Since the reduced species are the most productive (highest P/B 

 ratios, Cederwall, 1977), and are the most preferred food for the local 

 fish fauna (Aneer, 1975), the change in energy flow patterns must have 

 been drastic at the most heavily impacted station. 



Before the total effect on the local ecology can be evaluated, a 

 better estimate of the heavily impacted area is needed. A sampling in 

 June 1978, near (.less than 1 km from) station 20, but in slightly shal- 

 lower water (31 instead of 32-33 m) showed an almost normal macro-and 

 meiofauna. This fact indicates that the strongly affected area may be 

 fairly small, or at least that the effect may be rather patchy in its 

 distribution (and presumably much more pronounced on sedimentation 

 bottoms than on transport or erosion bottoms). 



6.4.2.2 Pontoporeia affinis reproduction 



An increased frequency of abnormal development or non-dif ferentiatinj 

 eggs in Pontoporeia affinis seems to be a very sensitive indicator of 

 toxic substances in the aquatic environment, since Sundelin (unpublished) 

 has also found effects at very low levels of cadmium in the water (5 ppb) , 

 Nevertheless, this effect is likely to be of only minor ecological 

 importance, unless the area affected by oil is very large, since nearly 

 all Pontoporeias seem to have left or died at the most heavily impacted 

 station. 



This is an interesting example of so-called "effects monitoring" 

 (ICES, 1978). In this case it seems that when the sub-lethal effect had 

 reached a level that could be statistically demonstrated (increase of 

 non-normal eggs from about 1 to 10%) , the macrofauna community had 

 already changed so drastically, that the impact was immediately obvious 

 and beyond the need for confirmation by statistical testing. The total 

 community thus seems to have been a better integrator of environmental 

 impact than a particular physiological parameter of a single species - 

 even a highly sensitive one. This agrees with the suggestion by Mann 

 and Clark (1978) that whole systems are better indicators of oil pol- 

 lution than single species. 



120 



