bivalve Macoma balthica (Fig. 6.7) which showed no decline. The same 

 was true of the priapulid Halicryptus spinulosus (Fig. 6.8), which is 

 the last of the five macro fa una species normally found at these stations. 



Station 20 was sampled again in February and August 1978. The 

 February sampling showed slightly higher abundance of amphipods and 

 Harmothoe but instead, a decrease in Macoma and Halicryptus . In August, 

 amphipods and Harmothoe were once again virtually absent while Macoma 

 and Halicryptus now showed an increase. These small variations are 

 statistically significant for both Pontoporeia spp. as well as for 

 Macoma and Harmothoe (p < 0.005, Rank-sum test for several samples- 

 namely November 1977, February and August 1978, Dixon and Massey, 

 1967:345), but not for Halicryptus . 



Station 21 was revisited in June 1978. This time all species 

 showed abundance values which differed little from what had been normal 

 during November in earlier years (Figs. 6.3-6.8). 



6.3.2.2 Pontoporeia affinis reproduction 



In spite of the drastic reduction in Pontoporeia affinis population 

 density at Station 20, it was possible to collect a small number of 

 gravid females for determinations of egg numbers and frequency of non- 

 developing embryos (Figs. 6.9a-b). The total percentage of abnormal plus 

 undifferentiated embryos was about 10°/o at Station 20, but only about 1% 

 at reference station 15, far from the oil spill (Table 6.1). This 

 difference is statistically significant (p < 0.05) using a normal 

 approximation to a rank-sum test, that combines the information from 

 both sampling occasions (Lehman, 1975:5-23 and 132-141). 



6.3.3 Meiofauna 



Meiofauna samples were sorted from Station 20 in November 1977 and 

 February, March, August and September 1978 and from Station 21 in Novem- 

 ber 1976 (one year before the spill). Since the macrofauna at station 21 

 seemed to show some influence from the spill, another reference station 

 was selected for the meiofauna. Station 15, at a depth of 41-44 m, was 

 selected as most representative, even though it is about 10 m deeper 



110 



