TABLE 10 Reports of Eubosmina coregoni in the Great Lakes Sampling Date Abd' Reference Sampling Date Abd' Reference LAKE 1967 A Davis 1968 LAKE 1973-1974 p Torke 1975 ERIE 1967-1968 c Davis 1969 MICHIGAN 1974 p Evans and Stewart 1977- 1968, 1970 A Heberger and Reynolds (continued) 1975-1977 Hawkins and Evans 1979 1977 1970 c Watson and Carpenter 1974 LAKE 1970 p Watson and Carpenter 1971-1972 C-A Rolan et al. 1973 HURON 1974 1971-1972 u Carter 1972 1974 u Basch ct al. 1980 LAKE 1966, 1968 p Wells 1970 1974-1975 C-A McNaught et al. 1980 MICHIGAN 1969-1970 P-C Gannon I 972a 1969-1970 A Gannon 1974 1969-1970 p Gannon 1975 LAKE 1970 c Watson and Carpenter 1971 c Howmiller and Beeton ONTARIO 1974 1971 1972 P-C Czaika l 974a 1971-1972 p Beeton and Barker 1974 1972-1973 c Czaika l 978a 1972-1977 p Evans et al. 1980 1973 p Stewart 1974 LAKE 1971 u Selgeby 1975a SUPERIOR 1973 u Upp er Lakes Ref. Group 1977 1974 p Basch et al. 1980 1979-1980 P-C This study •Abundance Code R = rare U = uncommon P = present C =common A= abundant F = found in fish stmnach contents - = abundance ranking not appropriate less tolerant to eutrophication than B. longirostris, as it is LIFE HISTORY AND ECOLOGY IN OTHER LAKES mainly found in larger, less productive lakes (Gurney 1923). Zhdanova (1969) studied E. coregoni in fresh-water lakes Diurnal migration. No studies of the migration patterns and ponds in Kiev, Russia. He observed parthenogenetic of this species have been reported from the Great Lakes. reproduction from June through August when the water Hutchinson (1967) observed that in other lakes immature temperature ranged from 18 to 23'C. Maximum abun­ forms migrated while the adults did not. The animals came dances of 223000-292000 organisms m' were noted. Males to the surface before dark at rates of 3.8-13.2 cm/hr and and ephippial females appeared in late September when began their descent an hour before dawn at a rate of 22.2 water temperature declined to l5°C. By November, when cm/hr. the water had cooled to 4'C, this species disappeared for the winter and was not observed again until water temperature Feeding Ecology and As Food for Fish. E. coregoni has increased in April. only been reported from the Great Lakes since 1966 (Wells Zhdanova also cultured this species in the lab and ob­ 1970), and little is known about its role in the food chain. served maximum growth rates during the first 5 to 10 days. Like the other bosminids, it is a filter feeder. The filtering, E. coregoni molts once before reaching maturity and then ingestion, and assimilation rates of this species have been once for each brood produced. determined in southern Lake Huron by McNaught et al. Additional information on the life history of this spe­ (1980). These authors suggest that E. coregoni may be cies follows: more susceptible to fish predation in Lake Huron than the embryonic development 2-3 days slightly smaller Bosmina longirostris. sexual maturation 3-7 days interval between egg deposition 2-3 days 70 Life History and Ecology of the Major Crustacean Species no. of broods/female 8-9 from 0.3-0.5 mm and males of 0.2 mm. The other species life span 27-36 days are slightly larger than C. sphaericus (Brooks 1959). progeny /female 44 C. gibbus 5i! to 0.5 mm 1naxi1nun1 molts 7 C. faviformis ~ 0.5-0.6 mm average length, newly hatched 0.26 1nm C. Latus ~ 0.7-0.8 mm maxin1un1 length; fernale 0.54 mm C. globosus 5i! to 0.8 mm, 0 to 0.6 mm average \vet weight; fe1nale 0.019 mg In Lake Michigan, C. sphaericus was found to have a dry weight of 0.8-1.2µ,g (Hawkins and Evans 1979). Chydorus Leach 1843 DISTRIBUTION AND ABUNDANCE Chydorids are distributed worldwide, occurring in waters TAXONOMIC HISTORY of low salinity from near the equator to the Arctic Circle The genus Chydorus contains at least five Great Lakes spe­ (Moore 1952). Each of the species in this genus has a more cies. C . .r,,phaericus is the most well known and has often restricted distribution. been considered a common, easily identifiable species C. sphaericus has been found in all the Great Lakes (Birge 1897). Recent studies (Frey 1980) present evidence (Table 11 ). This species is present in low numbers ( < 1 m·') that there are really several morphologically similar but dis­ in Lake Superior (Selgeby 1975a and this study); in moder­ tinct species in the C. sphaericus group, each with a re­ ate numbers (8000-15000 m') in Lakes Huron (Watson stricted distribution. For convenience, in this study all of and Carpenter 1974), Ontario (McNaught and Buzzard these recently recognized forms will be considered under 1973; Watson and Carpenter 1974), and Michigan (Gannon the old name of C. sphaericus (0. F. Muller) 1785. The 1972a; Stewart 1974); and is occasionally quite abundant other chydorids found in the Great Lakes include C. favi­ (3000-30000 rn-') in Lake Erie (Bradshaw 1964; Rolan et formis Birge 1893, C. globosus Baird 1850, C. latus Sars al. 1973; and Heberger and Reynolds 1977). The abundance 1862, and C. gibbus Sars 189 I. C. gibhus has occasionally of this species in the Great Lakes may be underestimated been recorded as C. rugulosus in the Great Lakes plankton because of the use of plankton nets with meshes 220µ,m or literature (Forbes 1897; Frey 1982). larger and the collection of samples from only the upper layers of the water column. The other species of Chydorus are not as well known DESCRIPTION from the Great Lakes. C. faviformis has only been reported All Chydorus are small cladocerans with spherical cara­ from Lake Huron (Bigelow 1922) while C. latus was col­ paces completely enclosing the body and limbs. The first lected once from Lake Erie (Wilson 1960). C. globosus oc­ antennae are covered by projections of the carapace (for­ curs in low numbers in lakes Huron (Bigelow 1922) and nices) that unite with the rostrum to form a beak (Plate 20). Erie (Langlois 1954, Wilson 1960). Wilson (1960) found The second antennae are biramous with three segments in C. gibbus in Lake Erie while Forbes (1891), Birge (1893), each branch. The species are distinguished by the shape of and Selgeby (1974, 1975a) observed it in littoral samples the body and postabdomen, the pattern of the carapace, and from Lake Superior. the position of the olfactory setae on the first antennae. Variation in these characteristics have been observed in LIFE HISTORY IN THE GREAT LAKES single populations of chydorids (Fryer 1968). Therefore, the detailed keys and descriptions by Scourfield and Hard­ The life history and ecology of C. sphaericus is discussed mg (1941), Brooks (1959), Frey (1959), Smirnov (1966a), in the following sections. The other four species occur in an_d especially Frey ( 1980) should be consulted when identi­ low numbers in the Great Lakes and have not been as well fying chydorids to species. studied. C. sphaericus is present year-round in Lake Erie but is SIZE generally only found in the summer and fall in the other Great Lakes (Watson and Carpenter 1974). Abundance C. sphaericus is the smallest chydorid in the Great Lakes. peaks occur between August and November (Davis 1954, We observed females from 0.3-0.4 mm long in Lake Supe­ 1962; Bradshaw 1964; Rolan et al. 1973; Britt et al. 1973; nor (I 979-1980). Brooks (I 959) reported females ranging Beeton and Barker 1974; Gannon 1974; Stewart 1974; Wat- 71 TABLE 11 Reports of Chydorus sphaericus in the Great Lakes Sampling Date Abd' Reference Sampling Date Abd' Reference LAKE 1882 u Vorce 1882 LAKE 1973-1974 u Torke 1975 ERIE 1926 p Langlois 1954 MICHIGAN 1974 c Evans and Stewart 1977 1928 PF Sibley 1929 (continued) 1975-1977 Hawkins and Evans 1979 1928-1929 PF Wilson 1960 1929 U-PF Ewers 1933 1948-1949, p Bradshaw 1964 LAKE 1902, 1905, p Bigelow !922 1959 HURON 1907 1950-1951 c Davis 1954 1967-1968 LI Pat;oibs 1972 1956-1957 c Davis 1962 1970-1971 p Carter 1972 1961 c Britt et al. 1973 1974-1975 p McNaught et al. 1980 1967 p Davis 1968 1967-1968 c Davis 1969 LAKE 1967 u Patalas 1969 1967-1968 p Patalas 1972 1967-1968 LI Patalas l 972 1968-1970 c Heberger and Reynolds ONTARIO 1970 p Watson and Carpenter 1977 1974 1971-1972 P-C Rolan et al. 1973 1972 p McNaught and Buzzard 1973 LAKE 1888 p Eddy 1927 1972 U-P Czaika l 974a MICHIGAN 1926-1927 p Eddy 1934 1973-1974 p Czaika l 978a 1966, 1968 p Wells 1970 1969-1970 p Gannon 1972a LAKE 1889 Forbes 1891 1969-1970 p Gannon 1974 u 1893 p Birge 1893 1969-1970 p Gannon 1975 SUPERIOR 1928 R Eddy 1934 1971 p Howmiller and Beeton 1971-1972 R-P Selgeby 1975a 1971 1971 p Selgcby 1974 1971-1972 p Beeton and Barker 1974 1973 Upper Lakes Ref. Group 1972-1977 p Evans et al. 1980 u 1977 1973 p Stewart 1974 1979-1980 u This study •Abundance Code R = rare U = uncommon P = present C =common A= abundant F = found in fish stomach contents - = abundance ranking not appropriate son and Carpenter 1974). During an October abundance 1974). This distribution pattern may be due to the influence peak in Lake Erie, the chydorid population was composed of the Fox River, which empties into the southern part of the of 50% immature animals, and only 8% of the adult females bay.