affinis Poppe (1880)
|Figure 1: A female E. affinis illustrating
the long first antennae and single brood pouch that is typical for calanoid
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
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
affinis exhibits two generations a year. In the Great Lakes
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.
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
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
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.
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.