Skistodiaptomus pallidus
Skistodiaptomus pallidus
(calanoid copepod)
Native Transplant
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Skistodiaptomus pallidus Herrick, 1879

Common name: calanoid copepod

Synonyms and Other Names: Diaptomus pallidus

Taxonomy: available through www.itis.govITIS logo

Identification: The endopod of the 1st leg of this copepod species is bifurcate. Unlike some other diaptomids, the antepenultimate segment of the right 1st antenna has no distinct appendage and is not produced into a blunt point in males. The male left 5th leg is shorter than the right, reaching to the end of or slightly past the 1st segment of the right exopod. There is a scythe-like inner process on the terminal exopod segment of the male left 5th leg. Females have 3 urosomal segments, rounded metasomal wings with small sensilla, and a somewhat expanded genital segment (Pennak 1989; Lesko et al. 2003).

Size: Females are around 0.8–1.2 mm long while males are around 0.7–1 mm long (Geddes and Cole 1981; Torke 2001; Lesko et al. 2003).

Native Range: Skistodiaptomus pallidus is native to the north central plain states, northeast to New York, southern United States in the Mississippi River basin, Texas, and west to Colorado (Pennak 1989; Mills et al. 1993; Torke 2001; Thum and Sternberger 2006).

See Remarks for important details.

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Nonindigenous Occurrences: Skistodiaptomus pallidus was first recorded from Lake Ontario in 1967. In the 1970s, it was recorded from Lake Erie, Lake St. Clair, Lake Huron and the Saginaw River. The occurrences in the Lake Huron drainage were discovered upon re-examining archived specimens from 1974 and 1975 (Mills et al. 1993; Torke 2001; Lesko et al. 2003). Unspecified locations in Georgia, North Carolina, and South Carolina (McLaughlin et al., 2005). Collected from Lake Tahoe, on the California and Nevada border in 1979 and several other California locations (Byron and Saunders 1981).  Skistodiaptomus pallidus has expanded its range in North America westward (Duggan et al. 2006).  It has been introduced outside of North America, possibly via the aquarium trade.

Ecology: Found in freshwater lakes. Skistodiaptomus pallidus occurs in beta-mesotrophic to eutrophic habitats with higher total phosphorus and total nitrogen in comparison with those inhabited by two congeners in the United States, S. pygmaeus and S. oregonensis. Skistodiaptomus pallidus can also tolerate more suspended solids and greater turbidity than the latter two. Skistodiaptomus pallidus is typically found in waters with a pH range of 7.5–8.6 and a conductivity range of 77–660 μS cm-1. This species prefers to dwell in cool waters <12ºC and was found at 10 m in June and below 16 m in July, underneath the thermocline in Belews Lake, North Carolina (Chapman et al. 1985; Marcogliese and Esch 1992; Torke 2001; Thum and Stemberger 2006).            

Skistodiaptomus pallidus produces some eggs that go through a diapause stage before they hatch and some that do not. Breeding in general takes place from around March to November and females can produce up to around 20 eggs per brood. Diapausing eggs produced between June and October hatch from December to June of the following year. When production of diapausing eggs occurs in the summer it may aid populations to avoid fish predation. These eggs have been known to reach densities of 105 per m2 in the sediments of some habitats. Such high densities may help mitigate the effects of a poor year in reproduction and recruitment. It may take around 7 weeks for resting stages to hatch. One study found that it takes around 66 days at 10ºC and 15 days at 25ºC for development to the adult stage. There are 2–5 generations per year in different parts of this species’ range (Geiling and Campbell 1972; Chapman et al. 1985; Dowell 1997; Torke 2001; Lesko et al. 2003; Wonham et al. 2005).            

Skistodiaptomus pallidus feeds on phytoplankton, especially individual algae >53 μm in size. It can also selectively and intensely prey on some rotifer species (Geiling and Campbell 1972; Williamson and Butler 1986; Torke 2001).            

Skistodiaptomus pallidus has been known to reach densities of 10,000 individuals per m3 in a coastal marsh in Lake Erie (Krieger and Klarer 1991).

Means of Introduction: Uncertain, however, S. pallidus could have been introduced accidentally in bait buckets, in fishing equipment, by recreational boaters, with hatchery stock from the Mississippi River basin, or through dispersal (Mills et al. 1993; Lesko et al. 2003; Reid and Hudson 2008).

Status: Considered established, but see Remarks.

Impact of Introduction: Potential:
Skistodiaptomus pallidus is an efficient omnivorous predator, with the ability to prey on preferred rotifers and microzooplankton from large distances. It also consumes algae and practices cannibalism, which may allow populations to persist when resource availability is low (Williamson and Butler 1986; Williamson and Vanderploeg 1988). It has also been known to attain very high densities in suitable habitats, reaching 10,000 per m3 in a Lake Erie marsh to unknown consequences (Krieger and Klarer 1991). Skistodiaptomus pallidus became the primary calanoid copepod in a particularly eutrophic portion of Lake Tahoe, dominating two previously common species, Leptodiaptomus tyrrelli and Epischura nevadensis (Byron and Saunders 1981).

Additionally, based on evidence from an Ohio lake, it has been suggested that S. pallidus is an intermediate host for the parasitic worm Tanaorhamphus longirostris, although study of this occurrence has been limited (Hubschman 1983). Documented evidence combined with its record of spread across the U.S. (Byron and Saunders 1981) have led some recently colonized areas, like New Zealand, to express concern over the potential effects of S. pallidus on native ecosystems (Duggan et al. 2006).

Remarks: There have been no recent records of this species in the Great Lakes. Persistent populations of S. pallidus may be lacking in the main water bodies of the Great Lakes, although individuals are probably washed into the lakes during floods.  Its native range could extend into tributaries and coastal wetlands within the basin (Mills et al. 1993; Lesko et al. 2003; Reid and Hudson 2008). 

References: (click for full references)

Byron, E.R., and J.F. Saunders III. 1981. Colonization of Lake Tahoe, California, Nevada, USA and other western habitats by the copepod Skistodiaptomus pallidus (Calanoida). Southwestern Naturalist 26(1): 82-83.

Chapman, M.A., J.D. Green, and T.G. Northcote. 1985. Seasonal dynamics of Skistodiaptomus pallidus Herrick and other zooplankton populations in Deer Lake, S.W. British Columbia. Journal of Plankton Research 7(6): 867-876.

Dowell, K.M. 1997. Evidence for diapause in the freshwater copepod Skistodiaptomus pallidus. American Midland Naturalist 137(2): 362-368.

Duggan, I.C., J.D. Green, and D.F. Burger. 2006. First New Zealand records of three non-indigenous zooplankton species: Skistodiaptomus pallidus, Sinodiaptomus valkanovi, and Daphnia dentifera. New Zealand Journal of Marine and Freshwater Research 40: 561-569.

Geddes, M.C., and G.A. Cole. 1981. Variation in sexual size differentiation in North American diaptomids (Copepoda: Calanoida): does variation in the degree of dimorphism have ecological significance? Limnology and Oceanography 26(2): 367-374.

Geiling, W.T., and R.S. Campbell. 1972. The effect of temperature on the development rate of the major life stages of Diaptomus pallidus Herrick. Limnology and Oceanography 17: 304-307.

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

Hubschman, J.H. 1983. Diaptomus pallidus Herrick, 1879 (Crustacea: Copepoda) as an intermediate host for Tanaorhamphus longirostris (Van Cleave, 1913) (Acanthocephala: Neoechinorhynchidae). Journal of Parasitology 69(5): 930-932.

Krieger, K.A., and D.M. Klarer. 1991. Zooplankton dynamics in a Great Lakes coastal marsh. Journal of Great Lakes Research 17: 255-269.

Lesko, L.T., P.L. Hudson, and M.A. Chriscinske. 2003. Calanoid copepods of the Laurentian Great Lakes. Ann Arbor, MI, Online at

McLaughlin, P.L., and 39 others. 2005. Common and scientific names of aquatic invertebrates from the United States and Canada—Crustaceans. American Fisheries Society Special Publication 31, Bethesda, Maryland, American Fisheries Society, 545 p.

Marcogliese, D.J., and G.W. Esch. 1992. Alterations of vertical distribution and migration of zooplankton in relation to temperature. American Midland Naturalist 128(1): 139-155.

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.

Pennak, R. 1989. Fresh-water Invertebrates of the Unites States, 3rd ed. Protozoa to Mollusca. John Wiley & Sons, Inc., New York, New York State. 628 pp.

Reid, J.W., and P.L. Hudson. 2008. Comment on “Rate of species introductions in the Great Lakes via ship’s ballast water and sediments. Canadian Journal of Fisheries and Aquatic Sciences 65(3): 549-553.

Thum, R.A. and R.S. Stemberger. 2006. Pure spatial and spatially structured environmental variables explain Skistodiaptomus copepod range limits in the northeastern USA. Canadian Journal of Fisheries and Aquatic Sciences 63(6): 1397-1404.

Torke, B. 2001. The distribution of calanoid copepods in the plankton of Wisconsin Lakes. Hydrobiologia 453-454: 351-365.

Williamson, C.E., and N.M. Butler. 1986.  Predation on rotifers by the suspension-feeding calanoid copepod Diaptomus pallidus.  Limnology and Oceanography 31: 393-402.

Williamson, C.E., and H.A. Vanderploeg. 1988. Predatory suspension-feeding in Diaptomus: prey defenses and the avoidance of cannibalism. Bulletin of Marine Science 43(3): 561-572.

Wonham, M.J., S.A. Bailey, H.J. MacIsaac, and M.A. Lewis. 2005. Modelling the invasion risk of diapausing organisms transported in ballast sediments. Canadian Journal of Fisheries and Aquatic Sciences 62: 2386-2398.

Other Resources:
Great Lakes Water Life

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

Revision Date: 6/1/2013

Citation Information:
Kipp, R.M., A.J. Benson, J. Larson, T.H. Makled, and A. Fusaro, 2017, Skistodiaptomus pallidus Herrick, 1879: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 6/1/2013, Access Date: 9/25/2017

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.

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Citation information: U.S. Geological Survey. [2017]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [9/25/2017].

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