CHAPTER 7: IMPACT OF OIL ON THE LITTORAL ECOSYSTEM 



I Introduction 



(Mats Notini ) 



When an oil spill occurs in coastal regions, littoral communities 

 are often severely damaged (Southward and Southward, 1978; North et al., 

 1965; Blumer et al., 1971). However, as Michael pointed out in 1977, 

 more studies of long-term and low-level effects of oils on basic com- 

 munity processes are needed. The degree and duration of the injuries 

 vary depending on the quantity and quality of the oil reaching the shore 

 line. The clean-up techniques employed when removing the oil may also 

 significantly affect duration and degree of damage. 



The residence time of the oil in the littoral system is dependent 

 on the energy input in the area and mechanical energy (e.g., wind and 

 wave action, presence of ice) is the single most important factor 

 (Owens, 1978). 



The Tsesis ran aground in shallow, narrow waters and large amounts 

 of the oil could not be prevented from reaching the nearby shores during 

 the first hours and days after the accident. Therefore, extensive 

 effects on the littoral communities could be predicted. 



On the second day following the accident (October 27), quantitative 

 "pre-spill" sampling of the Fucus fauna was made at four as yet unaf- 

 fected stations (Section 7.2). Three of these stations were later hit 

 by the oil spill. Sampling and studies of the effects of the oil on 

 these stations and three complementary stations were repeated at inter- 

 vals during the first year following the spill. 



Another type of study carried out in the littoral zone at the same 

 seven stations is reported in section 7.3. Here, the fauna and flora of 

 the typical vegetation belts (i.e. Ceramium, Fucus and red algal belts) 

 and Mytilus belts along the bottom slope were sampled according to the 

 technique described by Dybern et al. (1976). With this method not only 

 the plants themselves but also the animals dwelling in the algae and 

 those living on the bottom below are sampled. This sampling was carried 

 out in November 197-7 and June 1978. 



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