Friday, July 27, 2012
Lovell Island observations
Lovell Island is similar to Peddocks Island in terms of living organisms and also habitat. But this time, the beach was less rocky and somewhat sandy. Also the boundary of terrestrial region and water was not accurate in Lovell Island beach unlike the Peddocks Island. The reason why there are less cobble in Lovell Island can be the conversion is still in progress there. I guess as time goes by, the Lovell Island will become a cobbled beach. Even similar organisms exist in this Island such as periwinkles, crabs, rockweeds, snails, barnacles, tunicates and sea lettuce, this time, the amount of those organisms was surprisingly enormous compared to other habitats. However, although there are huge amount of periwinkles, comparatively there were not different kinds of it. Almost all of them were gray-brown periwinkles, but there were rarely yellow and white periwinkles. I guess they were all the members of the same species.
On the other hand, we saw some snail shells that have different colors on the rocks away from the sea. When we walked into the woods, we saw same kind of snail on the trees. Since we didn’t see those shells in the low tide region but many of them in the terrestrial region, they should be a different kind of snails. I guess it was “Grove snail (Cepaea nemoralis)”. Most prominent predators of these snails were birds and mice according to the study of Rosin, Olborska and Surmacki in 2011. They explained the preferences of birds and mice and the results showed that mice choose small individuals because they use their teeth to break and large shells require more time and energy in order to extract the soft tissues. However, birds break Grove Snails open by repeatedly knocking them on large stones, so small snails are not profitable for birds and they tend to choose large species because of their higher food value (Rosin, Olborska and Surmacki, 2011). This explains how they came to the beach from the top of trees.
Rosin, Olborska and Surmacki. (2011). Differences in predatory pressure on terrestrial snails by birds and mammals. Journal of Biosciences. September 2011, 691–699.