The third type of study carried out in the littoral zone concerned 

 in situ measurements of community metabolism according to the method 

 described by Guterstam, 1977 (Section 7.4). This investigation was 

 carried out during the acute phase of the accident. 



7.2 Effects on Fucus macrofauna 

 (Mats Notini) 



7.2.1 Introd uction 



The extensive archipelagos of the Baltic cover about 6% of its 

 surface area. The bladder wrack Fucus vesiculosus is the dominating 

 seaweed of the archipelagos all around the Baltic. 



There is no question as to the central role played by this alga in 

 the ecological system of the Baltic sea. The net production of the 

 bladder wrack in the area of Asko has been estimated for September to be 

 about 20% of the entire plant plankton production. The annual produc- 

 tion of the seaweed is probably higher, since macroalgae grow also when 

 the plankton biomass is low (Guterstam, 1977). It has a maximum density 

 at a depth between 0.5 and 2 m. This zone contains a great variety of 

 ecological niches and is probably the most diverse and productive habi- 

 tat in Baltic shallow waters (Jansson and Wulff, 1977). More than 70% 

 of the macroorganisms of the Baltic sea occur at one time or another in 

 this belt (Haage, 1969). The food chains of about 50 species of fish 

 and 40 species of birds run through this area (Jansson, 1974). 



In the enclosed Baltic sea and its extensive archipelagos the 

 diverse ecosystem of the Fucus belt is never far away. Therefore, any 

 major oil spill in this area will reach this system within hours or at 

 the most a few days. A recent study indicated drastic and long-term 

 effects of an oil spill in this system (Notini, 1978). Almost the 

 entire fauna belonging to the Fucus zone was wiped out and recruitment 

 was found to take several years. This spill occurred at the same season 

 of the year (October 1970) about 30 km northeast of the Tsesis grounding. 



130 



