of the oxygen analyses are given in Fig. 6.2. The few bottom water 

 oxygen analyses made at station 20 do not deviate markedly from measure- 

 ments made at closer intervals at reference station VI and station I 

 farther into the "Himmerf jard" . That the bottom water values are slight- 

 ly lower is only natural, since the other analyses were made on samples 

 taken farther from the bottom (an ordinary water sampler, not a corer 

 was used) . 



6.3.2 Macrofauna 



6.3.2.1 Macrofauna community response 



Two stations were followed in detail (Stations 20 and 21, shown in 

 map, Fig. 6.1). Results are given in Figs. 6.3-6.8. 



As can be seen in Figs. 6.3 and 6.7 the effects of the oil spill 

 have to be evaluated against a background of gradual change during 

 1972-77 due to eutrophication caused by the "Himmerf jard" sewage plant. 

 The most important component of this change is a gradual increase in 

 abundance and biomass of Macoma balthica at both stations, most clearly 

 marked at Station 20 (see Fig. 6.7). This trend is even stronger far- 

 ther up the "Himmerf jard" closer to the sewage plant (Larsson, pers. 

 comm. ) . 



The November 1977 sampling, carried out 16 days after the start of 

 the spill, showed a dramatic and statistically significant reduction in 

 total macrofauna abundance at station 20 (Fig. 6.3). On this occasion a 

 smell of oil was noticed from several of the grab samples. At Station 

 21 also, the abundance was lower than during any of four preceding 

 years, but this difference was difficult to test statistically due to 

 the lower number of samples taken at this station. The reduction was 

 mostly due to an almost total disappearance of Pontoporeia af finis and 

 P. femorata and the polychaete Harmothoe sarsi from Station 20 (Figs. 

 6.4, 6.5 and 6.6). All these decreases are statistically significant 

 (p < 0.001 when November 1976 and November 1977 are compared, Rank-sum 

 test according to Dixon and Massey, 1969:344). The amphipods (but not 

 the polychaete) were also reduced at Station 21, but far less drastically. 

 The total macrofauna biomass at both stations was dominated by the 



102 



