Monday, August 3, 2009

Assignment 3

Hi everyone! I'd like to start out by revisiting some things from our previous blog and make some changes/additions to my post. First off, while i still think the changes between this years barking crab observations and last years are due to increased rainfall, decreased salinity, and increased nutrient concentrations, i think the main impact of these changes is seen in the amount of brown algae present. In the picture from last year, there isn't as much brown algae compared to this year's observations. This is because the increased nutrient concentration from all the rain we have had this year is mainly affecting the algae, a primary producer in the ecosystem. I think that a significant increase in the amount of algae is detrimental to the growth of the other species we saw, such as mussels and tunicates, which is why there also seems to be more variation of organisms and larger mussels in the picture from last year. One way to test this theory would be to conduct a mesocosm experiment in a lab, with multiple tanks that mimic the environment at the barking crab as closely as possible but with variations in salinity and nuteirnt concentrations. This way, we could directly observe the effect that changes in salinity and nutrient concentrations would have on all the organisms present and specifically the growth of brown algae.

As for the mystery cheeto-like creature that i had previously identified as the reb beard sponge... I now think this is an orange or red sheath tunicate. It is thought that they got here from hitchiking on the bottom of boats from the Pacific, which is why they were not found in our guide books. They are an invasive species which tend to out-compete native organisms of Boston Harbor in brackish water conditions, which is why we saw most of them at the barking crab where fresh storm water is drained into the bay (1,2).

Now to move on to some observations made at Lovells Island. First, the common periwinkle. It seems to an accepted idea that the periwinkle is not entirely native to New England, both in our guide book and on the internet. It was originally from Western Europe, was brought to Novia Scotia, and has now migrated south to New England over 100 years ago. However, there does seem to be a debate about whether or not this invasive species is having a profound effect on the landscape in inhabits. One side beileves this species is completely harmless, the other thinks it is transforming sandy beaches into rocky beaches. There seems to be a lack of scientific study from both perspectives, however, so it is difficult to come to a solid conclusion one way or the other. I personally am leaning towards the idea that the periwinkle is causing a transformation of the North Atlantic seashore simply because i find it hard to believe that an invasive species would not have an effect at all on an enviroment that it is not native to. This idea just does not follow the trend we have been seeing for several years regarding the impact on most invasive species in all types of environments (3). I also think that their main predator in New England is probably the Northern Moon Snail. I am basing this off of the holes we saw in the shells of dead periwinkles that appeared to have been made by some sort of tiny drill. The moon snail feeds mainly on periwinkles and clams in the intertidal zone by drilling through the shells of its prey with its radula and digesting/sucking out the soft parts in the middle. In addition, the moon snail tends to bury itself deep within the sand of the intertidal zone, which is why we did not actually see any of them among the rocks and periwinkles (4). Since we saw these holes in both clam shells and periwinkle shells, and since the habitats of the two overlap extensively, i am pretty confident that the moon snail is to blame for the holes that we saw.

At the tide pool, we saw a lot of rockweed, periwinkles, barnacles, and algae, but the most amusing creature was a type of small crab, pictured below.

I believe this crab species is an asian shore crab, and invasive species originally from the Korean and Chinese coasts, based on its coloring, body shape, and agressive behavior. Though they try to put up a tough fight, they are pretty small and their claws do little damage, making them cute and fun to play with! I thought finding these was the best part of the Lovells Island trip.

The land snails we saw, pictured at the right, are likely to be a combination of two different species: the grove snail and the white-lipped snail. The snails with the lighter colored body are white-lipped, and the darker colored body ones are grove snails. Both species has a wide variety of shell colors, including those we observed on the island. They are indeed invasive, originally coming from Europe as the most common type of land snail there. They probably got there by hitchiking on shipments of plants or vegitables and have found the Sumac tree of New England to be a perfect habitat (5,6). My theory on how the snails ended up in a concenrtated area on the beach is tat Bruce put them there. However, if he had not, they could have easily been washed down to the beach from the Sumac trees and walls of the old forts inland on the island by rainfall, which on an island tends to drain to the ocean as it is in general the lowest level of elevation. The distribution of shell colors i think are due to the primary haibtat of a snail's gene pool. A snail that is found in dark colored tree bark will likely have more and thicker brown stripes on their shells to blend in with the brown color, snail found grazing in leafy greens will be some variation of yellow with thin brown stripes, and a snail found living within the walls of the forst will have a dull pinkish/brown color to blend in with the dirty walls and the surrounding soil of its habitat.

Overall, yesterday was incredibly fun and i had a great time!

See you all in class,
Sam Gifford


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