Mean Green Crab Machine – An Alien Invader

The European Green Crab (Carcinus maenas) didn’t arrive in a UFO, it hitched a ride on ships and made its way to the Atlantic and Pacific coasts of North America all the way from Europe and Northern Africa. The adult green crab is about 6 cm long and 9 cm wide. In 1989 green crabs were spotted on the Pacific coast of the US (FOC, 2009). By 1999 they had reached British Colombia and recently appeared in Newfoundland waters (FOC, 2009).

Retrieved from “Small Lagoon Fights Off Occupation”

Virtually Indestructible

The green crab, unlike other crab species, can rotate its claws over its back in order to defend from any predators attacking from behind (FOC, 2009). Its legs are flattened to help them swim at quick speeds. The green crab can survive out of water for an entire week and even in full sun! (FOC, 2009) Think that’s not good enough? Green crabs can survive for short periods of time in fresh water as well. Maybe the Philosopher’s Stone wasn’t destroyed by Dumbledore after all?

They have huge appetites and eat pretty much everything in their path including, mussels, scallops, oysters, and small lobsters.  Green crabs can survive in a wide range of temperatures, from below zero to more than 30 °C (FOC, 2009). Females can spawn up to 185 000 eggs a year (FOC, 2009). The hatched eggs drift in the water column for approximately 90 days then hatch. Green crabs live for 4-7 years and reach sexual maturity at age 2 or 3 (FOC, 2009).

What is Molting?

Retrieved from “Molting: How Crabs Grow”

Molting is how crabs and other crustaceans grow. Their hard outer shell (exoskeleton) does not grow and therefore needs to be shed. Before the crab molts, it absorbs seawater in order to expand which helps it detach from the old shell. Molting also has other benefits including getting rid of parasites, and other animals on the shell, but also leaves the crab vulnerable during this time.

Taking over

The green crab is threatening habitats for native organisms and impacting biodiversity (FOA, 2010). They steal almost all of the available the food, but also burrow and damage roots of plants. Early research shows that the green crab is replacing the native rock crab. The green crab has no natural enemies. A study written by Erin Breen shows the effects of the green crab on 2 native crabs in Nova Scotia. To read her journal article click here

Retrieved from “Project UFO: The search for the unidentified Foreign Organisms”

Sounds like green crabs aren’t much good for anything. Maybe not? Researchers are currently studying the use of green crabs in fish feed because they are high in protein and carotenoids. Read more information at The Fish Site blog, click here (

Questions to Ponder

Are humans the green crab’s only enemy?…are we going to have to control these organisms so they don’t take over completely? One blogger explains how volunteers are controlling green crab populations by physically removing the crabs. Since 2009 57 600 crabs have been collected (Noble, 2011). Read more here

Drawn by Justine Doherty

Here is a fun video showing how crabs walk

Me with a green crab from the Aqualab!


Breen, E. A. (2009). Effects of the non-indigenous european green crab, carcinus maenas, on two native decapods in the bras d’or lakes, nova scotia. Dalhousie University (Canada). ProQuest Dissertations and Theses,173.

Fisheries and Oceans Canada (2010). Aquatic Invasive Species: European Green Crab In Newfoundland Waters. Retrieved on September 30, 2012 from

Fisheries and Oceans Canada. (2009). Green Crab. Retrieved on September 30, 2012 from

Noble, M.  (2011, December 6). Small Lagoon Fights Off Occupation. Retrieved from

Project UFO- The search for the unidentified Foreign Organisms. Retrieved on September 30, 2012 from

Stevens, B.G. Molting: How Crabs Grow. Retrieved on September 30, 2012 from

TheFishSite News Desk. Researchers Study Use of Green Crab in Fish Feed. Retrieved September 30, 2012, from

Leave a Reply

Please log in using one of these methods to post your comment: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s