Lovell's island

Again, another beautiful and educational day on the boston harbor. Before I get into my post or do any research I would like to submit my hypotheses for the hole in the sea shell "mystery." I actually sat back and really racked my brain trying to think of different possibilities.

Question: how were the holes in the sea shells made (for simplicity sake I am going to assume everything we saw was a mollusk or mollusk like creature)?

Hyp1: My initial thought when professor Berman first asked the question was "birds", probably because my background in biology has programmed my mind to reduce all topics to the "origin of life" and Darwin's study of those dang finches. In this case, I thought maybe birds on these coastal islands might have developed beaks that were strong enough to penetrate the shells of mollusks exposed during low tide. But that doesn't seem very feasible physically or biologically because 1) it would be hard for a bird to hold a mollusk still to create such a uniform hole 2) it would probably require an intense amount of effort for such a small reward. But not out of the realm of possibility.

I began thinking about ways that holes are made in any substance. My first inclination was, understandably, "force." I have a linear and logical mind and if someone asked me to make a hole in something I would first think about using force. The only other two methods I could come up with were "chemical degradation" and "erosion" (which can be physical or chemical).

Hyp 2: chemically) maybe there are organisms that are able to concentration a corrosivesubstance onto the shell to create the hole. This process would be tedious and long so it would need to be able to establish a connection with the other shell for an extended period of time. It would also need a purpose which could be either symbiotic, parasitic, or predatory. Among my observations yesterday were mollusks living on top of other mollusks (e.g. lady slippers).

parasitic mollusk hyp: The holes we observed in the shells of the mollusks could have been made by other mollusks (perhaps single sided) that grew on top of it and chemically burrowed a hole into the hosts' shell. The relationship would be parasitic because the "invaders" sole purpose would be to steal food from its host to minimize energy exersion. That way once it creates the hole it in never has to worry about food again until its host dies.

predatory macro- and micro-organism hyp: There are many examples of micro-organisms in extreme habitats that have evolved to sustain themselves on modest diets (e.g. bacteria in caves that actually eat "dirt"). Maybe there are organisms in the ocean that are able to process and digest the mollusk shell for sustenance. With that said maybe there are larger organisms which are able to drill or chemically degrade a hole into the mollusk and actually eat them. Personally, that makes the most sense to me.

erosion: maybe "not all shells are created equal" and some have weak spots that erode after the mollusk has died by: 1) current continually washing it over with sand 2) the p.H. of the water 3) foreign chemicals etc.

hyp 3: THEORY OF EVOLUTION: Maybe the holes are actually a biological adaption that are beneficial in some way. Maybe it gives toxins a way to escape or prey another way in.

Investigation: I began with a general search about mollusks using the website www.marinebio.org "Familiar mollusks include oysters, chitons, clams, snails, slugs, octopus, and squid. Most mollusks have a soft body and a hard or “calcareous” shell... With a few exceptions, all living species of mollusks are categorized underGastropoda or Bivalvia. Another important class is Cephalopoda... Some scientists have determined that there is more biomass from marine mollusks than any other animal on earth... Mollusks reproduce through external fertilization where the eggs and sperm are released into the water. In some more complex mollusks, fertilization can take place internally after long courtship rituals and mollusk dances. Many of the more sophisticated snails are hermaphroditic. Some go through phases where they alternate gender, others are both female and male at the same time." Although informative it did little to lead me to a conclusion about the holes that are found in some of the shells so I googled "shells in the holes of mollusks" which led me to a www.wikiAnswers.com post (which was probably answered by professor Berman) which explained that it depended on the type of mollusk. Some mollusks (in the post it mentions abalone and keyhole limpits) developed the holes to aid in water circulation and respiration. Other mollusks are preyed upon by creatures like moon snails and oyster drills which create the hole and extract the creature from the inside to eat it. So not trusting this information for face value I used the examples provided in the post to look up keyhole limpets, moon snails, and oyster drills.

Keyhole limpets: I cross referenced the definition of a keyhole limpet with several sources (including but not limited to wikipedia, marinebio.org, peterson, etc.) They reside in the intertiday zone, can grow to be 4 inches in length and are generally not found north of the chesapeake bay. They have a flattened conical shape with dark radial lines with an opening which extends a muscular foot that holds onto rocks. The keyhole limpet is named for its central opening, through which respiratory currents pass.

Moon shell [snails]: (From peterson), found from the mass bay to the gulf of mexico. They have a glossy outer shell with a conical design and pictures (above) remind me of the great giant pink sea snail from dr. dolittle. Most importantly, "they are predatory on other mollusks, which they drill neatly, making a beveled hole."

oyster drills: (from peterson), they look like small conch shells and can range from 1in-2in depending on what part of the Atlantic it's found (range=cape cod-florida). "This major pest of oysters commonly destroys 60% or more of the seed crop in parts of the L.I. sound and lower Chesapeake Bat. Reduced salinity protects seed ground in fresher parts of tidewaters. The drill bores a neat hole in the oyster's shell and sucks out the soft part of the oyster."

In conclusion, there are two main ways that mollusks can have a hole in there shell. One is an evolutionary that helps the create breath better. The second is when a predator bores a hole in the outer shell to gain access to the flesh underneath. I would guess that the shells that we saw on Lovell's were bored by an organism like the moon shell.

I guess since I still haven't touched upon my experience yesterday I might as well delve into the second hypothesis situation

From Snails to Snail: comparing the sea and terrestrial snail

The only 3 distinct hypothesis I think I can make are: 1) Sea snails and land snails have different respiratory systems and 2) they have extremely different diets. We observed land snails eating vegetation so I will assume they are herbivoes and my research from above supports that sea snails can be herbivores or carnivores (maybe even omnivores). 3) from the anatomy we observed by coaxing our periwinkle out of its shell and collecting the land snails, there was a difference in the number of appendages. The sea snails had 2 and the land snails had 4


Land snails: (from http://lhsfoss.org/fossweb/teachers/materials/plantanimal/landsnails.html) Both sea and land snails are part of a class of the phylum mollusk called "gastropods" which is derived from the latin "gastro" - stomach and "pod" - foot. I was suprised to learn that slugs were in the same class as snails, although it makes sense; they are just a snail without the shell. Most land snails are hermaphroditic but they still have to mate to fertalize each others eggs. They are herbivores and anyone who has a garden knows they love green leafy vegetables. Their bodies are moisture sensitive and they need to maintain a certain degree of internal moisture to survive, although it doesn't take much because it has an internal supply do draw from called. If they do not receive enough moisture during a given period of time they will create a thick film which seals their aperture until more moisture is available. The land snail contains 2 sets of tentacles, a long set on the top of their head and a shorter set near their mouth (radula). The longer set is for sensing light but they lack pictural vision. The smaller set is for smelling, tasting, feeling, etc. for food or to sense other danger. "Snails breathe by taking air into a visceral cavity that is richly supplied with blood vessels—the snail’s version of a lung. When the snail extends from the shell, the access pore can be seen opening and closing just below the margin of the shell on one side. Also, the snail’s heart can be seen pumping blood by placing a snail on the lens of a flashlight and carefully looking through the translucent shell." The two varietals that we encountered most were the brown and white lipped grove snails (according to pearl).

Sea Snails: from peterson, sea snails are the most diverse class of mollusk with a huge variety of forms. For the most part the sea and land snails share most of their anatomy in common except for the fact that some sea snails breath through gills and they have separate sexes. And even those differences are not close to being 100% accurate in all circumstances. Sea snails also have 4 tentacles. Some sea snails have both lungs and gills. The real answer is that differences are vastly different from species to species of snail. There are snails that spend most of their time in the water but don't have gills and need to be above the water to breath. The wealth of information on this subject is incredibly confusing and doesn't seem to make very many certain distinctions that hold true in all cases.

My day at Lovell's:
-lesson 1: no matter how calloused the sole of your foot is, there is something sharp enough and long enough to penetrate it.

Lesson 2: Pearl was awesome and waaaaaaay into snails (maybe too much so).

Lesson 3: Bruce knows everybody (or at least who they are) east of the financial district.

Lesson 4: You can see so much life if you just look closer.

Lesson 5: don't be afraid to touch smell and in some cases taste.

So I had an awesome day on sunday picking crabs up out of the tide pools, squeezing sea squirts, bothering filter feeders and re-learning about barnacles...

Conditions:
time: 11-2:15
temp- upper 80's
sky- mostly sunny
humidity - low
tide (during time in tide pools) - at first going out then coming in
water clarity (1 being no visibility - 10 being crystal clear): 9
water temp: differed from pool to pool depending upon how long it had been disconnected from the open ocean and how much water was inside of it (comment on this later).
tide pool ground: "crumbly"

Observations:
- Emily, Alex and I actually went out of the tide pools into the open water to see if there were differences in the two environments. From what I could see there was not as much biodiversity in the open water as there was in the tide pools. The barnacles (which I believe consisted mostly of Northern Rock Barnacles) were more "active" in the open water than those in the tide pools which was an observation I felt viscerally. They were open and probably feeding on the content that the waves were sending over them.

-The floor of the tide pools themselves was rocky and mostly cobble. The tide pools also seemed to be a mollusk grave yard with so many empty shells everywhere. I probably devastated a small colony of perwinkles on my own which seem to blanket areas of the pools (may they rest in peace). To say they were the most abundant type of metabotropic marine life we saw would be an understatement. Maybe they might have battled the blue shelled mussels for that crown but I’m inclined to give it snails because they are more bad-ass.

-My favorite pool was the one closest to the open water and the farthest away from the first pool we went into. In that pool I saw noticeably more empty crab shells which would indicate seagulls preferred to drop them close to that pool. But what really caught my attention in that pool was a couple of large rocks, almost small boulders which had an identical makeup to the floats at the barking crab. The only difference is that the marine life on the rocks was more abundant, “livelier,” and bigger. There was sea lettuce, ladies slippers, filter feeders, golden star tunicate, moon shells, perwinkles, blue shelled muscles, sea squirts, a reddish furry sea weed, orange sheeth tunicate (or possibly red bearded sponge but unlikely according to Peterson), etc. etc. All this was on one rock. I wish I had the guts to bring my camera out with me, but sadly I didn’t get a picture of a filter feeder totally enveloped by tunicate. One of my favorite things I observed and played with was a small red furry sea weed which is so aptly named Brushy Red Weed. It’s found from the L.I. sound to Newfoundland. It’s found in tide pools or subtidal, usually perennial, dying back in winter in some places.

Andrew R. Comenzo