Invasive species: Can they help restore degrading habitats?

By May 21, 2013 Ocean News

One of the most destructive invasive species in Europe is the American crayfish (Procambarus clarkii), and in America the most destructive invasive species is the European green crab (Carcinus maenas). You can find this crab in almost every coastline in the world. They are very aggressive in that they can eat every kind of food and they chase and kill native species, which sounds terrible. But…

Can they do any good to an habitat? The answer is YES, they can.


Researchers from Brown University noticed something interesting in Cape Cod, Massachusetts. A salt marsh had been degraded due to overfishing, where salt marsh predators were removed allowing the population of purple marsh crab (Sesarma reticulatum) to feed on cordgrass (Spartina alterniflora). The purple marsh crab population was responsible for eating hundreds of hectares of marsh lands. This is considered a huge problem as salt marshes are known high biodiversity of species hiding within the cordgrass.

The saving grace was due to the invasive European green crab, which out competed the purple marsh crab for the burrows they built driving the purple crabs out of the area and allowing the cordgrass population to grow back to a healthy size and restoring the salt marsh.

Mark Bertness designed an experiment to understand the interaction between both crabs. They surveyed 10 salt marshes last year, and they proved that the recovering ones had a higher density of green crabs. Also, they placed the two species together in cages. About 85% of the purple marsh crabs died in the cages proving the green crabs out competed the purple marsh crabs. But there’s more, because most of the purple marsh crabs were afraid of the green crabs, and they didn’t even go out of their burrows in the entire month of the experiment. It didn’t matter if the green crab was next to the burrow, but caged. Thanks to this, the cordgrass had a break to regrow.

This story is a great example where an invasive species, often seen as destructive, served to restore an ecosystem. This obviously does not happen all the time, but maybe this situation is not unique! More research is needed to study the impacts of invasive species on recovering habitats.

Do you think invasive species should be used to help restore degrading habitats? Let us know in the comments below!

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Join the discussion 4 Comments

  • But what happen after restoration there any way to control those invasive species crab or they will simply eat all native species?

  • Andrew Lewin says:

    The green crabs are an invasive species so they are not used to stop the purple crabs from eating the cordgrass. This situation seems to be one where the green crabs were present already and the researchers made some scientific observations through some experiments. There have been situations where people have introduced species to help them get rid of another species or eat algae (an example of this is the introduction of asian carp to the Mississippi River to eat algae off of the aquaculture nets; however, the asian carp population boomed; destroyed the environment; and, is now threatening to invade the Great Lakes!).

  • Paulo OConnor says:

    Yeah…I find non-peer reviewed articles describing one-off results from weakly designed small sample size experiments that claim to “prove” anything, to be as destructive as invasive species themselves.

    I too in my own research found an assumedly destructive invasive species did have some unexpected possibly temporally positive influences on some aquatic native species present, but this did not mean the long term destructive effects of the invasive were lessened in any way. Nor would I have represented my results as ‘proof’. As far I remember as scientists we never ‘prove’ anything.

    My recommendation is to remove this unprofessional article that carelessly states arguable facts, from what really should be a more serious discussion group.

  • Andrew Lewin says:

    Thanks for your comments Paulo. The article we wrote is based on research others did. This article is not a product of research done by We are merely communicating the type of interesting research that is happening in Ocean Conservation that we find important.

    We always encourage our readers to state their opinion on the articles we right to start a discussion. We do not submit any research to peer-reviewed articles.

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