Mesocyclops edax Classification Kingdom - Animalia The name Mesocyclops
edax was originally given to this copepod by Coker (1943). Initially
described as
Cyclops edax by
Forbes (1891), Marsh (1910) reviewed
C. edax
and found that it was not sufficiently different from
C. leuckarti
to comprise a distinct species and it was lumped back in with
C. leuckarti.
Sars (1918) re-listed the genus of
Cyclops leuckarti
to Mesocyclops
and Kiefer (1929) again divided out distinct individuals which he called
M. leukarti edax.
Finally, Coker (1943) was able to provide enough sufficient evidence to
declare M. edax
as a separate species. Because of the shifts in taxonomy Balcer et al
(1984) suggest that C. leuckarti, C. leuckarti edax and
M. leuckarti reported in the great lakes before 1960 may include what
we now know to be M. edax. Anatomy The largest cyclopoid
copepod in the Lake Michigan (Wells 1970), adult CVI females
(Figure 1) range in size between 1.3 -1.7 mm while male CVI (Figure 2) are
a bit smaller ranging between 0.8 – 1.0 (Balcer et al. 1984). According
to Balcer 1984, the best defining characteristics of M. edax are
the “long, palmately spread, terminal setae on the caudal rami” (Figure
1), while Pennak 1978, uses the presence of fine hairs on the inside of
the caudal rami (Figure 3) to distinguish them from other closely related
species. Adult females will often be seen with two egg sacs on either
side of their urosome (Figure 1) while adult males have a geniculated
first antenna (Figure 2). Distribution M. edax
is commonly found throughout North America. It is found in all five great
lakes as well as many other smaller lakes and ponds. Local abundance of
these animals can reach as high as 22,000 per cubic meter
(Balcer et al. 1984) however
other authors have found much lower densities (Selgeby 1975). Presence of
M. edax may be seasonal. It has been reported that they prefer
warmer waters > 8ºC. Samples collected before water warms to this
temperature and after it begins to cool bellow 13ºC may lack M. edax
(Andrews 1953). Habitat Mesocyclops edax is planktonic during the active parts of its seasonal cycle.
Distribution of M. edax is dependant upon water temperature. It
can be found in warmer waters of the littoral zone and pelagic
epilimnion of large bodies of water as well as small lakes and ponds (reviewed by Baler et al 1984). Diapausing M. edax will
stay in or near bottom sediments (Balcer et al. 1984). Feeding Ecology It appears that M. edax
is omnivorous despite an apparent preference for zooplankton prey. M.
edax will prey on a wide variety of invertebrates and may even
prey on vertebrates
(Davis 1959b).
Documented zooplankton prey includes: Diaphanosoma, Daphnia, other
copepods, rotifers, and protazoans (Fryer 1957, Smyly 1961). It, as well as the
closely related M. leuckartii, have also been observed to take
phytoplankton (Smyly 1961, Fryer 1957) and may actively filter them from
the water (reviewed by Balcer et al). Like other zooplankters
M. edax is likely prey for many planktivorous fish species. Wells
(1970) noticed that abundances dropped dramatically after the alewife
population explosion in Lake Michigan. He theorized that alewives were
selectively preying on it because of its large size. Life History Reproduction in M. edax
is sexual. Males use their geniculate first antennae to hold onto females
while attaching a spermatophore or “sperm sac” to the urosome of the
female. Females carry two egg sacks with clutch sizes typically averaging
19-17 eggs (Selgeby 1975). M. edax undergoes development
similar to many other copepods. Eggs will hatch into nauplii (Figure 4) and
molt 4 times while in the naupliar stage until they reach NV (nauplius 5).
At this point nauplii will molt into CI (copepodid 1). There are 4 more
successive molts resulting in a copepodid V. On the final molt M. edax
will become mature adults, CVI. M. edax is bivoltine producing two
generations per year. Individuals will often diapause during winter as CV
and come out in early spring, at which point they will molt into CVI and
reproduce. Young from these adults will mature over the summer, reproduce,
and their offspring will over winter as CV (Selgeby 1975). The
entire life cycle, from egg to adult, may only take 70 days however this
time may be dependant upon environmental conditions food availability (Smyly
1961). Literature cited Andrews, T. F. 1953.
Seasonal variations in relative abundance of Cyclops vernalis,
Cyclops bicuspidatus, and Mesocyclops leuckartii in western
Lake Erie from July, 1946 to may, 1948. Ohio Journal of Science 53:91-100 Balcer, M. D., N. L. Korda,
and S. I. Dodson. 1984. Zooplankton of the Great Lakes. University of
Wisconsin Press, Madison, WI. Davis, C. C. 1959.
Damage to fish fry by cyclopoid copepods.
Ohio Journal of Science
59(2) 101-102. Fryer, G. 1957. The
food of some freshwater cyclopoid copepods-and its ecological
significance. Journal of Animal Ecology 26 263-286. Pennak, R. W. 1978.
Fresh-Water Invertebrates of the United States, Second Edition. John
Willey and Sons, Nex York, New York. Selgeby, J. H. 1975.
Life histories and abundances of crustacean zooplankton in the outlet of
Lake Superior, 1971-1972. Journal of the Fisheries Research Board of
Canada 32 461-470. Smyly, W. J. P. 1961 The
life cycle of the freshwater copepod Cyclops leuckarti Claus in
Esthwaite Water. Journal of Animal Ecology 30 153-169. Wells, L. 1970. Effects of
alewife predation on zooplankton populations in Lake Michigan. Limnology
and Oceanography 15 556-565. |
Figure 1.Ventral view of CVI female with egg sacs. Note the "palmately spread
antennae on the caudal rami".
Figure 2. Dorsal view of adult male CVI. Note the dissected
geniculate antennae. Figure 3. Fine hairs on inside of caudal rami at 400x. Figure 4. Typical cyclopoid nauplius. |