Station 3 



0.1 1 5 10 



Benzo(a)pyrene Concentrations (pg/i) 



100 



50- 



^N 

 — V- 



Station 45 



0.1 1 5 10 



Benzo|a)pyrene Concentrations (|ig/l) 



100- 



50- 



Station 7 



0.1 1 5 



Benzo(a)pyrene Concentrations (jag/l) 



10 



100 



50- 



Station 9 



Benzo(a)pyrene Concentrations (pg/1) 

 Fig. 6. Negative effects of BaP concentrations on primary production (P) 

 and total number of infusoria (N) on Stations 3, 7, and 9. 



phytoplankton and microzooplankton to toxicants varied over 

 a range of about one order of magnitude for all values 

 (Table?). 



Concerning the PCB's additions, it should be noted that 

 the highest toxicity on the phytoplankton community was 

 found on Stations 3 and 7, and for microzooplankton on 

 Stations 18 and 41 (Figs. 4,5). The average critical 

 concentrations of PCB's for phyto- and microzooplankton in 

 the Bering Sea ecosystem were 30 |ag/l and 1 1 |ig/l, respectively 

 (Table 7). The strongest PCB's toxic effects on bacterial 

 production were found at Stations 3 and 4, and critical 

 concentrations to the bacterioplankton community were about 

 50 )ag/l (Table 3). It was very surprising that on Station 35, 

 additions of Cu, Cd, and BaP had a very strong negative effect, 

 but toxic amounts of PCB's additions showed that values of 

 bacterial production were stimulated (Tables 3 and 4). The 

 PCB ' s critical concentrations for the whole plankton community 

 calculated for Station 3 were about 5 |ig/l (Table 5 ). The critical 

 concentrations data obtained in the Chukchi Sea ecosystem 

 showed that values of critical concentration of BaP (target 



Station 53 



Fig. 



Benzo(a)pyrene Concentrations (pg/1) 



7. Negativeeffactsof BaP concentrations on primary production (P) and 

 total number of infusonia (N) on Stations 45 and 53. 



primary production and microzooplankton) were significantly 

 less than in the Bering Sea ecosystem (Tables 7,8). At the same 

 time, the effects of heavy metals and PCB's on primary 

 production in the Bering Sea were slightly stronger than in the 

 Chukchi Sea ecosystem (Tables 7.8). 



The critical concentration of BaP and PCB's on infusoria 

 of the Chukchi Sea was three and two times lower than the 

 Bering Sea, while the effects of Cu and Cd were slightly higher 

 (Tables 7,8). 



The above mentioned differences in the sensitivity of 

 plankton communities can be ascribed to the difference in 

 adaptation of these communities to the pollutants and also to 

 their species composition. It should be noted that the temperature 

 of the water in the Chukchi Sea during our studies was about 

 5°C lower than that in the Bering Sea. For this reason, the 

 comparative resistance of the plankton communities of the 

 Chukchi Sea to the toxic contaminants would be even less than 

 was determined in the course of these ecotoxicological 

 experiments (Oduni, 1975; Izrael & Tsyban, 1989). 



Discussion 



The values of critical concentrations of the pollutants 

 obtained in our experiments of 1984 and 1988 show that the 

 resistance of the plankton community of the Bering Sea for the 

 summer period were similar for Cu and Cd ( Liftshits & Korsak, 

 1988; Izrael & Tsyban, 1989). In addition. Station 35 near 

 St. Lawrence Island, which had the highest levels of primary 

 production, was the most sensitive to all toxic contaminant 

 additions, both in 1984 and 1988. Further study is needed to 



360 



