2 Effects on the supralittoral fauna 

 (Maria Foberg) 



2.1 Introduction 



The importance of having knowledge on the effects of an oil spill, 

 not only in the water but also on the adjacent areas above the water- 

 line, is quite obvious since few investigations have been carried out 

 for this purpose, especially in the Baltic Sea. In order to obtain 

 comparable samples the wrack bed was chosen as a sampling area as it was 

 a biotope which occurred at several of the stations. 



8.2.2 Materials and methods 



Three supralittoral stations situated close to stations B, C and D 

 and one close to the reference station G (Fig. 7.2.1) were investigated 

 during the first two weeks of August 1978, over nine months after the 

 spill. On two occasions - August 2 and August 8 - six pit-fall traps 

 containing water and detergent (used for decreasing the surface tension) 

 were placed in the wrack bed at each station for 24 hours. At the same 

 time two quantitative samples were randomly taken at each station with a 

 frame (20 x 20 cm) so that 10-15 mm of the upper part of the ground 

 material was included in the sample - making a total of 12 traps (10 at 

 station G since two were lost) and 4 quantitative samples from each 

 station. 



The samples were sorted (the quantitative first by hand and then 

 with a Tullgren apparatus, as described in Backlund, 1945), determined 

 to taxonomic group (family), in some cases to species, and counted. In 

 those cases where a large number of spring-tails (Collembola) were found 

 it was not possible to determine every individual. Instead a subsample 

 was examined and the systematic groups recorded. A comparison between 

 number of individuals and number of systematic groups at the different 

 stations was made (Tables 8.2.1, 8.2.2). 



The number of individuals in the quantitative samples was recalcu- 

 lated to 100 g wrack dry weight. All newly hatched isopods, which were 

 presumably caught while still clinging to their mother, were left out of 

 the calculations, but the numbers are given in Table 8.2.3 (and later 

 in Table 8.2.6) . 



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