4.3.4.1 Field Studies 



Abnormal growth effects were first noticed in the Pacific Oyster 

 Crassostrea qiqas in France. The Pacific oyster was introduced into 

 France for oyster farming in 1968, to replace naturally declining locally 

 farmed oysters. In France, growth anomalies in the development of (L. 

 qiqas larvae were first observed in 1976 in a small area of Arcachon Bay. 

 By 1977, these anomalies were detected in the rest of the Bay. The most 

 obvious growth abnormality was the malformation of the valves, 

 particularly the upper one (a balling effect) . Early researchers noticed 

 that there was a correlation between the number of marinas or boat 

 moorings and the occurrence of the shell malformations (Alzieu, 1986) . 

 A stronger correlation was suggested when this tendency for shell 

 thickening could be reversed by moving the oysters to an area far removed 

 from boating activity. Also there were other problems than just growth 

 and shell deformation, some regions have little or no natural spat 

 (settling oyster larval stage) fall, suggesting toxic effects to early 

 oyster life stages. However, these biological field observations did not 

 have supporting water column chemistry (TBT concentration data) for the 

 waters of the local areas where the shell deformalities were found, making 

 these correlations interesting but not convincing. 



Similar observations were subsequently made on oysters from England 

 collected from the Rivers Crouch and Roach, by Waldock and Miller (1983) , 

 Waldock et al. (1983, 1987). The Pacific oyster is far more sensitive to 

 the toxicity of TBT than the European flat oyster ( Ostrea edulis ) . Oyster 

 farming of C± Giqas was attempted and was quite unsuccessful in many areas 

 of the U.K. , particularly the estuaries of the Rivers Crouch and Roach on 

 the east coast of England, which are two of the most highly TBT 

 contaminated waters in the U.K. (Thain, 1986) . 



The mechanisms of formation of shell anomalies in the growth and develop- 

 ment of oysters has been studied by French and British scientists and they 

 have found the development of a series of chambers in the shell which are 

 formed as the layers of calcification are laid down within the shell. 

 These chambers are filled with a jelly-like protein (see Figure 4.1, from 

 Waldock and Thain, 1983) . Analysis of the protein in this substance has 

 shown a higher proportion of threonine and a smaller amount of serine, 

 glycine, and aspartic acid compared to the usual composition of the normal 

 calcification proteins. The components of this jelly-like substance does 

 not appear to bind with the Ca +2 or with HCO 3 , on the exposed surface 

 of the shell and when added to a solution of CaC0 3 TBT slows down or 

 prevents the formation of crystals of CaCO-j. This suggests that the 

 formation of this gelatinous substance on the inside surface of the 

 oysters shell is an abnormal process which is the result of a perturbation 

 of molecular genetic mechanisms (Alzieu, 1986) . In the most acute 

 malformations in Arcachon Bay, France, the thickening of the oyster shell 



IV--16 



