Monday, August 3, 2009

Lovells Island

Yesterday, August 2, 2009, consistently about 75 degrees and slightly gloomy, we spend the late morning and afternoon on Lovells Island. Beginning by examining some shells on this cobble beach, we learned that most things living on the island live below the high tide line and the tide goes out about 1 foot every half an hour. We learned that the top of the tide line is called the “wrack line” which is where much of the seaweed is left. The things that effects what we see on the beach include the currents which move the sand, human activity (for example, building sea walls), and tides and storms. Walking along the beach we collected blue mussels which differed in color depending on how long they had been at the beach. We then identified and collected periwinkle shells based on their stripes, color variation, and shape. We learned that small snails, like these periwinkles, may have originated in Europe and are possible the most destructive, invasive species, according to some scientists. After observing the small drilled holes in the snail shells we discussed where the snails might live and establish that some snails have lungs, some have gills, and some have both.
Later in the afternoon, we came upon a dry, grassy patch of land which had been a salt marsh but dried up because of a lack of water. Out of two invasive species we thought existed there we examined one which was Pepperweed. We then went to a tidal pool where we say a lots of bird life, mussel shells, many crabs, and clusters and clusters of snails in the shallow water and rocks. The tidal pools also had the blackish yellow Rockweed growing on rocks on the sand and scattered around the land, probably from the wind. The Rockweed on the rocks was wet and we could conclude that at high tide it was underwater. After the tidal pool we walked through a dryer part of the island with more plants and trees. We came upon some live snails on the trees but mostly snail shells on the ground that resembled the ones Bruce “found” on the beach while we were eating lunch. These shells differed from those of the periwinkles because they were flatter, not as long, much lighter, were different colors, and had different colors bands going around them of various widths. For the last part of class we returned to the tidal pool and some of the classmates examined the contents of what was in the water.

Questions of the day:
Trying to identify what drilled the holes in the periwinkle shells, I found that predators of periwinkles include the Sea Star which is the most dangerous, crabs, and shore birds. I was not able to track down any definitive information on what caused these holes but it could be the work of crabs because we definitely saw plenty of crabs on the island. I looked at some pictures of Shorebirds on the internet and although I could not find much information about their diet, they looked like they had very sharp pointy beaks, so perhaps these beaks pierced the holes in the periwinkle shells.

The other tiny snail we spotted on the cobble beach was shaped differently then the periwinkles, almost like a corkscrew or spiral. Looking through the guide, I am guessing it may have been a Greenland Top Snail because of its size region, and habitat. Also, the description mentioned that this snail has two color phases, one of which was a creamy-tan, which if I remember correctly, was the color of this snail.

My best guess is that the snails that we saw today on the path, and whose shells were on the beach, are Grove snails. After do an image search on Google for snails and snails with stripes I found several kinds that looked like the ones we saw. One kind was the Hedge Snail which included in its family black-lipped and white-lipped snails. Although they looked like the ones we saw, I read that they were found mostly in the British Isles and other parts of the Europe. The Grove snails, although also European, has recently come to North America, so these might be the snails we saw.
Throughout my research I have read that certain birds eat certain snails. Although I am not positive that we saw Grove Snails, and furthermore do not know the specifics of which birds eat which snails, one theory of how the shells got to the beach where we first spotted them is that birds caught them, ate their dinner somewhere, and then dropped the shells of on their way somewhere else, and they happened to land on this beach. Of course when I say birds put them there I actually mean Bruce put them there, but perhaps birds could theoretically have left these snail shells there for this reason.

The crabs we saw in the tidepool may have been Green Crabs. Looking through our guidebooks the fan shape of the Green Crab and its description seemed to resemble what I saw yesterday, although I am sure there were at least several types of crabs where we were. Also, the habitat of the Green Crab which includes rocks and tidepools, the range of where they exist, and their size, all seem to fit appropriately with what I saw.

The differences in the color and pattern distribution between the live and dead snails, according to the photos, seems to be that there was more variation in the dead snails. The live ones were basically the yellows and browns, and there were not really any light pinks among them. So perhaps these snails with yellow and brown patterns can survive better in this habitat, and maybe this is because their colors more closely resemble other parts of the surrounding habitat, and therefore predators cannot spot them as easily. However, we did see more of these brown and yellow dead snails, in comparison with the light and pink ones, so this can mean that there are simple more of these snails on the island, and even on the earth.

As for the blog from the Barking Crab, I realize that one of things I saw yesterday and I identified as a Wine-Glass Hydroid was probably not, because looking back I discovered that they are not found in this region. Something else that I probably wrongfully identified from the Barking Crab was what I deemed to be a Eunicea Sea Rod. Again, they are not found in this region, and whatever I saw was only a few inches, while the Eunicea Sea Rod, the Guide tells me, is several feet long. My bad. However, what I identified as the Golden Star Tunicate on the piece that Bruce held for everyone, I believe is in fact that because the region, size, and description all match, and the picture of it looks exactly like what I saw.

See you all in the class soon.

Leana Ovadia

No comments: