10.4 Burrowing behavior in the clam Macoma balthica 

 (Olle Linden) 



Me thods : Oil-affected clams were collected at 15-20 m depth off 

 Toro about one week after the grounding of the ship. At this time large 

 quantities of oil were floating on the surface. The clams were collected 

 by a diver and brought to the laboratory in closed plastic jars. Refer- 

 ence animals were collected off the Askci laboratory in an unpolluted 

 area of similiar depth. 



After acclimatization in the laboratory for 2-3 hours, about 20 

 clams of each of three length-classes (3-4 mm, 4-9 mm, 10-15 mm) from 

 each locality were spread out over the surface of a 5 cm thick, uncon- 

 taminated sediment layer in several glass jars. The glass jars were 

 immersed in basins containing unpolluted sea water. The number of clams 

 that had buried themselves completely was counted at several time 

 intervals . 



Results and discussions . The rates of burrowing of the bivalve are 

 shown in Figure 10.4.1. On the whole the control animals showed the 

 highest burrowing rate, and all individuals had buried completely within 

 60 min. The animals from the polluted area showed a clearly decreased 

 burrowing rate. 



Affected burrowing behavior among clams under the influence of oil 

 pollution has previously been reported by Shaw et al. (1976), Linden 

 (1977) and Taylor and Karinen (1977). 



As this experiment was performed under laboratory conditions, the 

 ecological consequences of the observed effects are still unproven. 

 However, under natural conditions behavioral disturbances such as im- 

 paired burrowing will most probably, in the long run, be unfavorable for 

 this organism. Clams unable to burrow normally may have their food 

 finding affected as they are deposit feeders. Furthermore, the impor- 

 tance of burrowing behavior in the predator-prey relationship is obvious. 



The results reported here have demonstrated that the clam Macoma 

 balthica during the Tsesis oil spill may have been subjected to such 

 sublethal effects. 



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