The Bassin d’Arcachon, on the southwest Atlantic coast of France, is an important oyster-rearing area. From 1976 to 1981, the oyster industry was disturbed by shell abnormalities and by a drastic reduction of reproduction. As a consequence, the number of oyster farmers declined by 50%. The phenomena were consequent to a large increase in pleasure-craft activities in the bay; tributyltin compounds released from antifouling paints were suspected as the main cause of these abnormalities. The failure of larvae to survive the D larval stage was assessed experimentally by using the Crassostrea gigas embryolarval bioassay. At first, it was established experimentally that the use of tributyltin compounds was dangerous in oyster-farming areas. Above 1 µg l-1 tributyltin (TBT) acetate, fertilized eggs cannot develop to the D larval stage; at 1 (µg l-1 the D larval stage is reached, but all larvae are abnormal and die within a few days; from 0.5 to 0.05 µg l-1 abnormalities and mortalities are still considerable (>78% over a 12-d period), and larval growth is strongly affected. At 0.02 µg practically no action is observed, and this value seems to represent the threshold tolerance level of the larvae. On the other hand, neither low nor varying temperature could explain the lack of larval growth observed in the field; the failure in larval development could not be attributed to the action of TBT on the gamete viability from Arcachon adult oysters, or to its direct action on embryos and larvae. In 1981, D larvae isolated from the plankton of the Bassin d’Arcachon were reared in the laboratory, in seawater collected at the same place and time as the larvae. In the field, the stomach of the larvae remained uncolored (absence of food), and the larvae did not reach the early umbo stage; in the laboratory, larvae of the same brood stock fed normally (stomach well colored), and reached the early umbo and the umbo stage 12 d after the beginning of the experiments. From this it was supposed that D larvae in the field could not find the appropriate food required during the first days of their pelagic life; this was probably due to a disturbance in the development of the nanoplankton caused by the action of antifouling paints containing organotin compounds. Since the ban on TBT-based antifouling paints was put into effect in 1982, the Japanese oyster has reproduced on a commercial scale every year in the Bassin d’Arcachon.
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- Embryogenesis and Larval Development in Crassostrea Gigas: Experimental Data and Field Observations on the Effect of Tributyltin Compounds
- Springer Netherlands
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