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Invasive Species: What We Do

Marine Invaders

Most of the invasive species that have taken hold around the world are difficult to remove.


See Marine Invaders

See striking images of marine invasive species found around the world.


A population of unassuming comb jellyfish was sucked into the ballast of a U.S. tanker and shipped halfway around the world in 1993, where it was unceremoniously dumped into the Black Sea when the tanker discharged its ballast water.

This seemingly innocuous event caused one of the most alarming species invasions in European history. At their peak in the mid-1990s, the comb jelly invaders made up 90 percent of living organisms in the Black Sea — the sheer weight of the invasive population exceeded the weight of the world’s entire fish catch. The jellyfish destroyed the Black Sea’s commercial fishing industry and cost thousands of jobs. 

Marine Invaders: A Worldwide Threat, Says New Conservancy Study

A new study from The Nature Conservancy says this alarming occurrence was not an isolated incident. In fact, 84 percent of the world’s marine ecosystems have been infected by invasive species — and this number could be even higher due to under-reporting.

The study also found that most of the invasive species that have taken hold around the world — from San Francisco Bay to the eastern Mediterranean Sea — are difficult if not impossible to remove. Other major findings of the study include:

  • Many marine invasives harm other species and disrupt entire natural systems.
  • 57 percent of marine invasive species in our study can be classified as harmful to the native ecosystems.
  • Most invasive species are unintentionally transported to new habitats through shipping.
  • Many species are introduced through the farming of non-native fish and shellfish. 

Although only a small fraction of the many marine species introduced outside of their native area are able to thrive and invade new habitats, their impact can be dramatic and have transformed marine habitats around the world. The most harmful of these invaders displace native species, and change natural structures and food webs.

Alien invasive species can also significantly alter human lives, and have damaged economies by diminishing fisheries, fouling ships’ hulls, and clogging intake pipes. Some can even directly impact human health by causing disease.

Invasives: Deal With Them Before They Invade

Stopping invasions before they happen makes economic as well as environmental sense, as the catastrophe in the Black Sea demonstrates.

But dealing with invasions when they occur is very expensive and rarely effective. For example, the United States spends $120 billion annually on the control and mitigation of impacts of more than 800 invasive species infestations across our lands and waters.

Invasives typically hitch rides to new habitats either through the discharge of ballast water which ships carry for stability or through the "bio-fouling" of ships hulls, when aquatic species hitchhike to new places on the bottom of ships. Coordinated action from governments is needed to prevent further introductions through these pathways.

The new report provides evidence to support ongoing efforts to improve ballast water management practices and to tackle the problem of the fouling of ships' hulls and lines. However, the major impacts of ship-fouling species suggest that ballast water agreements alone may be insufficient.

The study also confirms the role of aquaculture operations such as non-native fish and shellfish farming in marine invasions. Stricter, industry-wide control measures should be developed and enforcement strengthened to restrict intentional and accidental introductions of harmful invasive species.

The study could also inform biosecurity decisions by helping identify species that have not yet invaded an ecoregion but have had considerable impacts on similar habitats elsewhere. 

Government Action Needed

It is vital that governments begin working now to make  strong decisions on invasive species that will halt new introductions around the world before this hidden threat becomes more costly to people and nature.

To counter the devastating effects of invasive species around the world, the Conservancy is encouraging governments to make a strong decision on invasive species that will

  • Halt new introductions through priority pathways;
  • Support screening of new species before they are introduced; and
  • Ensure countries have the technical and financial resources required to combat invasions.

And governments this year have an unprecedented opportunity to address these issues: Marine invasives will be a top agenda item at a meeting in May of the UN-sponsored Convention on Biological Diversity in Bonn, Germany. 

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