Today was a busy day! We took a ferry to George’s Island, and from there we took a small boat to Lovell’s Island. The island had lot of vegetation on it inland from the beach, including blackberry bushes (much to the group’s delight). The beach that we were on was sandy and then rocky closer to the water. It was also very low tide (that came up rapidly while we were there). Once we were on the beach, we waded through a few different tidepools of varying size, looking for life. The habitat was different from the one by the Barking Crab in a few ways. We were farther out to sea, and the life in the tidepools lives on the bottom of the ocean, as opposed to the creatures at the Barking Crab, which lived attached to various structures. Some things we saw were similar to the Barking Crab. We found mussels and crabs like we did at the Barking Crab, but we also saw some new things, such as lobster and periwinkles. The main difference between the two sites was, I believe, that these creatures live on the ocean floor, while creatures at the Barking Crab can live by hanging off the docks. Of course, some can do both, and that was why they existed in both habitats. The creatures we found include:
A periwinkle that I believe was the Common periwinkle (Littorina littorea), It is by far the most abundant snail in New England has is found on rocky shores between high and low tide lines. Periwinkles are an invasive species introduced from Europe 400 years ago, and they are changing the composition of the shoreline from sandy to rocky.
My partner and I also found some orange sheathe tunicate (Botrylloides spp.) This differs from the golden star tunicate we found at the barking crab because it looks more like one uniform structure in texture and color, rather than the separate shapes that form the golden star tunicate. The orange sheathe tunicate has rubbery crust and is found near the low tide line and below I shallow water, and it is found on the atlantic coast, among other places.
We also found many hermit crabs, which I believe were Long-clawed hermit crabs (Pagurus longicarpus), the most common hermit crab in Atlantic waters. It usually uses periwinkle shells as its home.
We found two asian shore crabs (Hemigrapsus sanguineus), which we identified as males because they had “rockets” on their undersides. I described these in my previous post, because we also found one at the Barking Crab. The two we found today were much larger than the one we found on Saturday. They were about 2.5 inches across. The most distinctive feature of this crab is that it only has three “teeth.” Asian shore crabs, like the common periwinkle, are invasive species.
We also found the common Atlantic slipper shell (Crepidula fornicata). The shell is humped with a shelf on the
inside. They are fixed to rocks. They are usually 1. 5 inches long and yellowish in color. (Source: http://www.britannica.com/EBchecked/topic/548836/slipper-shell.)
One other interesting thing that we noticed was that there were many shells with what looked like drill holes in them. I believe that this could have been caused by a number of different marine creatures. I found online that there are many types of mollusks that prey on other species by means of drilling through their shells. They use special mouthparts and enzymes to make the hole so that they can eat the soft parts of the snail or other mollusk. I also read that octopi can do the same. I found this on the website for the San Diego Natural History Museum: http://www.sdnhm.org/research/marine-inverts/marifaq.html I also read on line about boring sponges that create round holes in mollusks, I believe to live in them, here: http://www.seashell-collector.com/beginners/faq-f46/page_926.html. Finally, moon snails regularly feed on mollusks by using their radula to make a hole in the shell and feed on the soft parts of the mollusks. I found this information here, also at the San Diego Natural History Museum website: http://www.sdnhm.org/exhibits/mystery/fg_moonsnail.html.
Finally, in addition to the periwinkles in the water, we also found some snails on land, a grove snail. It was lighter because its shell was thinner, and their shells were more colorful. As opposed to the periwinkle, the grove snail had what looked like 4 antennae when it came out of its shell as opposed to the two on the periwinkle. There are two different kinds of grove snails, the white lipped snail Cepaea hortensis, and the brown lipped snail, Cepaea nemoralis. Usually they can be told by if their lip around the shell aperture is brown or white, but sometimes this is not the case. Otherwise, they can only be distinguished by dissection. I am not sure which type of grove snail the ones we found were, but in the picture it looks like both— one seems to have a brown lip and one has white. The two types of snails are found in similar habitats so this is far from impossible.
On the beach, we found five grove-snail shells all clustered by one rock on the beach. I believe this is because a bird uses that rock to drop the shells on, crack them open, and eat the insides.
Grove snails and the common periwinkle that we found in the tidepool look similar. In terms of classification, they are in the same kingdom (animalia), phylum (mollusca), and class (gastopoda). However, they differ when it comes to the next level of classification.
I really enjoyed our day at Lovell’s Island. I feel as if I am starting to see the bigger picture of marine life in Boston Harbor: how organisms interact with each other, how they are related, and how they can affect the surrounding environment. I look forward to our next class!
- Sabrina Liu