Friday, August 10, 2012

An Inconvenient Species

Everyone has been enjoying the numerous sea animals that can be found at Black's Creek, especially the kids, but there's always one reoccurring species that is both a fascinating sight, as well as a true pest. That would be the infamous European green crab (Carcinus maenas).

Nothing but green crabs at Black's Creek, day after day!
A detailed close-up of the green crab's carapace.
Native to European and North African coasts, the green crab was first sighted in North America in 1817. The first sighting happened to be in Massachusetts. They are now considered the world's most successful aquatic invaders.

Blue marks the native range, red marks where they have been introduced, black dots mark where there was a single sighting but did not lead to an invasion, and green areas mark the potential range of the green crab.
So what exactly is an invasive species and why is it so bad that green crabs are here? First off, an invasive species is "an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health."

Green crabs are #18 in the list of the world's worst 100 invaders, but how do they harm the ecosystem they invade?

Green crabs are known as a voracious predator, which means they are extremely aggressive and consume large quantities of food. They are known to threaten mussel farms, pose significant impacts on native species such as mollusks and other crustaceans by predation, competition and habitat modification, and they were one of the causes of the collapse of soft-shell clam industries. In just the US alone, green crabs cause about $22 million dollars worth of damage... each year!

They are also known to decrease the biodiversities and biomass in each community they invade, and they certainly have been doing just that at Black's Creek.
"Aaarrgh!! This is my territory now!!" 
The kids love racing the green crabs.
Many techniques have been used to try and reduce the green crab's population, but its safe to say they will be with us for a very long time!

- Carly

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