were taken at Station 20 using an experimental sampler, similar in 

 principle to that of Craib (1965). This sampler rests on a tripod. It 

 slowly lowers the core tube into the bottom sediment only after the 

 tripod has come to rest on the sediment, thus decreasing the risk of 

 surface loss due to a pressure wave. These cores were sliced into 

 layers of 0-0.5 and 0.5-1 cm. 



The oxygen content of the water above the sediment was also measured 

 (Winkler titration) for the Kajak core sampler (the Asko corer contains 

 too little water). Reference values for oxygen content were taken from 

 stations I and VI (see map Fig. 6.1). 



6.2.2 Macrofauna 



6.2.2.1 Macrofauna sampling 



The macrofauna sampling followed the recommendations of the Baltic 



2 

 marine biologists (Dybern et al., 1976). A 0.1 m van Veen grab was 



used and 8-10 samples from Station 20 (except only 3 in 1972) and 3 



samples from Station 21 (except only 2 in 1977) were taken and sieved 



live through 1 x 1 mm metal mesh sieves. The animals and sieve residues 



were preserved in 4% formaldehyde solution buffered with hexamine and 



stained with Rose Bengal, to facilitate sorting. Biomass was determined 



after at least three months of preservation, as formalin wet weight, 



after careful blotting with filter paper. Each taxon and sample was 



weighed separately. 



Animals for oil analysis were collected using either a van Veen 



grab or an Ockelmann dredge (Ockelmann, 1964) with a mesh size of 450 |Jm, 



as were the Pontoporiea affinis females used for estimating frequency of 



abnormal eggs. Animals for oil analysis were stored in hexane-cleaned 



glass bottles or aluminum foil and kept deep-frozen until analyzed. 



6.2.2.2 Reproduction of Pontoporela affinis 



The spill occurred just before the normal copulation period for 

 Pontoporeia affinis and P. femorata. Egg-bearing females of the dom- 

 inant species P. affinis were collected on 17 February and 9 March 1978 

 at the most strongly impacted of the initially sampled stations (No. 20, 

 see map, Fig. 6.1) and at an unaffected reference site (No. 15). 



100 



