7.3 Effects on the phytal ecosystem 

 (H. Kautsky) 



7.3.1 Materials and Methods 



Seven stations were chosen to represent the entire area contam- 

 inated by the oil spill (Fig. 7.2.1). Most stations were placed in 

 coves as it was expected that these would hold the oil for a longer time 

 and the pollution effect would be higher and easier to detect. In some 

 cases the oil was, in fact, forced into the coves with the help of 

 spill-booms. All seven stations, including a reference station (G) with 

 no visible oil spill, were sampled in November 1977 and resampled in 

 June 1978. From the June sampling only 3 stations have been sorted (B, D 

 and G) . 



Sampling was done by SCUBA divers, using the technique described in 

 Dybern et al. (1976) and by Jansson and Kautsky (1977). The vegetation 

 coverage and the Mytilus edulis coverage were estimated visually. The 

 vertical extent of each identified belt was noted. Within each zone, 

 quantitative samples were taken at random. In November, the sampling 

 sites were marked with bricks; in June, random sampling was made in the 

 vicinity of these bricks in order to facilitate comparison between 

 November and June samples. Square frames with a side of 15, 20 or 50 cm 

 were used depending on the kind of vegetation dominant in each belt. 

 The samples in November were sorted and dried shortly after collection; 

 in June the samples were frozen and sorted later. 



The samples were analyzed for species composition, abundance and 



1S£ 



2 



2 

 biomass. The results are given in individuals per m or in g dry weight 



per m' 



7.3.2 Results 



7.3.2.1 Field observations 



November: At the most contaminated stations B, C and D (see Fig. 

 7.3.1) no free-swimming animals could be observed. At location B an oil 

 smear was identified on Mytilus edulis down to a depth of 4 m. 



146 



