Zooplankton of the Great Lakes
Site created by: Margaret Van Guilder
Organism: Moina micrura
Species: Moina micrura
The cosmopolitan Moina micrura is argued to be not a single species, but rather a cryptic species complex (Martínez-Jerónimo et al., 2007).
Approximately 0.5 mm in length, Moina micrura (Figure 1) is relatively rounded in body shape, yet possesses a relatively large, distinct head (Balcer et al., 1984). The head is approximately ½ the length of the body and is curved or sloped ventrally (Figure 2). The first antennae are exposed (not covered by a beak), variable in length, flexible and are attached along the ventral surface of the head, rather than at the front (Figure 1). The tips of the antennae are blunt and exhibit short olfactory setae. The second antennae are large and used for swimming. The body is surrounded by a shell-like carapace which is open along the ventral surface and includes a notch-like cervical sinus (near the “nape”) on the dorsal surface of the body. The dorsal surface also includes a brood chamber to carry eggs (Figure 1). Moina micrura lacks a rear shell spine, rostrum and ocellus, or eye spot, though does exhibit a single large, median compound eye. M. micrura does exhibit a post-abdominal claw with pecten of uniform length (Figures 3 and 4). Dorsal to the postabdomen are two pairs of relatively long abdominal setae (Figure 5) (Balcer et al., 1984).
Distribution and Habitat:
Moina micrura is distributed across the globe. Samples have been collected from North America (Balcer et al., 1984; Martínez-Jerónimo et al., 2007), Europe (Crosetti and Margaritora, 1987), South America (Fileto et al., 2004; Fileto et al., 2010), Africa (Hart, 1990) and Southeast Asia (Jana and Pal, 1985). M. micrura is rarely found inhabiting the Great Lakes, though it has been found in Lake Michigan near Green Bay (Balcer et al., 1984). It has been shown to inhabit temporary pools that are often highly eutrophic and have shallow depth (Crosetti and Margaritora, 1987). Relatively turbid lakes high in nutrients tend to encourage M. micrura habitation (Hart, 1990; Jana and Pal, 1985).
Moina micrura are filtering grazers of small phytoplankton (Balcer et al., 1984). Feeding occurs when water is moved across the thoracic appendages. Food particles in the moving water are often brought into the carapace. Any floating phytoplankton is trapped by the setae on the thoracic legs and then moved to the mouth to be consumed. Food particles are most often algae, yet can also consist of bacteria, protozoa and organic detritus (Balcer et al., 1984). Food particles are often selected based on size (primarily), shape, chemical cues, taste and nutritional content (Pagano, 2008). Fileto et al. (2004) determined that very small and very large particle are unsuitable for these cladocerans due to a lack of being trapped and an inability to ingest respectively. A suitable upper limit of algae size consumed was determined to be approximately 35 μm with algae 15 μm in length were most abundant in the diet (Fileto et al., 2004). Similar results were determined by Pagano (2008), though algal abundance in the diet (based on size) differed and was varied.
Life History/ Growth and Reproduction:
Moina micrura individuals, like other cladocerans, molt in order to allow for body growth (Balcer et al., 1984). As the old shell is removed, water is taken in to increase body volume before the new exoskeleton hardens. Molting occurs many times throughout the life span of M. micrura. M. micrura exhibits cyclic parthenogenetic reproduction in which during favorable conditions, adult females produce unfertilized eggs which are deposited into the brood chamber following a molt. These eggs develop into juvenile females which are released from the brood chamber at the next molt. The free swimming juveniles then molt and grow several times, ultimately reaching adulthood. When conditions become adverse, a female will produce special eggs that develop into males. Once these males reach maturity, the females will produce haploid eggs which are then fertilized by the males. The eggs are then released when the female molts and are encased in the carapace. This complex is called an ephippium and is resistant to adverse conditions. Once conditions are favorable, the fertilized eggs hatch to release parthenogenetic female offspring (Balcer et al., 1984; Martínez-Jerónimo et al., 2007). Figure 6 shows this as generalized cladoceran lifecycle. Adult longevity is approximately 12 days in the wild and reproductive peak occurs between five and ten days (Jana and Pal, 1985).
Adverse conditions leading to sexual reproduction are varied and include zooplankton density, temperature, adequate food quality and quantity and photoperiod among others (Martínez-Jerónimo et al., 2007). Crosetti and Margaritora (1987) determined that M. micrura populations in Castelporziano Park, Italy were most prevalent between May and August, and that sexual reproduction was most likely induced by temperature and photoperiod, as well as competition. Martínez-Jerónimo et al. (2007) determined that volume of the container used in lab experiments of cultured M. micrura was a significant inducer of sexual reproduction. Jana and Pal (1985) determined that varying nutrient cultures (food quality) had a large impact on growth and reproduction of M. micrura. They determined that while egg incubation was relatively similar across media, longevity, number of parthenogenetic females produced by a single female, and peak reproduction days varied greatly (Jana and Pal, 1985).
Figure 1. Whole mount of M. micrura.
Figure 2. M. micrura head, indicating the ventral sloping as well as the large compound eye.
Figure 3. Post-abdominal claw still within the body.
Figure 4. Post-abdominal claw dissected from body to show detail.
Figure 5. Posterior end of M. micrura exhibiting the post abdominal setae.
Figure 6. Generalized cladoceran life cycle (Ebert, 2005).
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 Crustacean Species. The University of Wisconsin Press. Madison, Wisconsin.
Crosetti, D. and F.G. Margaritora. 1987. Distribution and life cycles of cladocerans in temporary pools from central Italy. Freshwater Biology. 18:165-175
Ebert, D. 2005. Introduction to Daphnia Biology. (http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=daph&part=ch2)
Fileto, C., M.S. Arcifa, A.S. Ferrão-Filho and L.H.S. Silva. 2004. Influence of phytoplankton fractions on growth and reproduction of tropical cladocerans. Aquatic Ecology. 38:503-514
Fileto, C., M.S. Arcifa, R. Henry and R.A.R. Ferriera. 2010. Effects of temperature, sestonic algae features, and seston mineral content on cladocerans of a tropical lake. International Journal of Limnology. 36:135-147.
Hart, R.C. 1990. Zooplankton distribution in relation to turbidity and related environmental gradients in a large subtropical reservoir: patterns and implications. Freshwater Biology. 24:241-263.
Jana, B.B. and G.P. Pal. 1985. Life history parameters of Moina micrura (KURZ.) grown in different culturing media. Water Research. 19:863-867
Martínez-Jerónimo, F., J. Rodríguez-Estrada, R. Villaseñor-Córdova. 2007. Effect of culture density and volume on Moina micrura(Kurz, 1874) reproduction, and sex ratio in the progeny. Hydrobiologia. 594:69-73
Pagano, M. 2008. Feeding of tropical cladocerans (Moina micrura, Diaphanosoma excisum) and rotifer (Brachionus calyciflorus) on natural phytoplankton: effect of phytoplankton size–structure. Journal of Plankton Research. 30:401-414