McNaught and Hasler (1966) were unable to define distinct cladocerans by their distinct rostrum and oval carapace that migration patterns for the Ceriodaphnia populations they usually terminates in an elongated spine. D. galeata men­ observed. dotae is distinguished from other Daphnia by its ocellus broad pointed helmet (Plate 8), and the very fine, uniforn: Feeding Ecology. Ceriodaphnia, like the other members pecten on the postabdominal claw (not visible at 50 x mag­ of the family Daphnidae, are filter feeders (Brooks 1959). nification). Males are distinguished from females by their O'Brien and De Noyelles (1974) determined the filtering elongate first antennae (Plate 9). rate of C. reticulata in several ponds with different levels Head shape is varible (Plate 10), but the peak of the of phytoplankton. McNaught et al. (1980) found that Lake helmet is generally near the midline of the body. Huron Ceriodaphnia species filtered nannoplankton at a rate of 0.270 ml · animal·• · hour" in Lake Huron. SIZE As Food for Fish and Other Organisms. Ceriodaphnia Brooks (1959) reported adult females ranging from 1.3- are eaten by many species of fish including rock bass, large­ 3.0 mm long while males were much smaller, measuring mouth bass, shiners, carp, mosquito fish, yellow perch, only 1.0 mm. ln Lake Superior we found females from and crappie (Pearse 1921: Ewers 1933; Wilson 1960). An­ 1.5-2.0 mm and males averaging 1.25 mm. The dry weight derson (1970) also found that the copepods Diacyclops of animals from Lake Michigan varies from 2.5-8.9µg thomasi and Acanthocyclops vernalis consume Ceriodaph­ (Hawkins and Evans 1979). nia quadrangula. DISTRIBUTION AND ABUNDANCE Daphnia galeata Sars 1864 mendotae Birge 1918 D. galeata mendotae has been collected from lakes along the West Coast and in the formerly glaciated regions of the United States and Canada. It is also common in mountain TAXONOMIC HISTORY lakes in Central and South America (Brooks 1957). This cladoceran is found in all of the Great Lakes This American Daphnia was first described by Smith (Table 6). It is present in small numbers in lakes Ontario (1874a). He identified it as D. galeata Sars 1864. S. A. and Huron (Patalas 1969, 1972; Carter 1972; McNaught Forbes (1882) decided that the American form more closely and Buzzard 1973), in moderate densities (100-6000 m·') resembled D. hyalina Leydig 1860 and changed its name in lakes Superior and Michigan (Wells 1970; Gannon 1974; accordingly. This classification was used by most Great Selgeby 1974; Stewart 1974; Watson and Wilson 1978), and Lakes researchers until 1922, when Clemens and Bigelow is often quite abundant (average 900-5000 m·', peaks of reported Daphnia longispina Millier from Lake Huron. At 270000 m·') in Lake Erie (Bradshaw 1964; Davis 1968, that time D. longispina was a broadly defined taxon that in­ 1969; Rolan et al. 1973). cluded all Daphnia with uniformly small pectens on the postabdoininal claw. During the next 30-40 years most LIFE HISTORY IN THE GREAT LAKES Daphnia in Great Lakes collections were referred to as D. longispina. (The true identity of these organisms is un­ Adults and juveniles are generally absent or present in very known, but it is generally assumed that the majority were low numbers during the winter and spring months (Wells D. galeata mendotae.) Brooks ( 1957) concluded that the 1960; Gannon 1972a, 1975; Rolan et al. 1973; Stewart American species he examined were more closely related to 1974; Beeton and Barker 1974; Selgeby l975a; Heberger D. galeata than to D. hyalina. To show the geographic and Reynolds 1977). The animals hatch from ephippial eggs substatus of these organisms, he renamed them with the tri­ in early summer and reproduce rapidly, with the population nomial Daphnia galeata mendotae. The name "mendotae" size peaking in late summer or early fall (Davis 196 l; refers to a form of D. longispina var. hyalina Ley dig 1860 Bradshaw 1964; Gannon 1972a, 1974, 1975; Rolan et al. figured in Birge (1918). All recent Great Lakes studies have 1973; Britt et al. 1973; Stewart 1974; Selgeby 1975a; used Brook's system of classification. Heberger and Reynolds 1977). The life cycle of this species is best described by DESCRIPTION Selgeby (1975a), who observed three pulses each year in Lake Superior. The first generation hatches from ephippial The most detailed description of this species is presented by eggs in late spring or early summer. The darkly pigmented, Brooks (1957). Daphnia can be distinguished from other round-headed females reproduce parthenogenetically in 60 Life History and Ecology of the Major Crustacean Species TABLE 6 Reports of Daphnia galeata mendotae in the Great Lakes Sampling Date Abd' Reference Sampling Date Abd" Reference LAKE 1919-1920 F Clemens and Bigelow LAKE 1903, 1905, A Bigelow 1922 ERIE 1922 HURON 1907 1928-1929 CL Wilson 1960 1907 u Sars 1915 1938-1939 AL Chandler 1940 1919-1920 FL Clemens and Bigelow 1949 A Bradshaw 1964 1922 1950-1951 CL Davis 1954 1968 R Patalas 1972 1956-1957 CL Davis 1962 1970-1971 p Carrer 1972 1961 A Britt et al. 1973 1974 u Basch et al. 1980 1962 RF Wolfert 1965 1974-1975 p McNaught et al. 1980 1967 A Davis 1962 1967-1968 Davis 1968 A LAKE 1919-1920 F Clemens and Bigelow Patalas 1972 1968 c 1922 1968, 1970 Heberger and Reynolds ONTARIO c 1927-1928 FL Pritchard 1929 1977 1967 u Patalas 1969 1971-1972 Rolan et al. 1973 C-A 1967 R Patalas 1972 Boucherle and Frederick 1974-1975 C-A 1969-1972 p McNaught and Buzzard 1976 1973 1972 p Czaika I974a LAKE 1881 p Forbes 1882 1972-1973 R Czaika l 978a MICHIGAN 1893 p Birge 1893 1887-1888 PL Eddy 1927 LAKE 1871 Smith 1874b 1954-1955, c Wells 1960 SUPERIOR 1893 p Birge 1893 1958 1928 CL Eddy 1934 Wells and Beeton 1963 1954-1961 F 1933-1934 AL Eddy 1943 1966, 1968 Wells 1970 u 1960 PL Putnam 1963 p Gannon 1975 1969-1970 1964 CL Olson and Odlaug 1966 1969-1970 Gannon 1974 c 1968 p Patalas 1972 p Gannon 1972a 1969-1970 1971-1972 c Selgeby 1975a 1971 Howmiller and Beeton c 1971 c Selgeby 1974 1971 1973 c Upper Lakes Ref. Group 1971-1972 u Beeton and Barker ! 974 1977 1973 Stewart 1974 c 1973 c Watson and Wilson 1978 1974 Evans and Stewart 1977 u 1974 p Basch et al. 1980 1972-1977 p Evans et al. 1980 1979-1980 C-A This study 1975-1977 Hawkins and Evans 1979 'Abundance Code R = rare U = uncon1mon P = present C =common A = abundant F = found in fish stomach contents L =organisms classified as D. !ongispina - = abundance ranking not appropriate early July, producing clutches averaging 7 eggs that develop ECOLOGY IN THE GREAT LAKES into low-hehncted females. This second generation also re­ produces parthenogenetically between July and October. Habitat. D. galeata mendotae is found in many lakes but The clutches are somewhat smaller than those of the first is most common in large, deep, transparent waters (Patalas generation. averaging 5.7 eggs. Strongly helmeted females 1971). It prefers the upper water strata (Brooks 1959) sev­ and nu1nerous males hatch from these eggs. This third gen­ eral meters below the surface during the day (Wells 1960; e~ation reproduces sexually in the fall and produces ephip­ Hebergerand Reynolds 1977). In Lake Michigan D. galeata -pial eggs that overwinter. mendotae is often distributed higher in the water column Males have been observed in October and Nove1nber in than D. retrocurva (Stewart 1974). Lakes Ontario and Michigan (Czaika l 974a; Stewart 1974) D. galeata mendotae has also been found near the bot­ and may con1pose 30% of the population late in the year. tom in Lake Michigan (Wells 1960). Greater concentrations 61 occasionally occur in bottom cores from shallow water to those in the Great Lakes. In addition, they observed than in the overlying water column (Evans and Stewart higher filtering rates at the surface at night than at the noon 1977). Heberger and Reynolds (1977) found this species depths, suggesting that vertical n1igration may be advan­ well adapted to a benthic life, being able to withstand very tageous to feeding. low levels of dissolved oxygen that often occur in the Hall (1964) reprots that this species of Daphnia is very hypolimnion. tolerant to variations in light and alkalinity. In later studies This species is often found in large swarms (up to Hensey and Porter (1977) found that, although D. galea1(1 7 3 2 x 10 m- ) due to the action of the wind and waves mendotae prefers high dissolved oxygen levels, it has a (Boucherle and Frederick 1976). These swarms tend to dis­ broad tolerance for this factor and occasionally occurs in perse rapidly. oxygen-poor regions near the thermocline. Diurnal Migrations. The maximum concentration is of­ ten found at a depth of 10 m during the day (Wells 1960). Daphnia retrocurva Forbes 1882 Juveniles are usually located slightly above the adults in the water column and arrive at the surface first when the upward migration begins 1.5 hours after sunset. Many of the ani­ TAXONOMIC HISTORY mals move down slightly after midnight but return to the surface before settling to their daytime depths an hour be­ The taxonomy of this species has undergone several changes fore sunrise. since it was first described by S. A. Forbes in 1882. Her­ rick (1884) and Birge (1893) recognized the similarity of Feeding Ecology. Daphnia are filter feeders that con­ Daphnia retrocurva to a previously described species and sume small algae (0.8-40.0µ.m) and prefer chlorophytes therefore synonymized D.