Ecomare

Every year, the fisheries department of IMARES takes stock of the wild oyster banks situated in the Grevelingen. Up till 1995, there was always talk of a large death rate due to the disease caused by the protozoan, Bonamia ostreae. This disease appeared in the beginning of the 1980s in the oyster stock in the Oosterschelde and eventually destroyed most of the oysters in the Grevelingen later on. The disease was probably imported along with oysters from Brittany, which in turn were infected by imports from California.
In 1996 and 1997, the death rate due to Bonamia ostrea appeared much less than in previous years. A different disease broke out in May 1996, whereby even more oysters died. This time, the flowering of the harmful algae Hexabita was most likely the cause. In 1998, the disease caused by Bonamia ostrea appeared 3.5 times more often than in 1997. The RIVO assumes that there is a link between the water temperature and the appearance of the virus. Mild winters seem to be followed by a year with much disease. The fisheries department of IMARES does not yet have any solution for the disease.