Friday, July 27, 2012

Here a Periwinkle there a Land Snail, but the Snails ain't from here

On July 26, 2012 we had the opportunity to go to Lovell's Island in Boston Harbor during low tide.  It was the first overcast day that we had during the course and it was a bit of a struggle to get out to Lovell's, but the DCR saved the day.  The crew of the Abigale and the DCR were kind enough to send us a boat to take us to Lovell's Island and wait for us while we went exploring.

The beach on Lovell's is a sandy beach.  This was the first sandy beach that we had encountered during our trips.  The sand was washed from the back side of the island to the front side of the island by the power of the sea.  The sand is mostly a dark charcoal gray color and if you look very closely there appeared to be a large amount of broken mussel shells mixed in.  We did note that they mussel shells on this beach had far less fouling organisms on them and a theory was discussed with Professor Burman that the location of this particular part of Lovell's island is located on a channel with a very strong current that may have swept the fouling organisms past this part of the beach therefore leaving these mussels less fouled.  The mussels were of course blue mussels that we have seen at our other locations.

As we moved along the beach it gradually went from a sandy beach to a cobble beach.  There were a number of live slipper shells on the beach and Burman had the privilege of sampling one of these Lovell's Island oysters directly from the shell.  The slipper shells tended to be pale in color almost flesh toned with stripe of lavender here and there.  They would piggy back on rocks as well as each other.  Below is a picture courtesy of Google images. 
As we rounded the bend a great scene of tide pools laid before us.  In the tide pool we experienced much of the same life that we had been seeing at the other locations we had visited.  There was a plethora of hermit crabs scurrying from  here to there and some actually being aggressive towards each other.  They were in various periwinkle shells that ranged from brown or green black to paler shades of peach or white.  In these pools we also came across a colony of tunicates that was much larger than what we had seen at the dock or other beaches.  We also found some sea urchin skeletons, Asian shore crabs and what may possibly be an isopod of some sort. These are shown below.

(Thank you for the images Liza)
After playing in the tide pools for a while and seeing periwinkles that had multicolored shells that ranged from brown, green black, pale yellow and even some light bluish colors.  we went up and took a look at the salt marsh which was more active and green than the one that we saw on Peddock's island because we had just received some rain.  I did notice birds flying in and out of the grass.  On our way to end our journey  we came across some shells of a different color.  How could they get here?
 Once we began walking the path through the woods back to the boat we learned that these shells are from the Grove Snails (found in a previous class blog) and they live in trees.  They are invasive and probably came over with the flora (sumak) that was added to the island by early settlers.
Their shells are lighter in color and much thinner than the marine snails on the beach.  My theory of how they got to the rock is that they are a favorite food of Song Thrushes that can be found in New England during the summer time according to:  The birds of New England and adjacent states by Edward Augustus Samuels.  The birds could take the snails to the rocks to crack the shells and get the flesh easily.

Another great trip in the harbor!  Thank you again DCR and the Abigale!

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