From Sea to Sea: Effects of Invasive Species in Marine Systems

Non-native species have invaded over 80% of marine regions on Earth, including remote Antarctica. Over half of these species are considered harmful in their invaded habitats, causing changes in native marine ecosystems and exacting stiff economic costs from marine industries such as shipping and aquaculture, two of the main pathways for introductions. Control methods are particularly challenging in the fluid ocean and thus marine invasive species management rests heavily on prevention. As countries adopt the international convention for the management of ship ballast water and the aquaculture industry strives to follow international codes for introductions and transfer of marine species, the prevention emphasis has shifted to other important pathways, such as hull fouling and the aquarium trade, and to emerging pathways such as plastic debris. The effects of marine invasive species are myriad: toxic microorganisms such as dinoflagellates and the cholera bacterium can affect human health while other species can change food webs and disrupt ecosystem services provided by marine wetland plants (salt marshes, seagrasses). Public attention has been diverted away from marine invasive species as awareness of ocean climate change grows, despite the facts that marine invaders are spreading twice as fast as marine species are shifting poleward as oceans warm, and that policies and protocols have been established for marine invasive species management, unlike the daunting challenge of mitigating climate change. Ocean warming compounds the problem of marine invasive species by opening new routes for invasions, such as the Northwest Passage which has been ice-free since 2007, and by favoring the colonization, survival, and growth of some invasive species over native species. Marine ecosystems should respond more easily to a rapidly warming ocean if they are protected from invasive species and other disturbances that can be effectively managed.