Our Liviiii; Ri'sniirits — Aquanr F.ccsystcms 



:?.5.? 



Environmental Quality 

 Indicators 



Pe)lluted waters often hu\e a rich and cliai- 

 acteristic protozoan fauna. The relative abun- 

 dance and diversity of proto/oa are used as indi- 

 cators of organic and toxic pollution (Cairns el 

 al. 1972; Foissner 1987: Niederlehner et al. 

 1990; Curds 1992). Bick (1972), for example, 

 provided a guide to ciliates that are useful as 

 indicators of environmental quality of European 

 freshwater systems, along with their ecological 

 distribution with respect to parameters such as 

 amount of organic material and oxygen levels. 

 Foissner (1988) clarified the taxonomy of 

 European ciliates as part of a system for classi- 

 fying the state of aquatic habitats according to 

 their faunas. 



Symbiotic Protozoa 



Parasites 



Protozoa are infamous for their role in caus- 

 ing disease, and parasitic species are among the 

 best-known protozoa. Nevertheless, our know 1- 

 edge has large gaps, especially of normally free- 

 living protozoa that may become pathogenic in 

 immuno-compromised individuals. For exam- 

 ple, microsporidia comprise a unique group of 

 obligate, intracellular parasitic protozoa. 

 Microsporidia are amazingly diverse organisms 

 with more than 700 species and 80 genera that 

 are capable of infecting a variety of plant, ani- 

 mal, and even other protist hosts. They are 

 found worldwide and have the ability to thrive 

 in many ecological conditions. Until the past 

 few years, their ubiquity did not cause a threat 

 to human health, and few systematists worked 

 to describe and classify the species. Since 1985, 

 however, physicians have documented an 

 unusual rise in worldwide infections in AIDS 

 patients caused by four different genera of 

 microsporidia (Encephalitozoon. Nosema. 

 Pleistophorci. and Eniewcytozoon). According 

 to the Centers for Disease Control in the United 

 States, difficulties in identifying microsporidian 

 species are impeding diagnosis and effective 

 treatment of AIDS patients. 



Protozoan Reservoirs of Disease 



The presence of bacteria in the cytoplasm of 

 protozoa is well known whereas that of viruses 

 is less frequently reported. Most of these reports 

 simply record the presence of bacteria or virus- 

 es and assume some sort of symbiotic relation- 

 ship between them and the protozoa. Recently, 

 however, certain human pathogens were shown 

 to not only survive but also to multiply in the 

 cytoplasm of free-living, nonpathogenic proto- 



zoa. Indeed, it is now believed that protozoa are 

 the natural habitat for certain pathogenic bacte- 

 ria. To date, the main focus of attention has been 

 on the bacterium Legionella pneumophila, the 

 causative organism of Legionnaires' disease; 

 these bacteria live and reproduce in the cyto- 

 plasm of some free-livint; amoebae (Curds 

 1992). 



Symbionts 



Some protozoa are harmless or even benefi- 

 cial symbionts. A bewildering array of ciliates, 

 for example, inhabit the rumen and reticulum of 

 ruminates and the cecum and colon of equids. 

 Little is known about the relationship of the cil- 

 iates to their host, but a few may aid the animal 

 in digesting cellulose. 



Data on Protozoa 



Bibliography 



While our knowledge of recent and fossil 

 foraminifera in the U.S. coastal waterways is 

 systematically growing, other free-living proto- 

 zoa are poorly known. There are some regional 

 guides and, while some are excellent, many are 

 limited in scope, vague on specifics, or difficult 

 to use. Largely because of these problems, most 

 ecologists who include protozoa in their studies 

 of aquatic habitats do not identify them, even if 

 they do count and measure them for biomass 

 estimates (Taylor and Sanders 1991 ). 



Parasitic protozoa of humans, domestic ani- 

 mals, and wildlife are better known although no 

 attempt has been made to compile this informa- 

 tion into a single source. Large gaps in our 

 knowledge exist, especially for haemogre- 

 garines. microsporidians. and myxosporidians 

 "{see Kreier and Baker 1987). 



Museum Specimens 



For many plant and animal taxa, museums 

 represent a massive information resource. This 

 is not true for protozoa. In the United States, 

 only the National Natural History Museum 

 (Smithsonian Institution) has a reference collec- 

 tion preserved on microscope slides, but it does 

 not have a protozoologist curator and cannot 

 provide species" identification or verification 

 services. The American Type Culture Collection 

 has some protozoa in culture, but its collection 

 includes relatively few kinds of protozoa. 



Ecological Role of Protozoa 



Although protozoa are frequently over- 

 looked, they play an important role in many 

 communities where they occupy a range of 

 trophic levels. As predators upon unicellular or 



