254 



Aquatic Ecosystems — Our Liviiit; Resources 



For further information: 



Diana Lipscomb 



George Washington University 



Department of Biological Sciences 



Washinaton, DC 20052 



filamentous algae, bacteria, and inicmftingi. 

 protozoa play a role both as herbivores and as 

 consumers in the decomposer link of the food 

 chain. As components of the micro- and meio- 

 fauna, protozoa are an important food source 

 for microinvertebrates. Thus, the ecological role 

 of protozoa in the transfer of bacterial and algal 

 production to successive trophic levels is impor- 

 tant. 



Factors Affecting Growth and Distribution 



Most free-living protozoa reproduce by cell 

 division (exchange of genetic material is a sep- 

 arate process and is not involved in reproduc- 

 tion in protozoa). The relative importance for 

 population growth of biotic versus chemical- 

 physical components of the environment is dif- 

 ficult to ascertain froin the existing survey data. 

 Protozoa are found living actively in nutrient- 

 poor to organically rich waters and in fresh 

 water varyfng between ()°C (32°F) and 5()°C 

 (122°F). Nonetheless, it appears that rates of 

 population growth increase when food is not 

 constrained and temperature is increased (Lee 

 and Fenchel 1972; Fenchel 1974: Montagnes et 

 al. 1988). 



Comparisons of oxygen consumption in var- 

 ious taxonomic groups show wide variation 

 (Laybourn and Finlay 1976). with some aerobic 

 forms able to function at extremely low oxygen 

 tensions and to thereby avoid competition and 

 predation. Many parasitic and a few free-living 

 species are obligatory anaerobes (grow without 

 atmospheric oxygen). Of the free-living forms, 

 the best known are the plagiopylid ciliates that 

 live in the anaerobic sulfide-rich sediments of 

 marine wetlands (Fenchel et al. 1977). The 

 importance of plagiopylids in recycling nutri- 

 ents to aerobic zones of wetlands is potentially 

 great. 



Ecological Interactions 



Because of the small size of protozoa, their 

 short generation time, and (for some species) 

 ease of maintaining them in the laboratory, 

 ecologists have used protozoan populations and 

 communities to investigate competition and 

 predation. The result has been an extensive lit- 

 erature on a few species studied primarily under 

 laboratory conditions. Few studies have been 

 extended to natural habitats with the result that 

 we know relatively little about most protozoa 

 and their roles in natural communities. 

 Intraspecific competition for common resources 



often results in cannibalism, sometimes with 

 dramatic changes in morphology of the canni- 

 bals (Giese 1973). Field studies of interspecific 

 competition are few and most evidence for such 

 species interactions is indirect (Cairns and 

 Yongue 1977). 



References 



Bick. H. 1972. Ciliated protozoa. An illustrated guide to the 

 .species used as biological indicators in freshwater biolo- 

 gy. World Health Organization, Geneva. 198 pp. 



Cairns. J.. G.R. Lanza, and B.C. Parker 1972. Pollution 

 related structural and functional changes in aquatic com- 

 munities with emphasis on freshwater algae and proto- 

 zoa. Proceedings of the National Academy of Sciences 

 124:79-127. 



Cairns, J., and J. A. Rulhven. 1972. A test of the cosmopoli- 

 tan distribution of fresh-water protozoans. Hydrobiologia 

 39:405-427. 



Cairns, J., and W.H. Yongue. 1977. Factors affecting the 

 number of species of freshwater protozoan communities. 

 Pages 257-.303 in J. Cairns, ed. Aquatic microbial com- 

 munities. Garland, New York. 



Curds, C.R. 1992. Protozoa and the water industry. 

 Cambridge University Press, MA. 122 pp. 



Fenchel. T. 1974. Intrinsic rate increase: the relationship 

 with body size. Oecologia 14:,317-.'?26. 



Fenchel. T, T, Perry, and A. Thane. 1977. Anaerobiosis and 

 symbiosis with bacteria in free-living ciliates. Journal of 

 Protozoology 24:154-163. 



Foissner. W. 1987. Soil protozoa: fundamental problems, 

 ecological significance, adaptations in ciliates and tes- 

 taceans, bioindicators. and guide to the literature. 

 Progress in Protistology 2:69-212. 



Foissner. W. 1988. Ta.xonomic and nomenclatural revision 

 of Stadecek's list of ciliates (Protozoa: Ciliophora) as 

 indicators of water quality. Hydrobiologia 166:1-64. 



Giese. A.C. 1973. Blepluirisimi. Stanford University Press, 

 CA. 366 pp. 



Kreier. J. P. and J.R. Baker. 1987. Parasitic protozoa. Allen 

 and L'nwin. Boston, MA. 241 pp. 



Laybourn, J., and B.J. Finlay. 1976. Respiratory energy 

 losses related to cell weight and temperature in cihated 

 protozoa. Oecologia -14: 165-174. 



Lee. C.C., and T. Fenchel. 1972. Studies on ciliates associ- 

 ated with sea ice from Antarctica. II. Temperature 

 responses and tolerances in ciliates from Antarctica, tem- 

 perate and tropical habitats. Archive fUr Protistenkunde 

 114:237-244. 



Montagnes, D.J.S., D.H. Lynn. J.C. Roff. and WD. Taylor. 

 1988. The annual cycle of heterotrophic planktonic cili- 

 ates in the waters surrounding the Isles of Shoals. Gulf of 

 Maine: an assessment of their trophic role. Marine 

 Biology 99:21-30. 



Niederlehner, B.R., K.W. Pontasch. J.R. Pratt, and J, Cairns. 

 1990. Field evaluation of predictions of environmental 

 effects from multispecies microcosm to.vicity test. 

 Archives of Environmental Contamination and 

 Toxicology 19:62-71. 



Taylor, W., and R. Sanders. 1991. Protozoa. Pages 37-93 in 

 J.H. Thorp and A. P. Covich, eds. Ecology and classifica- 

 tion of North American freshwater invertebrates. 

 Academic Press, New York. 



