Hoe gevaarlijk is de Japanse oester? Over ecologische effecten van een geïntroduceerde oester op inheemse schelpdieren

In the last couple of years, the introduced Pacific oyster Crassostrea gigas (Thunberg) has regularly appeared in the the newspapers, most of the time in a negative way. It has even been nicknamed the ‘Pitbull oyster’. But really how dangerous is this species ? The Pacific oyster has many similarities with native bivalves. It feeds in the same manner and has roughly the same life cycle. There are, however, differences that may cause trouble in the future. The Pacific oyster forms persistent reef structures that locally hamper colonization of burrowing bivalves such as the cockle Cerastoderma edule. Reef formation is accelerated due to gregarious settlement of the larvae. Furthermore, Pacific oyster larvae swim faster than the larvae of native bivalves, such as the mussel Mytilus edulis. The oyster larvae are also able to avoid filtration by adult bivalves. They do not react to hydromechanical stimuli in inhalant feeding current flow fields of adult bivalves, but they respond to the presence of an adult bivalve by redistributing to higher water levels. Mussels do not show this behaviour, and were filtered twice as much as oyster larvae in still water in a laboratory set-up. In conclusion, the Pacific oyster is not a monster, but it could cause some problems in future. Not only because of the features mentioned above, but also because the Pacific oyster is hardly eaten by predators such as estuarine birds.