June: The sulphur bacterium Beggiatoa , which is an indicator of 

 reduced bottoms, is not uncommon in the area, especially in depressions 

 with stagnant water, often at the bottom of the littoral slope. At the 

 oil polluted stations, Beggiatoa covered greater than normal areas even 

 on flat bottoms in June 1978. A higher frequency of Mysidae could be 

 observed at the reference station G and around the Asko Laboratory 

 (adjacent area) than at contaminated stations. A peculiar growth of the 

 tips of Fucus vesiculosus was also observed at station B and in lower 

 frequency at Station C. It looked as if young plants had settled on the 

 old degraded plant tips. On the shore at station B, a beach clean-up 

 was carried out in June, causing a light oil film on the surface water. 

 Samples taken on the deep Mytilus bottoms (8 m depth) visibly contained 

 oil. The Cladophora belt was a bit broader in June, probably due to low 

 water during spring. 



7.3.2.2 Calculations from collected data 



November: A summary of biomass and frequency of dominating animal 

 groups in the Cladophora and Fucus belt in November is made in Table 

 7.3.1. In some vegetation belts at the most contaminated stations, 

 animal species groups, common at the reference station, were absent 

 (Table 7.3.2). The frequency of vagile (and semisessile) forms was very 

 low at stations B, C, D, E and F, probably as a direct response to oil 

 contamination. The mussel Mytilus edulis dominated the biomass in the 

 entire area. At the reference Station G about 20% of the total biomass 

 in the Fucus belt consisted of other species. The vagile forms con- 

 tributed only a few per cent. In the Cladophora belt about 40% of the 

 total animal biomass consisted of vagile forms. At all other stations 

 Mytilus together with Balanus improvisus dominated the fauna biomass 

 totally, particularly at stations B and F. The vagile forms played a 

 minor part. 



June and comparisons with November: The dominating plant species 

 from three vegetation belts are listed in Table 7.3.3. Only five spe- 

 cies dominated the biomasses in the specific zones. Cladophora glomerata 

 replaced Ceramium tenuicorne in the shallowest zone (C), and Pilayella 



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