Oyster farming
After the local oyster species collapsed in Europe in the 1960s, Pacific oysters were imported for farming in 1964, and they were introduced to Norway in 1979. The Pacific oyster is an alien species in Europe. That is, it has got here with human help. Alien species can present a threat to natural ecosystems that have developed over a long period of time, and the Pacific oyster is one such threat.
Pacific oysters in the Oslofjord
Before 2010, only a few scattered finds of Pacific oysters were recorded in the Oslofjord. The first record in Asker was made off Hvamodden on Nesøya in 2009.
Invasion of the Oslofjord
Pacific oysters need a stable water temperature of about 18 °C for a period of one or two weeks in order to become sexually mature and to spawn. Thanks to climate change, the water temperature in the Oslofjord has increased in recent years. Oysters release from 50 to 200 million eggs every time they spawn. One square metre of seabed can be home to 1,000 individual oysters. These carpet the area and displace other species.
Chosen by Franziska, museum staff (37)