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.

Nitokra incerta
(a harpacticoid copepod)

Copyright Info
Nitokra incerta (Richard, 1893)

Common name: a harpacticoid copepod

Synonyms and Other Names: Nitokra is frequently misspelled as "Nitocra" in literature

Taxonomy: available through www.itis.govITIS logo

Identification: This copepod is part of the large N. lacustris group, which contains a number of subspecies and cryptic species from around the world. In the Great Lakes, all Nitokra species exhibit a 3-segmented exopod on the 1st leg, and the last segment of the exopod has 5 spines. The 5th leg of N. incerta in both sexes is distinct from that in other species that belong to the N. lacustris group in the Great Lakes (Lesko et al. 2003).

Size: 0.5-0.75 mm

Native Range: Nitokra incerta is native to the Black and Caspian Seas region as well as parts of the Jordan River basin, southwest Asia, and Italy (Grigorovich et al. 2001).

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

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, 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 Nitokra incerta are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†

Table last updated 12/5/2023

† Populations may not be currently present.

Ecology: This is an oligohaline species that occurs in fresh and brackish waters in salinities of up to 14.0 ppt (Por 1984; Grigorovich et al. 2001).

Means of Introduction: The species probably arrived in the ballast water of overseas shipping. Duggan et al. (2005) found other Nitokra spp. in ballast water of ships entering the Great Lakes, although N. incerta was not present.

Status: Established in L. Michigan (USEPA 2008).

Impact of Introduction:

A) Realised: The introduction of N. incerta and its nonindigenous congener N. hibernica is likely responsible for the introduction to Lake Erie and the Detroit River of the suctorian ciliate Acineta nitocrae, which is a epizooic on these two copepod species in the Ukraine (Grigorovich et al. 2001).

B) Potential: Unknown.

Remarks: May not be established as there have been no reports of N. incerta since Grigorovich et al. (2001) (Reid and Hudson 2008).

Moreover, after conducting numerous measurements and observations of Nitokra spp. across the Great Lakes, P. Hudson (pers. comm.) has not been able to find reliable, consistent morphological characters to possible separate N. incerta from N. hibernica, suggesting that these proposed congeners may be synonymous.

References: (click for full references)

Duggan, I.C., C D.A. van Overdijk, S.A. Bailey, P.T. Jenkins, H. Limen, and H.J. MacIsaac. 2005. Invertebrates associated with residual ballast water and sediments of cargo-carrying ships entering the Great Lakes. Canadian Journal of Fisheries and Aquatic Sciences 62: 2463-2474.

GLMRIS. 2012. Appendix C: Inventory of Available Controls for Aquatic Nuisance Species of Concern, Chicago Area Waterway System. U.S. Army Corps of Engineers.

Grigorovich, I.A., I.V. Dovgal, H.J. MacIsaac, and V.I. Monchenko. 2001. Acineta nitocrae: a new suctorian epizootic on nonindigenous harpacticoid copepods, Nitocra hibernica and N. incerta, in the Laurentian Great Lakes. Archiv fuer Hydrobiologie 152(1): 161-176.

Lesko, L.T., P.L. Hudson, J.W. Reid, and M.A. Chriscinske. 2003. Harpacticoid copepods of the Laurentian Great Lakes. Great Lakes Science Center, Ann Arbor, Michigan. http://www.glsc.usgs.gov/greatlakescopepods/Key.asp?GROUP=Harpacticoid

Por, F.D. 1984. An outline of the distribution patterns of the freshwater Copepoda of Israel and surroundings. Hydrobiologia 113: 151-154.

Reid, J., and P.L. Hudson. 2008. Comment on "Rate of species introductions in the Great Lakes via ships ballast water and sediments." Canadian Journal of Fisheries and Aquatic Sciences 64: 549-533.

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 http://www.epa.gov/ncea.

Other Resources:
Great Lakes Water Life

Author: Kipp, R.M., J. Larson, T.H. Makled, and A. Fusaro

Revision Date: 9/12/2019

Citation Information:
Kipp, R.M., J. Larson, T.H. Makled, and A. Fusaro, 2023, Nitokra incerta (Richard, 1893): U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=2373, Revision Date: 9/12/2019, Access Date: 12/5/2023

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.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2023]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [12/5/2023].

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