They have arrived…


Our investigation is up and running and after some strenuous days of fieldwork along the coast of Tjärnö bay as well as submerged in the 7°C cold Swedish waters we can already confirm the presence of at least two marine alien species.


Here you see our team of specialists detecting the invasive Pacific oyster Crassostrea gigas. This oyster originally inhabits the Pacific coast of Asia and has been introduced to Sweden around 50 years ago when trying to cultivate it near Tjärnö. From there, the pacific oyster ‘escaped’ but was not observed for another 40 years. In 2007, a massive invasion along the Swedish coast began. This alien newcomer is now competing for space with the native European oyster Ostrea edulis and the well-known blue mussel Mytilus edulis and is slowly starting to replace them. To give you an idea about its danger: Our colleagues from Australia have classified the Pacific oyster as one of the ten most damaging invasive species.


Our most recent finding in the bay is the Japanese Seaweed Sargassum muticum, or for short Japweed. Back home in Japan, this seaweed likes to grow on the Pacific oyster and was introduced to Sweden in 1988 by hitch-hiking on one of the oysters. It produces air-filled bubbles that let it float on the water surface. By employing these little buoys, the Japweed takes advantage of the ocean currents and can easily invade new areas. The seaweed is growing very fast (up to 4 cm per day) and can establish dense mats covering the surface of the ocean. This prevents light reaching deeper layers of the water column and cuts off the energy supply for native plants. Such a mat can also become entangled within a boat’s propeller and be a nuisance to us humans. Our colleagues from Sweden called the establishment of Japweed one of the most dramatic changes for coastal areas in the past century. However, there is also a good side to this story: Animals like small fish and crabs can use the seaweed for shelter and protection and up to 100 different species of animals were observed in very large seaweeds. You see, it’s not possible to simply condemn all invaders as purely evil.
Be sure that we will keep you updated on our most recent findings! In the meantime, remember to keep your eyes open and pay attention to even the smallest changes around your area!

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