on the western mid-Atlantic coast., Malacologia 12(1): 47-96

Conrad, T. A. (1830) On the geology and organic remains of a part of the peninsula of Maryland, Journal of the Academy of Natural Sciences of Philadelphia 6(2): 205-223

Cory, Robert L. (1967) Epifauna of the Patuxent River Estuary, Chesapeake Science 8(2): 71-89

Counts, Clement L. III; Bashore, Terry L. (1991) Mollusca of Assateague Island, Maryland and Virginia: A reexamination after seventy-five years., Veliger 34(2): 214-221

Dall, William Healey (1885) List of marine Mollusca comprising the quaternary fossils and recent forms from American localities between Cape Hatteras and Cape Roque including the Bermudas, Bulletin of the United States Geological Survey 24: 1-336

Dall, William Healey (1889) A preliminary catalogue of the shell-bearing marine mollusks and brachiopods of the south-eastern coast of the United States, Bulletin of the United States National Museum 37: 1-221

Davidson, Ian C.; McCann, Linda D.; Sytsma, Mark D; Ruiz, Gregory M. (2008b) Interrupting a multi-species bioinvasion vector: The efficacy of in-water cleaning for removing biofouling on obsolete vessels., Marine Pollution Bulletin 56: 1538-1544

Davies, Tudor T. (1972) Effect of environmental gradients in the Rappahannock River estuary on the molluscan fauna, Memoirs of the Geological Society of America. 133: 263-290

De Kay, James E. (1843) Mollusca, Vol. 5, Zoology of New-York., In: (Eds.) Zoology of New-York. , Albany. Pp. <missing location>

Ferguson, F. F.; Jones, E. R. (1949) A survey of the shoreline fauna of the Norfolk Peninsula., American Midland Naturalist <missing volume>: 436-446

Frey, David G. (1946) Oyster bars of the Potomac., United States Fish and Wildlife Service Special Scientific Report 32: 1-93

García-Cubas, Antonio; Reguero, Martha; Elizarrarás, Rafael (1992) [Mollusks from Chica-Grande lagoon system, Veracruz, Mexico: systematics and ecology], Anales Del Instituto de Ciencias Del Mar y Limnologia 19(1): 71-101

Gosner, Kenneth L. (1971) Guide to identification of marne and estuarine invertebrates., In: (Eds.) . , New York. Pp. <missing location>

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Humphries, Edythe M.; Duedall, Iver W.; Jordan, Stephen J. (1985) Coal-waste blocks as a fouling substrate in estuarine water., In: (Eds.) Energy Wastes in the Ocean. , New York. Pp. 613-649

Jacobson, Morris K.; Emerson, William K. (1971) <missing title>, Dover Publications, Inc., New York. Pp. <missing location>

Johnson, Charles W. (1915) Fauna of New England. 13. List of the Mollusca, Occasional Papers of the Boston Society of Natural History 7: 1-223

Kennedy, Victor S. (1980) Comparison of recent and past patterns of oyster settlement and seasonal fouling in Broad Creek and Tred Avon River, Maryland, Proceedings of the National Shellfisheries Association 70(`): 36-46

Larsen, Peter F. (1985) The benthic fauna associated with the oyster reefs of the James River estuary, Virginia, U. S. A., Internationale Revue der Gesamten Hydrobiologie 70(9): 707-814

Lippson, Alice J.; Haire, Michael S.; Holland, A. Frederick; Jacobs, Fred; Jensen, Jorgen; Moran-Johnson, R. Lynn; Polgar, Tibor T.; Richkus, William (1979) Environmental atlas of the Potomac Estuary, Martin Marietta Corp., Baltimore, MD. Pp. <missing location>

Lippson, Alice Jane; Lippson, Robert L. (1997) <missing title>, Johns Hopkins University Press, Baltimore. Pp. <missing location>

Loveland, Robert E.; Shafto, Sylvia S. (1984) Fouling Organisms, In: Kennish, Michael J., and Lutz, Richard A.(Eds.) Ecology of Barnegat Bay, New Jersey.. , Berlin. Pp. 226-20

Maurer, Don; Watling, Les; Aprill, Glenn (1974) The distribution and ecology of common marine and estuarine pelecypods in the Delaware Bay area, Nautilus 88(2): 38-45

Morris, Percy A. (1975) A field guide to shells of the Atlantic, Houghton-Mifflin, Boston. Pp. <missing location>

Nauman, J. W.; Cory, R. L. (1969) Thermal additions and epifaunal organisms at Chalk Point, Maryland., Chesapeake Science 10(3-4): 218-226

Perkins, George H. (1871) Molluscan fauna of New Haven. A critical review of all the marine, fresh water and land Mollusca of the region, with descriptions of many of the living animals and of two new species. Part II: Acephala and Bryozoa., Proceedings of the Boston Society of Natural History 13: 138-163

Richards, Horace Gardiner (1938) <missing title>, Bruce Humphries, Inc., Boston. Pp. <missing location>

Say, Thomas (1858) <missing title>, H. Bailliere, New York. Pp. <missing location>

Shaw, William N. (1967) Seasonal fouling and oyster setting on asbestos plates in Broad creek, Talbot County, Maryland, 1963-65., Chesapeake Science 8(4): 228-236

Smith, Sanderson; Prime, Temple (1870) Report on the Mollusca of Long Island, N. Y., and of its dependencies, Annals of the Lyceum of Natural History 9: 377-407

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database. <missing description>

Visscher, J. Paul (1927) Nature and extent of fouling of ship's bottoms., Bulletin of the Bureau of Fisheries 43: 193-252

Waselkov, Gregory A. (1982) <missing title>, Ph.D. dissertation, University of North Carolina, Chapel Hill NC. Pp. <missing location>

Wass, Melvin L. (1972) A checklist of the biota of lower Chesapeake Bay, Special Scientific Report, Virginia Institute of Marine Science 65: 1-290

White, Marie E.; Wilson, Elizabeth A. (1996) The Eastern Oyster: Crassostrea virginica, Maryland Sea Grant, College Park. Pp. 559-579

Whyte, Thomas R. (1988) Fish and shellfish use in the woodland period on the Virginia coast, Journal of Middle Atlantic Archaeology 4: 105-120