Zooplankton of the Great Lakes <Home>
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Organism: Chaoborus sp.
Classification and Life History
Chaoborus, also known as The Phantom Midges, are a predacious omnivore that develops sequentially in both aquatic and terrestrial zones in three stages. The first two of these three stages occur in aquatic environments (Diomande et al. 2010). The majority of the life cycle is spent in the larval stage, which can vary from seven days to several months (Diamande et al. 2010; Berendonk et al. 2009; VonEnde 1982), while the nymphal stage will last only 2-4 days (Diamande et al. 2010). The imago stage of development occurs in the air, and generally lasts for less than 10 days (Diamande et al. 2010) (Figure 1). Some species of Chaoborus (C. punctipennis) have been seen to have two generations per year, one overwintering-spring generation and a summer generation (Eaton 1983).
Figure 1. Development stages of Chaoborus sp. from egg to adult (Berendonk et al. 2009).
Habitat Selection and Behavior
Many zooplankton species will exhibit a behavior called Diel Vertical Migration (DVM). This occurs when a zooplankton is near the bottom of the water column during the daytime, and migrates to the surface near dusk and into the nighttime. Zooplankton may migrate vertically as a result of light, prey abundance, turbidity, and temperature. Larval Chaoborus exhibit DVM in the presence of fish (Stall 1966; Northcote 1964). Interestingly, in the absence of fish Chaoborus do not exhibit DVM (Northcote 1964), which suggests that Chaoborus are able to detect chemical cues (kairomones) from fish and can also detect their absence.
Chaoborus are often consider opportunistic eaters, as they will eat both copepods and cladocerans (Pastorok 1980; Swift and Fedorenko 1975). However, in a laboratory setting, given the choice between the two, Chaoborus prefers the copepods to the cladocerans (Pastorok 1980). In the case of Diaptomus and Daphnia, Pastorok (1980) suggests that this difference may result from the much higher swimming rate of Daphnia. When resources are limited, or copepods are not present, Chaoborus will select Daphnia as an adequate substitute. In most cases, Chaoborus selects the prey that enters it effective stick zone, and does not tend to chase its prey (Swift and Fedorenko 1975). Another factor in feeding is head size. As mandible and head size vary from species to species, prey selection will also vary (Swift and Fedorenko 1975).
While many zooplankton exhibit DVM, Chaoborus is uniquely adapted to migrate vertically even when oxygen is not present. While many zooplaknton require high levels of oxygen to produce ATP, Chaoborus uses an anaerobic malate cycle to derive ATP when oxygen is deprived at the bottom of eutrophic lakes (Maddrell 1998). The ability to function in environments that are oxygen deprived allows Chaborus to further escape predation by simply migrating to areas that fish predators cannot tolerate.
The features of Chaoborus make it easy to distinguish from other zooplankton. Most species of Chaoborus have a long, skinny body cavity with varying amounts of pigmentation (Von Ende 1982). The high density of pigment on Chaoborus americanus, for example, make it better suited for lakes with little to no fish population. Chaborus also features two pair of darkly pigmented air sacks that are used in migration. The expulsion of gas results in the sinking of the organism, while the induction of gas will cause the organism to rise in the water column (Von Ende 1982) (Figures 2, 3).
Chaoborus relies mostly on its mandibles for feeding (Figure 4). The mandibles, which are generally paired, trap and shred prey as they are captured and pushed back through the digestive system (Weddman and Richter 2007). Mandibles vary in size based on species (Weddman and Richter 2007).
Figure 2. Both sets of paired gas sacks under 10x magnification.
Figure 3. Paired gas sacks under 30x magnification.
Figure 4. Head of Chaoborus from top. Manidibles visible on each side of the head.
Berendonk, T. U., Spitze, K., and Kerfoot, W.C. (2009). Ephemeral metapopulations show high genetic diversity at regional scales. Ecology. 90(10): 2670-2675.
Diomande, D., Er, T. T., Franquet, E., Maasri, A., Quattara, A., and Gourene, G. (2010). Temporal dynamics of Chaoborus larvae (Diptera : Chaoboridae) in the tropical ecosystem. Sciences and Nature 7(1): 51-58.
Eaton, K. A. (1983). The life history and production of Chaoborus punctipennis (Diptera: Chaoboridae) in Lake Norman , North Carolina , USA. Hydrobiologia. 106: 247-252.
Fedorenko, A.Y., and Swift, M.C. (1972) Comparative Biology of Chaoborus Americanus and Chaoborus Trivittatus in Eunice Lake, British Columbia. Limnology and Oceanography. 17(5): 721-730.
Maddrell, S.H.P. (1998). Why are there no Insects in the Open Sea? The Journal of Experimental Biology. 201: 2461-2464.
Northcote, T.G. (1964). Use of high-frequency echo sounder to record distribution and migration of Chaoborus larvae. Limnology and Oceanography. 9: 8791.
Pastorok, R.A. (1980). The Effects of Predator Hunder and Food Abundance on Prey Selection by Chaoborus Larvae. Limnology and Oceanography. 25(5): 910-921.
Stahl, J.B. (1966). The ecology of Chaoborus in Meyers Lake, Indiana. Limnology and Oceanography. 11: 177183.
Swift, M.C., and Fedorenko, A.Y. (1975). Some Aspects of Prey Capture by Chaoborus Larvae. Limnology and Oceanography. 20(3): 418-425.
Von Ende, C. N. (1982). Phenology of Four Chaoborus Species. Environmental Entomology. 11(1): 9-15.
Weddman, S and Richter, G. (2007). The Ecological Role of Immature Phantom Midges (Diptera: Chaoboridae) in the Eocene Lake Messel, Germany. African Invertebrates. 48(1): 59-70.