Zooplankton of the Great Lakes
Eurytemora affinis Poppe (1880)

Figure 1:  A female E. affinis illustrating the long first antennae and single brood pouch that is typical for calanoid copepods.
I.  Classification
  Kingdom- Animalia
  Phylum- Arthropoda
  Subphylum- Crustacea
  Class- Maxillopoda
  Subclass- Copepoda
  Order- Calanoida
  Family- Temoridae
  Eurytemora affinis

II. Ecology
     
    A. Distribution: Eurytemora affinis is a euryhaline(occuring in salt, brackish and freshwater) species of calanoid copepod that has been reported from Europe, Asia and North America.  E. affinis is the only species found in the Great Lakes and was first discovered in Lake Ontario in 1958; it has since spread into the upper lakes.  In North America this species of copepod has also been found in the Gulf of Mexico and coastal areas of the Atlantic and Pacific oceans.  Most of the studies have been done in Germany, France, the Caspian and Baltic Seas, and Britain (Balcer et.al., 1984).

    B. Habitat:  In the Great Lakes E. affinis is found at high concentrations in warm epilimnetic and littoral waters.  Some studies have suggested that this species is an epibenthic species that displays diurnal migration patterns in which 60% of the population enters the water column at night (Balcer et. al., 1984).

    C. Feeding Ecology:  E. affinis has been characterized as a filter feeder of nannoplankton in the Great Lakes, but European studies suggest that this species is an omnivore based on its mouth part structure.  In the Great Lakes studies have shown that this copepod can consume nannoplankton at a rate of 0.299 ml/ animal/hour (McNaught et al. 1980).  Their preferred particle size is in the range of 19 to 33 um in diameter (Richman et al. 1980).
 


III.  Life History
       A. Reproduction:
                  Eurytemora affinis undergoes obligate sexual reproduction in which there are females with eggs and all copepodid stages observed between July and September.  Therefore, it makes it difficult to understand the actual number of generations produced each year.  In some coastal populations E. affinis exhibits two generations a year.  In the Great Lakes E. affinis overwinters as eggs that begin hatching in April and mature fast as evident with large numbers of adults in June. Egg development time has been shown to be greatly influenced by water temperature. 

      B. Growth:
Eurytemora affinis development shows naupliar size to range from 0.1 mm (N1) to 0.4 mm (N6).  In Lake Michigan, copepodids (CI-CV) sizes range from 0.4 mm to 1.9 mm respectively (Hawkins and Evans 1979).  Mature female E. affinis can grow to lengths of  1.1 to1.5 mm long, while males typically are smaller at lengths of 1.0 to 1.5 mm long.  In Lake Michigan copepodids have a dry weight of 0.5 1.9 ug, while adults have a dry weight of 3.9-5.3 ug.

IV.  Anatomy
            The first antennae often reach to the caudal rami or at least beyond the metasome (Fig. 1).  These copepods typically have a cigar-shaped body with females having only a single egg sac (Fig.1) and males having only a right geniculated first antennae (Fig. 2)  The males have a modified fifth leg for grabbing females and have a claw on the right leg to maintain their mate.  The family Temoridae contains three North American representatives that include Epischura, Eurytemora and Heterocope. Eurytemora have long caudal rami that end in five terminal setae hairs.  The females are characterized by  having wings on the last metasomal segment (Fig. 3).  The males are characterized by having a modified fifth leg that is crossed as if it were sitting indian-style (Fig. 4). 

Works Cited:
Balcer, Mary D., Korda, Nancy L. and Dodson, Stanley.  1984.  A guide to the Indentification and Ecology of the common crustacean species.  The University of Wisconsin Press.  Madison, WI.

Czaika, Sharon C.  1982.  Indentification of Nauplii N1-N6 and Copepods CI- CVI of the Great Lakes Calanoid and Cyclopoid Copepods.  Great Lakes Research 8(3):  439-469.
 


Figure 2:  A male E. affinis illustrating the long caudal rami with terminal setae and right geniculate first antennae, typical in calanoid copepods.

 

Works Cited Continued:
McNaught, D. C., M. Buzzard, D. Griesmer, and M. Kennedy.  1980.  Zooplankton grazing and population dynamics relative to water quality in southern Lake Huron.  U.S. Environmental Protection Agency, Ecological Research Service. EPA-600/3-80-069.

Richman, S., S. A. Bohon, and S. E. Robins.  1980.  Grazing interactions among freshwater calanoid copepods.  In evolutionand ecology of zooplankton communities, W. C. Kerfoot, ed., pp.219-233. U. Press of New England, Hanover, New Hampshire.

Hawkins, B. E., and M. S. Evans.  1979.  Seasonal cycles of zooplankton biomass in southeastern Lake Michigan.  Journal of Great Lakes Research.  5(3-4): 256-263.

 


 


Figure 3:  The winged metasomal segment of a female Eurytemora affinis

 


Figure 4:  The fifth leg in a male E.affinis is crossed as if it were sitting indian-style.