Monday, October 15, 2007

Critters! Some large, many small.

Pictures from the field:

Date: October 6, 2007

Specimen ID:
2 specimens of Large Hermit Crab,
Pagurus pullicaris

Front specimen hermitting a medium to large Moon Snail shell (Lunatia heras)

Rear specimen hermitting a medium to small Channeled Whelk shell (Busycon canaliculatum)

Collection Location:
Specimens were collected in the shallow subtidal zone during low tide from southeast side of Assateague Channel at Assateague Point. Specimens were taken back to the laboratory where they were observed and studied in aquaria.

The large hermits are usually identified on the basis of their larger size, the dominance of the right claw (also used as the door when it retreats into the shell) and by the presence of tubercles.

Many hermits- including the one in the Channeled Whelk Shell are often encrusted by a number of different epibionts (organisms that live on top of other organisms) ranging from algae, to bryozoans, cnidarians, bivalves, barnacles, etc.

During the night after collection, the large hermit crab underwent ecdysis and shed its exoskeleton in the aquarium. The following morning the crab was pale white and by late afternoon the greenish brown color had returned to its carapace indicating that the exoskeleton had become harder. Moreover the crab was noticeably larger in size.

Specimen ID:
medium sized male Blue Crab, Callinectes sapidus

Collection Location:
This specimen was collected in the lower intertidal zone in a small pond isolated from the main channel. Locality info as above.

Along with several larger live specimens, students collected a number of dead and molted specimens ranging in size from juvenile to large adults. Most crabs were evidently males although one dead female crab was discovered.

Several specimens were collected and returned to the lab for observation. During this time, the larger crabs were isolated from other species and smaller individuals. Nonetheless, one small blue crab was put in an aquarium with several other species of aquatic crabs including a Green Crab (Carcinus maenas) and several Rock Crabs (Cancer irroratus). Even though they were about the same overall size ~ 2 inches in carapace width, after the first night, two of the Rock Crabs were found to be missing from the aquarium. Later that day a third rock crab as well as a Green Crab were found to be clutched in the claws of the Blue Crab. Although it was not expected it was evident that the crab had successfully preyed upon the other crabs. Remarkable predator indeed.

Specimen ID:
Young Diamondback Terrapin, Malaclemys terrapin

Collection Location:
This specimen was rescued by students during the cleanup of Tom's Cove Marsh. This turtle had become entangled in the commercial predator netting that had been washed into Tom's Cove.

This specimen is perhaps two years old based on its smallish size and the appearance of the growth rings on its back. It would not have lived to see another year. The turtle was already emaciated and somewhat dehydrated by being caught in the netting material obviously for some time. This specimen could have been a female as its head was fairly blunt, although as it was a younger turtle it is still not conclusive until it is of reproductive age when the body shape becomes much more pronounced between males and females.

This turtle species is making a recovery after having been significantly depleted as a food resource. Although it is still consumed in some restaurants as a delicacy, the biggest threat to terrapins is coastal development in hatching grounds, and automobile related deaths as they are run over during the migration to breeding grounds and hatching areas.

Specimen ID:
Eastern Mud Whelk aka Eastern Mud Nasa
(Ilynassa obsoleta)

Collection Location:
Tidal flat northeastern side of Assateague Point, Assateague Island.

This photograph shows large numbers of the small gastropods and their trailways as they move around on the exposed tidal flat during low tide. Classified mostly as herbivores, these snails are grazing on bacterial and algal mats which are growing on the silty sediment grains. It was also found scavenging on small pieces of organic detritus and in one case small pieces of crab.

Specimen ID:
Bald Eagle (Haliaeetus leucocephalus) sitting in the crook of a maritime pine tree Pinus serotina

Photograph Location:
North fringe of the maritime forest at Assateague Point facing Assateague Channel.

Students discovered this eagle sitting in the crook of this tree. Close inspection showed a few small bits of fish were still hanging on the branch of the tree where it was sitting. Undisturbed by the students, this Eagle was not feeding when it was first observed and it appeared to have been resting. Upon later communication with an ornithologist on the island, it appears that this bird was not one of the three pairs of eagles nesting on Assateague as they have already left for their migration. It was his speculation that mature adult bird was also in migration and stopped for a brief rest in the refuge.


Susan said...

Thank you for this wonderful blog. Thanks for saving the turtle and sharing the story of the eagle. Your work is appreciated. Bravo.

Emma said...

I find it humorous that your crab species dined on one another. The blue crab obviously cannot be underestimated. Also, I had the oppurtunity to see a bald eagle in the wild and they are quite the site. It's nice to see them making their come-back. I hear in Alaska, they are as abundant as crows.