Tuesday, August 3, 2010

Lovell's Island

Hello All,

We were lucky to reach Lovell’s Island at low tide, which allowed us to explore a large portion of the inter-tidal zone. Several tide pools had been formed, including two large ones. The main difference between the Lovell’s location and the Barking Crab location is that the underside of the docks remain consistently underwater, and are therefore sub-tidal, however many of the areas we explored in and around the tide pools are often exposed for part of the day, thus making them inter-tidal. The water temperature varied greatly depending on the depth, and tide. The small pools which were close to shore and had been sitting in the sun were noticeably warmer than the large pools further out. The depths of pools varied from as little as 3-4 inches up to 3 feet. The water was quite clear compared to other areas we had visited. The shoreline was partly cobbled beach and partly sandy beach.

As for biodiversity: I saw evidence of a number of species, by collecting live samples, and also by finding shells of other species. The living species clearly inhabit the tidal zone, whereas the shells could have washed ashore from species that live in deeper waters.

I found some Blue Mussels, like at the Barking Crab, except these were scattered individually along the floor of the tide pool, whereas the mussels from Saturday were often in bunches and attached to the dock.

We all observed copious amounts of Periwinkles, an invasive species. It was difficult to coax them out of their shells, but after a little humming, I was able to observe two antennae on the head of the snail.

We found stacks of Common Slipper Shells, measuring between less than 1/3 of an inch to 1 ½ inches.

I found one other species of live mollusk, which I lost when my partner overturned my specimen container! It was small, less than a centimeter across, but I believe it may have been a Tortoiseshell Limpet, since it had a very distinctively colored shell. According to Peterson’s guide, this limpet can inhabit inter-tidal waters.

As for other species, I found several Asian Shore Crabs, which I described in my previous post. These ones were significantly larger, measuring about 2 inches across. It is interesting to note that they were all found very close to the shore, well within the inter-tidal zone, whereas the small one we caught near the Barking Crab was living under the dock in a sub-tidal zone. We found both males and females, differentiating between the “rocketships” and wide triangles.

We found two types of plant like animals distributed throughout the tide pools. One was an oblong sea squirt like creature, which was attached to a rock by a long stalk. I think this may have been some variety of a Stalked Sea Squirt. There was also an orange sponge like tunicate, which I was unable to identify to my satisfaction using Peterson’s guide. I then turned to hitchhiker’s guide, thinking it must have been an invasive species. My suspicions were confirmed when I found the Orange Sheathe Tunicate, which fit the description of what I saw, and is common to the shallow inter-tidal and sub-tidal zones.

As for the perfectly round holes we found in the shells of periwinkles and other mollusks. I suspect that these holes were caused by either a predator, or a parasite. According to Peterson’s guide, the Channeled Whelk, which is the largest sea snail in the area, feeds on other mollusks by “using their shells as hammers to chip away an opening.”(133).

As for our Grove Snails, which (thanks to Pearl) I learned are divided into two groups, the brown lipped and the white lipped. I am not entirely sure how these reached the edge of the beach and congregated on that one rock. One theory, that predatory birds dropped them there in order to crack them open and eat them, is very plausible. However, I didn’t notice that the shells were significantly damaged, which leads me to believe that they weren’t dropped there to break them open. Perhaps the snails traveled to the edge of the wrack line in order to obtain minerals and salt that a particularly high tide had left behind? As for differences between the land and sea snails, the most obvious to me was the thickness of the shells. The periwinkles, which are tossed by the tide and living in a somewhat harsher environment, would need a thicker shell than the grove snails.

Due to technical difficulties, I wont be able to upload my pictures until later in the week. More to follow!

Amir Farhadi

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