Trouble in the Tides.

For being such a bold intruder the green crab shows little courage when confronted by my harmless hand. Upon trying to inspect this troublesome crustacean in the Aqualab, it retreats to the safety of an underwater shelter. After avoiding its pinching claws and thrashing legs I can finally hold it and see what many people are trying to eradicate. This unimpressive sea creature has obtained an awful reputation by being one of the worst invasive species on the planet. In Canada it is threatening marine ecosystems by devouring nearly anything and everything it can get its claws on. Below is a video that can familiarize you to this alien species:

How does it establish itself in new locations?

The green crab (Carcinus maenas) is a native species of Western and Central Europe that has tagged along on ships and cargo to disperse across Australia, North America, Africa, and South America. Growing up to three and a half inches, it feeds on a wide variety of prey from bivalves to juvenile fish to other crustaceans. By being an extremely efficient environmental conformer and each female laying roughly 180000 eggs, it can survive and proliferate in a huge array of environments.

Figure 1. A juvenile green crab.

Why are they such a threat?

Given their size, one might assume that native species of crab that are larger or of equal bulk would out-compete or dampen the negative effect the green crabs are having on marine ecosystems. What was found in a study by Miron et al. (2005) was that green crabs are more voracious predators, eating a wider variety of organisms, and frankly more of them. To see the full paper and statistics of the research, here is a link to the complete article: Miron et al. (2005). Ecosystems are not adapted to this ravenous species and cannot support their large appetites for almost everything that moves.

So what’s the plan?

What I would like to know if what is being done to buffer the expansion and destruction of the green crab throughout coastal Canada and other parts of the world. Is there a native species that can be harvested to out-compete or prey heavily upon them? Is there a lethal parasite that can be isolated to only infect green crabs? For now anyways, governments, industries, and communities are teaming up to impede their dispersal and completely remove them from local ecosystems. An example of these efforts can be seen in this blog by the Smithsonian Environmental Research Centre. Whether these attempts are in vain or if will actually help to control the green crab population is yet to be seen in future studies.

Figure 2. A sketch of an adult green crab by Sam Rawluk.

Samuel Rawluk – 0716042


Miron, G; Audet, D; Landry, T; Moriyasu, Mikio. (2005). Predation potential of the invasive green crab (Carcinus maenas) and other common predators on commercial bivalve species found on Prince Edward Island. Journal of Shellfish Research, 24, 579-586.

Noble, M. Small Lagoon Fights Off Occupation. Shorelines.                                  Retrieved September 28th 2012 from:


Green Crab discovery with Tidepool Tim, Gulf of Maine, Inc. Retrieved on October 1st, 2012 from:

Photo credit:

Figure 1. Retrieved September 28th 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