Zooplankton of the Great Lakes
Chydorus sphaericus
Kingdom:         Animalia
Phylum:           Arthropoda
SubPhylum:     Crustacea
Class:              Branchiopoda
Order:             Cladocera
Family:            Chydoridae
Genus:           Chydorus
Species:         sphaericus
                       Muller 1785


Figure 1: Chydorus sphaericus  note the round to oval appearence, with no noticable appendages outside the carapace.


Chydorus sphaericus has a worldwide distribution from the equator to the Arctic Circle. It is the most common of all Clodecera and currently found within all the Great Lakes. Abundence of this species maybe underestimated due to using to large a mesh size >220 mm while sampling and only taking water samples from the upper water column. Selgeby (1975) found Lake Superior to have Chydorus numbers < 1 m3, while moderate numbers (8000-15,000 organisms/m3) where found in Lake Huron (Watson and Carpenter 1974), Ontario (McNaught and Buzzard 1973), and Michigan (Gannon 1972, Stewart 1974) and is occasionally quite abundant (3,000 – 30,000 organisms/m3). The highest recorded abudence of Chydorus sphaericus was 1,400,000 organisms/m3  within certain lake bottoms ( Fryer 1968).  Chydorus sphaericus is present throughout the year only in Lake Erie, but is generally only found within the remaining Great Lakes in the late summer to late fall (Watson and Carpenter 1974). The highest densities of Chydorus sphaericus have been recorded during the August and November time frame (Davis 1954, 1962, Bradshaw 1964, Rolan et al. 1973, Britt et al. 1973, Beeton and Barker 1974, Gannon 1974, Stewart 1974, Watson and Carpenter 1974  Chydorus sphaericus lives in the littoral zones near the shoreline. It is closely related to algae present which is one of it’s major food sources (i.e Anabaena) This organism can live in a wide array of pH levels ranging from 3.4 to 9.5. Chydorus sphaericus can also with stand varying levels of dissolved oxygen with a recorded low of 0.36mg/L (Fryer 1968).



- Spherical carapaces enclosing limbs and body, round to oval in shape, sometimes punctate or with elevations.
- First antennae are covered by projections that unite to form a “beak”
- Second antennae are biramous with three segments each
- Olfactory setae present on first antennae and used to identify Chydorus to species level.
- Olfactory setae inserted at the end of the first antennule
- Smallest of the Chydorus species found within the Great Lakes. (Females = 0.3 – 0.5 mm/ Males = 0.2 mm)
- Pigmented carapace (Color light yellow to dark brown)
- Hooded head
- Has both a large ocellus and compound eye.
- Rostrum long and acute
- Fornices gradually narrowing into rostrum
- Shell usually reticulated, sometimes smooth
- Postabdomen 8 to 9 marginal denticles 
- Claws small, proximal base spine very minute

Figure 2:  Female Chydorus sphaericus with a brood pouch containing one egg.


Habitat –

Chydorus sphaericus is a nearshore (littoral) organism (Bigre 1893, Wilson 1960, Czaika 1974, Stewart 1974) found within all lentic systems or varying sizes. It can swim well for only short distances, but is most likely to be found clinging to various filamentous algae with its modified limbs (Birge 1897, Fryer 1968). Chydorus is generally found within lakes of higher eutrophication and on or near the bottom sediments. Studies have suggested that this organism migrates away from the bottom sediments after dark to feed within the general safety of low light (Evans and Stewart 1977). 

Feeding – 

- Two distinct feeding manners. 
A. filter feed for small particles of algae and detritus.
B. Attach to large algal filaments and scrape off detritus and diatoms. 
- Eats up to 2.1% of its own body weight per day. 

Ecological Importance –
Cladocerans (i.e. Bosmina and Chydorus) are worthy of much attention because of their importance within various food and energy relationships, especially within lakes and ponds. All carnivorous fish pass through a (larval) early stage in which zooplankton is the major food source. 


Life History
Davis (1962) while conducting a sampling found that during the month of October the population was composed of up to 50% immature adults, and only 8% of the total adult females were carrying eggs within the brood pouch. Chydorus survive the winter months as adults and are capable of reproducing under the ice and they show no periodicity in their reproductive pattern. Chydorus population maxima are not directly related to physical factors such as light and temperature but are related to relative abundance of algae species present.

Predation of Chydorus by fish -
- Largemouth Bass
- Yellow Perch
- Mosquitofish
- Bullheads
- Redhorse
- Carpsuckers

Predator Avoidance – 

Invertebrate predators detect their prey by mechanoreceptors. Prey that produce little turbulence are more difficult to detect, therefore Bosmina and Chydorus take advantage of this fact when they are pursued by predatory Copepods by tucking their antennae into the carapace opening and “playing dead man”. This allows them to sink slowly, producing little turbulence as they avoid predation.

Figure 3: Comparison of Chydorus sp. body size to a Bosmina sp., also note the brood pouch is clearly evident with one egg present on the dorsal side of the female Chydorus sp

Research involving Chydorus:

Deneke, R. 2000. Review of rotifers and crustaceans in highly acidic environments of pH values 3. Hydrobiologia 433: 167-172. 

Duigan, C. A. and H. H. Birks, 2000. The late glacial and early Holocene palaeoecology of cladoceran microfossil assemblages at Krakenes, western Norway, with a qualitative reconstruction of temperature changes. Journal of Paleolimnology. 23 (1) :67-76.

Garcia, B. E. 1999. Food of introduced mosquitofish: Ontigenetic diet shift and prey selection. Journal of Fish Biology 55 (1) :135-147.

Meyers, D. G. 1984 Egg development of a Chydorid cladoceran, Chydorus sphaericus exposed to constant and alternative temperatures significant to secondary productivity in fresh water. Ecology 65, 309-320.

Wollmann, K., R, Deneke, B. Nixdorf, and G. Packroff. 2000. Dynamics of planktonic food webs in three mining lakes across a pH gradient (pH 2-4). Hydrobiologia 433: 3-14. 


Literature Cited:
Balcer, M. D., N. L. Korda, and S. I. Dodson. 1984. Zooplankton of the Great Lakes, A guide to the identification and Ecology of the common Custacean species. The University of Wisconsin Press 174pp. 

Lampert, W. and U. Sommer. 1997. Limnoecology: The Ecology of Lakes and Streams. Oxford University Press, New York 382pp. 

Reed, G. K. and R. D. Wood. 1976. Ecology of Inland Waters and Estuaries. Van Nostrand Inc., New York. 485pp. 

Ward, H. B., G. C. Wipple, Ed. W. T. Edmonson. 1918. Freshwater Biology Second Edition. John Wiley and Sons, Inc. New York. pp 603.