6.4.3 Meiofauna 



The meiofauna material suffers from lack of pre-spill data from 

 station 20 (pre-spill samples are available but have not yet been sorted) 

 All post-spill cores collected at station 20 are exceptionally low in 

 both ostracods (Fig. 6.11) and other non-nematode meiofauna (Fig. 6.12), 

 when compared both to station 15 and 8 other mud stations in the 25-45 m 

 depth range (taken from a survey of the Askb'-Landsort area by Ankar and 

 Elmgren, 1976; Fig. 6.14). Pre-spill macrofauna data shows station 20 

 to be a rather normal station (except for a trend of increasing biomass 

 of Macoma balthica, due to eutrophication) , and there is thus no reason 

 to expect it to have harbored an aberrant meiofauna. This would suggest 

 that the extremely low post-spill meiofauna values are a direct oil 

 effect. For the ostracods, with their protective shells, it is also 

 possible that some recently dead animals were counted as live (since the 

 samples were counted after preservation) . 



The dredge samples of large ostracods taken in February and March 

 show a much higher proportion of live ostracods at the reference station 

 15 than at the spill station 20, where only few live large ostracods 

 were found (Fig. 6.13). This is not directly comparable to the results 

 from the meiofauna cores (where a 40 pm sieve was used) since only the 

 largest ostracods were included, (0.5 mm screen), but it represents a 

 much larger sample, and is therefore probably more reliable. There is 

 thus some evidence of a high mortality of ostracods and other non- 

 nematode meiofauna following the spill, but not enough to be entirely 

 conclusive. The ostracod species concerned, and most of the other 

 meiofauna, lack swimming ability, and could not have emigrated from the 

 area . 



The continued low abundance of all meiofauna except nematodes, for 

 10 months following the spill, also indicates the low post-spill pop- 

 ulations to be an oil effect, since a great development of the meiofauna 

 would normally have been expected after the reduction of the competing 

 macrofauna. For most of this period oxygen conditions were good, and 

 contributed no alternative explanations for the low non-nematode meio- 

 fauna at station 20. 



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