EXPERIMENTS ON BENTHIC INVERTEBRATES 



In experiments with this group of organisms, a great variety of test or- 

 ganisms is used in both countries, the USSR and the USA. 



In the USSR, various species of fresh-water gammaridae are used 

 ( Gammarus pulex , G. lacustris , Pontogammarus robustoides , etc., Asollus 

 aquaticus ), of the insects - Chironomidae , most frequently Chironomus dor - 

 sal is , for which a method has been developed of year-round cultivation under 

 laboratory conditions (Konstantinov, 1958). Remaining species of the mol- 

 lusks, ephemeroptera and odonata are less frequently used. 



Experiments with gammaridae are performed over a period of approximately 

 a month, considering survival, intensity of cannibalism, growth and multi- 

 plication of the Crustacea and their feeding rates. 



Experiments with Chironomidae extend from emergency of the larvae to 

 flight of the imagoes. Survival rate of larvae, pupae and imagoes are noted 

 (Bugayeva, Puzikova, 1974). 



In experiments on other invertebrates, survival rate and growth are 

 usually noted, sometimes breeding rate as well. 



In the USA, similar groups of benthic organisms are used. One specific 

 factor is the use of several ephemeroptera ( Baetis vagans . Ephemera simi - 

 lans , Hexagema lineata ), species which are rather sensitive to toxins. How- 

 ever, differences are observed. Our experiments with Baetis sp . (species 

 not precisely defined) have shown that this form was tolerant to methylni- 

 trophos, sevin and cobalt chloride. The American species ( Baetis vagans ), 

 judging from the results of experiments, has at least moderate sensitivity 

 (experiments of Lloyd et al_., 1976). In the USA, experiments are performed 

 on the larvae of Plecoptera ( Pteronarcis californica , Acroneura pacif ica ) 

 (Sanders and Cope, 1968). Judging from the figures they present, these 

 species are moderately, possible highly sensitive to toxins. Of the Chiro- 

 nomidae, Tanytarsus is used in the USA (in the laboratory at Duluth). Ac- 

 cording to GosNIORKh, Tanytarsus is somewhat more sensitive, at least to 

 chlorophos, than is Chironomus. 



Thus, there are no basic differences in the methods used in experiments 

 on benthic organisms in the USSR and USA, and there are no great differences 

 in the relative sensitivities of the test organisms used. 



The greatest differences are observed in methods of estimation of the 

 influence of pollutants on microorganisms and on the hydrochemical mode. 



INFLUENCE OF POLLUTANTS ON AQUATIC MICROORGANISMS 



In the USSR, experiments are performed in aquaria, to which fixed con- 

 centrations of the substances studies are added (once), then the dynamics of 

 the population of microorganisms are observed (total count on membrane fil- 

 ters, population of saprophytes growing on MPA) as well as the numbers of 



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