Green crab
Carcinus maenas
NOT FOUND by Steph2012-08-14
Portland
ID Confirmed
Quality checked by team 2
Peer reviewed by
Field Notes
It was nearly high tide on a sunny, hot, hazy summer morning. What a treat to be out on the water with the Lucky Catch. We saw a harbor seal on the way out of Portland and plenty of gulls. The harbor was fairly busy with recreational and commercial boats. Both power, sail, and self-propelled boats passed by our vessel. The water was quite calm. The trap was set on a sandy bottom at a depth of 33 feet right off of Portland Head Light. The trap was made of yellow wire. It was just about high tide at the time of our sampling. Today, we were investigating whether the native species would out-number the invasive species. We predicted that we would find a greater number of native species than invasive species in the traps. Our data, as well as the data from three other groups, supports our prediction. Our trap contained seven native species and two invasive species. In each trap the number of native species was higher, ranging from 6-11 native species, versus 0-2 invasive species.
Supporting Evidence
This is not a green crab. All of the crabs that we saw had more than five spines on the outside of each eye, while green crabs have five spines beyond each eye. A greater number of spines points to a native crab species, which typically have 8-10 spines. These spines look like tiny protrusions or bumps,at the front of the carapace, or shell, of the crab. Examine the lower right part of the photo to see the spines.
This crab had a carapace whose width was 10 centimeters and whose length was 6.5 cm. Native crabs have widths that are much greater than their lengths, while green crabs have widths and lengths that are similar in size. The carapace is the exoskeleton of a crab. It encases the body and must be shed for growth. These crabs had spotted carapaces. Our crab was not green, although color is not necessarily a reliable means of identification.
Green crabs are aggressive, fast, and they brandish their front claws when threatened. Our crabs were sedate and easy to handle. They did not attempt to get away, fight our handling, or make any effort to pinch our hands. In this photo, the crab is in our hand, not moving, with legs curled inward. Based on our observations the crabs we examined seem to be Rock crabs, not green crabs.
Species Observation: Species Looked For
Did you find it?:
I think I did not find it
Scientific name:
Carcinus maenasCommon name:
Green crab
Sampling method:
Trap
Place Studied
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Latitude:
N 43.624690 °
Longitude:
W -70.207290 °
Observation Site Information
Habitat:
Coastal - Dock
Trip Information
Name:
Portland Harbor
Trip date:
Tue, 2012-08-14 10:59
Town or city:
Portland
Type of investigation:
Species Survey
Ecosystem:
Coastal
Watershed:
Presumpscot
Time of low tide:
Tue, 2012-08-14 03:22
Comments
Well done! I really enjoyed
Well done! I really enjoyed your detailed description of these crabs. Also I was interested to hear about the number of natives vs. invasives in the traps!