The Nature Conservancy

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Marine Invasives

The European green crab, a voracious predator of shellfish and small crustaceans, dominates the habitats it invades. This crab invades quickly and can outcompete native crabs and birds for food. It also causes declines in ecologically and commercially important species, including causing the collapse of the soft-shell clam fishery in Maine. © Andrew Cohen, SFEI,

Caulerpa is a tropical seaweed that has wreaked havoc in the Mediterranean and in Australia. Once established, it is quickly transported on the anchors of fishing and recreational boats. It overgrows native seagrass and is toxic to many fish. When a population was discovered in a California harbor in 2000, reactions were rapid. Six years and over $4 million later, teams of divers succeeded in eradicating this invader. Early detection in the new habitat and information on the impacts of this species were key in the fast and effective response, preventing larger damages and costs. © Alexander Meinesz,

Prized for their plump meat, Pacific oysters have been transported from Japan to be farmed in coastal waters around the world since the early 1900s. They can aggressively invade surrounding habitats, attaching their large shells to rocks in dense groupings in the intertidal zone and squeezing out native oysters and other species. Other invasive species and pathogens can ride on their shells, bringing further harm to ecosystems and local economies. © Stefan Nehring,


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