Assignment 2: Land Snails

07/18/14

Hello Again!

The second part of the assignment consist on identifying the shells we found on the huge rock at the end of our tidal pool observations. We also have to conclude on how these terrestrial snails got to that part of the island. 

Let me first start by identifying the shells we found. There were two types of shells, in which prior to their landing on the rock, belonged to two specific species known as the Brown-Lipped Snails (Cepaea Nemoralis) and White-Lipped Snails (Cepaea Hortensis).

The first shell I saw and observed belonged to a Brown-Lipped Snail. The reason I know this is because the color around the original shell's opening was brown. I mention original because this specific shell had two openings, in which one of them was intentionally done by another animal. The shell's colors were purple and white and it had two think brown spiral lines along the body of the shell. This specific shell was about 2.5 cm long. After doing some research, I found that the shell of this snails vary in color and are larger than the White-Lipped Snail's shell. Also, this specie can be found all around the Boston Harbor Islands, specially around vegetation. 

The second shell I saw belonged to a White-Lipped Snail. There are just a few differences between this shell and the one mentioned above. This shell had a white color around the original shell's opening, which is the reason of their name. Also, the shell was a bit smaller than the first shell I described, about 2.0 cm long, and its colors were white and light brown with about three spiral lines along the body of the shell. (This shell also had an intentionally done opening on the shell)

Interesting facts are that both of these terrestrial species have both female and male reproductive parts, they can live up to nine years, and they bury themselves into the soil during the winter time. 

When it comes to analyzing how these shells/snails go to that part of the island, where no vegetation (their habitat) is found, there is only one conclusion to make; they were brought there by an animal. This animal could be any bird that feeds from snails. As I mentioned prior, the two shells I observed had one intentional opening at the opposite side of their original openings. With this being said, what makes sense to me, is that the bird was trying to eat the inside and brought the snail to the rock were we found them. By doing this, the bird had a solid location in which he/she was able to use its peak to make this openings in order to eat the snail. As you all can recall, there were many shells at the Fan Pier Cove and was determined that birds had brought them there to feed themselves. On this occasion, the same is happening. The bird went to a "familiar" place where he/she knows that no other animal will interrupt its feeding process. Also, it is important to note that birds are one of the most important predators of territorial snails. Even though there are other "enemies" for these species, no other animal is able to fly or capable of bringing such shell to such a remote location.

So many species and so much to learn =)

Sources:

http://insects.oeb.harvard.edu/boston_islands/mantisweb/botm/0903_brnlppd_snail.php

http://www.arkive.org/white-lipped-banded-snail/cepaea-hortensis/
http://www.snail-world.com/snail-predators/

Daniela Baeza-Prepetit