Cordylophora caspia Pallas, 1771

Common Name: Freshwater hydroid

Synonyms and Other Names:

Nadine RoremCopyright Info

Nadine RoremCopyright Info

Identification: This colonial hydroid consists of macroscopic polyps (about 1 mm) connected by a gastrovascular cavity; branching, moss-like in appearance (Pennak1987). Colonies grow up to 5 cm, which varies depending on conditions (Folino 2000).

Size: Colonies to 5 cm, polyps around 1mm.

Native Range: Black and Caspian seas of western Asia.

Great Lakes Nonindigenous Occurrences: San Francisco Bay, California (Mills and Sommer 1995).  Coastal waters of Florida (Carlton and Ruckelshaus 1997).  Illinois River, Illinois (personal communication).  Hudson River, New York (Mills, et al. 1996).  Lake Erie, Ohio (Mills et al. 1993).  Southern Lake Michigan, Illinois (personal communication).  Coastal waters of Washington (Ruiz and Hines 1997). Connecticut River between Hadley, Massachusetts and Hinsdale, New Hampshire (Smith et al. 2002).

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 Cordylophora caspia are found here.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Illinois200720071Lake Michigan
Minnesota200120011St. Louis
New York200720071Seneca

Table last updated 5/25/2018

† Populations may not be currently present.

Ecology: Cordylophora caspia lives in freshwater and brackish or slightly salty habitats.  Colonies grow on hard surfaces including rocks, pilings, and dreissenid mussel shells.  Can consume organisms 2–3 times the size of individual polyps by working together.  May benefit from the expansion of zebra and quagga mussels (providing substrate) and from increased salinity in systems impacted by road salt (preference for higher salinity).

Means of Introduction: Aquarium release in Lake Erie (Mills et al. 1993).  Ballast water in Washington (Ruiz and Hines 1997). 

Status: Established in L. Erie (U.S. EPA 2008)

Great Lakes Impacts: Current research on the environmental impact of Cordylophora caspia in the Great Lakes is inadequate to support proper assessment.

Research in the Great Lakes and Europe indicates that C. caspia has complex relationships with dreissenids. Competition for space (i.e. suitable substrate for colonization) may occur between zebra mussels (Dreissena polymorpha) and C. caspia (Folino 2000, Walton 1996). However, these species have been known to colonize one another; juvenile zebra mussels may use C. caspia as a substrate (Moreteau and Khalanski 1994), while C. caspia may settle on dreissenids (Darling and Folino-Rorem 2009, Folino 2000). An initial survey completed in Chicago harbors found 55% of quagga mussels to be colonized by C. caspia (Berg and Folino-Rorem 2009). In addition, zebra and quagga mussel larvae appear to constitute a large portion of C. caspia diet (Berg and Folino-Rorem 2009), though this is unlikely to limit local dreissenid populations.

Studies have suggested that C. caspia may contribute to the restructuring of benthic and pelagic freshwater communities (Folino 2000). For example, research found that as compared to uncolonized control substrates, the successful inoculation of a substrate with C. caspia resulted in a shift in relative abundance of other invertebrates (Ruiz et al. 1999).

Smith et al. (2002) described C. caspia as a benthic colonial predator that preys upon chironomids and other larval insects. Where the hydroid is sufficiently dense, this could locally reduce the preferred prey of certain fishes. Following a study in Chicago harbors, researchers concluded that while the current impact of C. caspia on fish food availability is likely limited, it has the possibility of becoming significant in combination with the growth of D. bugensis populations. The ecological impacts of C. caspia in the Great Lakes, however, have not yet been thoroughly studied.

Current research on the socio-economic impact of Cordylophora caspia in the Great Lakes is inadequate to support proper assessment.

There are economic costs associated with the biofouling caused by Cordylophora caspia (Folino 2000). However, documentation within the Great Lakes region is limited. Cordylophora has reportedly caused blockages of intake tunnels and filters and colonize docks, piers, and pilings near Chicago harbors of Lake Michigan.

Cordylophora has had degrading effects on cement and mortar at Brazilian power plants (Berg and Folino-Rorem 2009, Folino 2000, Portella and Joukoski 2009).

There is little or no evidence to support that Cordylophora caspia has significant beneficial effects in the Great Lakes.

Management: Regulations (pertaining to the Great Lakes)
There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control of Cordylophora caspia will likely focus on its potential role as a biofouling agent. Cordylophora spp. has been documented colonizing the inner walls of power plants in Europe and the United States (Folino 2000), primarily causing blockages in nozzles and tailpipes of rapid gravity filter beds (RGFs) (Mant et al. 2011).  The menont life-stage of Cordylophora caspia often found in hydroelectric intakes, is both drought and temperature resistant which may prove an obstacle to control.  (Gutierre 2011).  

In estuarine, brackish habitats such as San Francisco Bay on the Pacific and the North American Atlantic coast, nudibranchs such as Tenellia adspersa feed on Cordylophora caspia and other hydroids (Mills and Sommer 1995). However, unlike hydroids, nudibranchs are exclusively sea-dwelling invertebrates (Anderson 1995), and thus are only a source of biological control in brackish areas where the macroinvertebrates’ habitats intersect.

Thermal treatments of >37°C have been proven effective in eradicating colonies of Cordylophora spp. sampled from the walls of power plant intakes (Folino 2000), but are not efficient in water treatment facilities where there is no residual heat energy available (Mant et al. 2011).

Gutierre (2011) found that Cordylophora caspia is completely eradicated at pH levels of 4.0 and 10.0, with increasing survival rates in between, and suggested maintaining pH levels at 10.0 for 6 hours or more by injection of NaOH to reduce and eliminate colonies. Chlorine treatments negatively affect Cordylophora growth, but treatments as high as 5 mg/L for periods of 105 minutes have been unsuccessful in completely eradicating colonies (Mant et al. 2011). Furthermore, chlorine use is highly regulated at water treatment facilities where Cordylophora most frequently cause problems. Hydroids are sensitive to vanadium leeching from slag stones used in riverbank reinforcement, and are sensitive to heavy metals in general, especially mercury, copper, cadmium, and arsenic, though it is unlikely that these will be useful in control (Ringelband and Karbe 1996).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: Smith et al. (2002) noted that C. caspia shows morphological and ecological changes in habitats of lower salinity such as inland freshwaters. For example, growth rates decrease, reproductive rates decrease (sexually and asexually), polyp size changes, population density changes, and cell size and shape is altered (Smith et al. 2002 and references).

Cordylophora caspia is preyed upon by an introduced nudibranch (Tenellia adspersa) (Mills and Sommer 1995).

Cordylophora caspia is thought to be taxonomically synonymous with C. lacustris by many scientific researchers (Folino 2000 and references).

References: (click for full references)

Anderson, R.C. 1995. Nudibranchs: butterflies of the sea. International Zoo Yearbook 34.1: 65-70. Web.

Berg, M.B., and N.C. Folino-Rorem. 2009. Alterations of Lake Michigan benthic communities by the invasive colonial hydroid, Cordylophora caspia: effects on fish prey. Unpublished report. Available:

Carlton, J.T., and M.H. Ruckelshaus. 1997. Nonindigenous marine invertebrates and algae. Pages 187-201 In: Simberloff, D., D.C. Schmitz, T.C. Brown (eds), Strangers in Paradise. Island Press, Washington, D.C.

Darling, J.A., and N.C. Forino-Rorem. 2009. Genetic analysis across different spatial scales reveals multiple dispersal mechanisms for the invasive hydrozoan Cordylophora in the Great Lakes. Molecular Ecology 18:4827-4840.

Folino, N.C. 2000. The freshwater expansion and classification of the colonial hydroid Cordylophora (Phylum Cnidaria, Class Hydrozoa). In Pederson, J. (ed.) Marine Bioinvasions: Proceedings of the First National Conference, January 24-27, 1999. Massachusetts Institute of Technology Sea Grant College Program, Cambridge, MA. pp. 139-144.

Gutierre, S.M. 2012. pH tolerance of the biofouling invasive hydrozoan Cordylophora caspia. Hydrobiologia 671: 91-95.

Mant, R. C., G. Moggridge, and D. C. Aldridge. 2011. Biofouling by Bryozoans, Cordylophora, and Sponges in UK Water Treatment Works. Water Science and Technology 63.9: 1815-822. Web.

Mills, C.E., and F. Sommer. 1995. Invertebrate introductions in marine habitats: two species of hydromedusae (Cnidaria) native to the Black Sea, Maeotias inexspectata and Blackfordia virginica, invade San Francisco Bay. Marine Biology 122:279-288.

Mills, E.L., M.D. Scheuerll, D.L. Strayer, and J.T. Carlton. 1996. Exotic species in the Hudson River basin: a history of invasions and introductions. Estuaries 19(4):814-823.

Mills, E.L., J.H. Leach, J.T. Carlton, and C.L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.

Moreteau, J.C., and M. Khalanski. 1994. Settlings and growth of D. polymorpha in the raw water circuits of the Cattenom Nuclear Power Plant (Moselle, France). Proceedings of the Fourth International Zebra Mussel Conference, Madison, WI, March 1994. pp. 553-574.

Pennak, R.W. 1987. Coelenterata (Hydroids, Jellyfish). Pages 110-123 in Fresh-water Invertebrates of the United States, 3rd edition. John Wiley and Sons, Inc., New York. 628 p.

Portella, K.F., and A. Joukoski. 2009. Biofouling and chemical biodeterioration in hydroelectric power plant Portland cement mortar. Química Nova 32(4):1047-1051.

Ringelband, U., and L. Karbe. 1996. Effects of Vanadium on Population Growth and Na-K-ATPase Activity of the Brackish Water Hydroid Cordylophora caspia. Bulletin of Environmental Contamination and Toxicology 57.1: 118-24. Web.

Ruiz, G.M., and A.H. Hines. 1997. The risk of nonindigenous species invasion in Prince William Sound associated with oil tanker traffic and ballast water management: pilot study. Prepared for the Regional Citizens' Advisory Council of Prince William Sound.

Ruiz, G.M., P. Fofonoff, and A.H. Hines. 1999. Non-indigenous species as stressors in estuarine and marine communities: assessing invasion impacts and interactions. Limnology and Oceanography 44(3, part 2):950-972.

Smith, D.G., S.F. Werle, and E. Klekowski. 2002. The rapid colonization and emerging biology of Cordylophora caspia (Pallas, 1771) (Cnidaria: Clavidae) in the Connecticut River. Journal of Freshwater Ecology 17(3):423-430.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and

Walton, W.C. 1996. Occurrence of zebra mussel (Dreissena polymorpha) in the oligohaline Hudson River, New York. Estuaries 19(3):612-618.

Wurtz, C.B., and S.S. Roback. 1955. The invertebrate fauna of some Gulf Coast rivers.  Proceedings of the Natural Sciences Academy of Philadelphia 107:167-206.

Author: Fuller, P., E. Maynard, D. Raikow, J. Larson, T.H. Makled, and A. Fusaro

Contributing Agencies:

Revision Date: 8/20/2018

Citation for this information:
Fuller, P., E. Maynard, D. Raikow, J. Larson, T.H. Makled, and A. Fusaro, 2019, Cordylophora caspia Pallas, 1771: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 8/20/2018, Access Date: 1/21/2019

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.