Invasive SpeciesGreen crab

Carcinus maenas
FOUND by christinev
2013-05-10
Portland
ID Confirmed
Quality checked by manyeyes
Peer reviewed by
Field Notes
Students from Dover, NH's Cocheco Arts and Technical School and Falmouth High School competed in the Nor'Easter Bowl and earned a chance to join us for a day in the lab at GMRI. It was great to have them here, and they collected some great data to help us continue to track the crabs living off the end of the dock here at GMRI. The weather cleared up just in time for us to head outside. It was warm and sunny, definitely in the 60s. Adam dropped a trap down yesterday. After approximately 24 hours the trap came up with 18 crabs. All the crabs appeared to be green crabs. We learned that the triangle on the underside of the carapace is wider for females, and they all appeared to be female.
A sketch of our study site.
Supporting Evidence
Photo of my evidence.
One great way to ID green crabs is by counting the spines on the carapace. Green crabs have 5 spines outside each eye. Native species have 8-10 spines and other invasives have fewer than 5 spines. In all 18 crabs we counted 5 spines like you see in the one shown here.
Photo of my evidence.
Green crabs have thin claws with sharp tips like you see here. One crab had disproportionately small claws, but they still fit the thin and sharp description. They are also aggressive. One even bit smo!
Photo of my evidence.
Green crabs have a pentagon shaped shell. You can see that this shell is very pentagon-ish. Native crabs have more oval-ish shells, and other invasives are more round to square-ish. We all feel pretty confident that we had 18 green crabs.
Species Observation: Species Looked For
Did you find it?: 
I think I found it
Scientific name:
Carcinus maenas
Common name:
Green crab
Sampling method: 
Trap
Photo of our sampling method.
Place Studied
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Map this species
Latitude: 
N 43.650123 °
Longitude: 
W -70.253617 °
Observation Site Information
A photo of our study site.
Habitat: 
Coastal - Dock
Trip Information
Name:
End of GMRI/Coast Guard dock
Trip date: 
Fri, 2013-05-10 11:00
Town or city: 
Portland
Type of investigation: 
Species Survey
Ecosystem: 
Coastal
Watershed: 
Presumpscot
Time of low tide: 

Comments

Submitted by fblock2 on Thu, 2013-05-16 12:32.

nicely done

You're field notes are really great and specific. I really liked how much detail you put into them. The close up of the green crab was nicely taken and it was interesting to see the barnacles on the crabs shell

Submitted by christinev on Thu, 2013-05-16 13:08.

Thanks! It was really a team

Thanks!

It was really a team effort as you can see from the photo in the field notes. :)

I thought that crab shell with the barnacle was particularly cool myself.

Thanks again for checking out our data.

Christine

Submitted by Crab Lady on Sun, 2013-05-12 15:00.

Thanks for the great notes

Thanks for the great notes and photos!