Zooplankton

The zooplankton include a number of major taxonomic groups of animals, either for their entire life cycle or for short periods, as in the case of the larval stages of some fishes, polychaetes, crustaceans and molluscs. From among these types of zooplankton by far the most important group are the Crustacea, and of these, the copepods are the most predominant and have thus received most attention (Crisp, 1975). 

Quantitative estimates of the global distribution and biomass of zooplankton are extremely difficult. The routine net sampling techniques probably fail to collect a considerable proportion of the microzooplankton which could itself equal the biomass of the net zooplankton (Pomeroy, 1974). Zooplankton biomass data were summarised for various oceanic and coastal waters by Raymont (1966). It is striking that Mullin (1969) in his survey of the production of zooplankton in the ocean does not himself venture any global estimate. 

Productivity/biomass ratios are strongly dependent both on temperature and food supply. Mullin s (1969) review contains a summary table in which the season and location of the measurements are recorded total production estimates in the literature vary between 4.9 and 70 (or 234) mg C m day . Moreover, this review draws attention to the many dubious approximations, assumptions, mistakes and ambiguities that are not uncommon in this literature (Crisp, 1975). Russian investigators (Bogorov, Moiseev, Vinogradov) estimated the zooplankton biomass in the world oceans at 1.6 to 1.9 X 10 t C (as cited in De Vooys, 1979). In the FAO atlas of the living resources 

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Problems associated with excessive levels of nutrients and unwanted nuisance species have already been mentioned. There are cases in which intentional fertilization is used by aquaculturists in order to produce desirable types of natural food for the species under culture. Examples of this approach include inorganic fertilizer appHcations in ponds to promote phytoplankton and zooplankton blooms that provide food for young fish such as channel catfish, the development of algal mats through fertilization of milkfish ponds, and the use of organic fertilizers (from Hvestock and human excrement) in Chinese carp ponds to encourage the growth of phytoplankton, macrophytes, and benthic invertebrates. In the latter instance, various species of carp with different food habits are stocked to ensure that all of the types of natural foods produced as a result of fertilization are consumed. 

In cases where zooplankton are reared as a food for predatory larvae or fry, it may be necessary to maintain three cultures. Though wild zooplankton have been used successfully in some instances (eg, in Norway wild zooplankton have been collected and fed to larval Pacific haUbut), the normal process involves culturing algae to feed to zooplankton that are fed to a young shrimp or fish. 

The recent increase in the understanding of biological processes in lakes has led to the development of ecotechnical methods of manipulating the trophic status of lakes. The most widely used techniques of bio-manipulation involve artificial change in the abundance of predators to enhance grazing of phytoplankton by zooplankton. The increase in grazing pressure reduces phytoplankton densities and results in improved water transparency. 

Sensitive insects, phytoplankton and zooplankton die Whitefish and grayling die Perch and pike die Eels and brook trout die... 

Losses of crustaceans, crayfish, mayflies, and some algal and zooplankton species occur as the pH approaches 6, but most fish are largely unaffected. In the range from pH 6 to 5, major population losses are experienced. Major changes of plankton species happen while progressive loss of fish species is hkely. Fish decline is often reflected in a failure of the species to reproduce... 

Consequences of Ozone Depletion. Ozone depletion over Antarctica is causing renewed concern about the consequences of increased levels of UV reaching the earth s biosphere. One area of concern involves the free-floating microscopic plants, known collectively as phytoplankton (the grass of the sea), which through the process of photosynthesis, fix carbon dioxide into living organic matter. Phytoplankton forms the basis of the marine food chain on which zooplankton (animal plankton) and all other components of the ecosystem depend for their sustenance. 

This equation was originally proposed for "average" plankton, a category that included both zooplankton and phytoplankton. This mean elemental ratio of C/N/P = 106/16/1 by atoms is highly conserved (Falkowski et al., 1998) and reflects the average biochemical composition of marine phytoplankton and their early degradation products. 

Phytoplankton to zooplankton +3,0 Whole organism Minagawa r Wada 1984... 

Phytoplankton Zooplankton Rainbow trout smelt Lake trout Herring gull eggs... 

HPLC has also been utilized in more complex food chain transfers. It has been known for some time that the toxins can be responsible for fish kills in the Bay of Fundy 18). The vectors for these fish kills are zooplankton that feed on toxic dinoflagellates. In two related studies (79 Sullivan, unpublished), HPLC was utilized to investigate the transport of toxins from dinoflagellates to zooplankton and then to fish. The HPLC method is ideally suited for this since only very small sample sizes (ca. 100,000 dinoflagellate cells) are required. 

Zooplankton are small, often microscopic crustaceans that live in the water colunm. They are widely distributed, common, and important in pelagic food webs. Zooplankton are eaten by marty fish and by early life stages of some fish that become piscivorous as juverriles or adrrlts. Zooplankton are not eaten by httmans but are an appropriate and relevant candidate indicator because of their importance in the trophic transfer of MeHg to fish. Sampling would not significantly affect populations or assemblages of zooplankton, even in small lakes. 

FIGURE 4.2 Concentrations of MeHg (mean 1 standard error) in zooplankton from Lake 240 of the Experimental Lakes Area (northwestern Ontario, Canada), showing seasonal variation during summer and pronounced rapid increases in mean concentration after the fall overturn. (Source Michael J. Paterson, Fisheries and Oceans Canada, Winnipeg, Manitoba, unpublished data.)... 

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