Amid the Rockweeds and Periwinkles Jenna Crovo
I close my eyes and gulp in the warm sea breeze. The soothing familiar aroma of the sea fills my nostrils, and another gentle wind teases my hair. A perfect Maine summer day, the clear azure sky stretches on for eternity as the sun's rays caress my slightly tan skin. Looking out across Penobscot Bay there is nothing but the blue-green, plankton rich water speckled with some of the islands that dot along the entire coast. My eyes then revert back to where I am standing, on a small rocky outcrop that drops down into a series of tide pools that are exposed at low tide. The more interesting and larger pools are closer to the water's edge; to reach them I have to cross a fair sized area of rocks covered in a species of seaweed. “Squelch” as my feet leave the rocky shore and onto the vast plain of rockweed. Fucus distichus, commonly known as rockweed, is frequently found on the shores of Maine where it attaches itself to rocks in the tidal zone. Like all seaweeds, rockweed attaches its holdfast to a single point on a rock and branches out dark olive colored plumes that can be several feet long. This particular species also has small air filled bladders that act as flotation devices to keep the rockweed close to the water's surface, a helpful adaptation to facilitate photosynthesis. Normally, the entire area with rockweed would be underwater, but this is low tide, exposing it to the earth's atmosphere. There is a specific technique when it comes to walking on rockweed infested rocks: never step between two rocks, always walk on the top of them. If I should fall while having my foot in a crevice, it could result in a sprained ankle. Taking this into account, I gingerly step from rock to rock, trying to maintain my balance. Suddenly, my hiking boot loses its grip as I fall backwards, catching myself with my left hand. Upon contact, the rockweed is slippery and rubbery to the touch, as expected. Muttering a few choice words under my breath, I regain my posture like an ungainly newborn foal, wobbling forward and backward until I attain a center of gravity. I pause a moment before continuing on my expedition and crouch down closer to the rockweed. Grabbing a huge clump in my hand, I pull the seaweed back to reveal a tiny rock crab, Cancer irroratus. Now, rock crabs, unlike the larger brilliant blue Maryland crabs, are ugly little beasts. They are a mottled greenish brown color, and their shell is rounder in shape, lacking the protective spines of the Maryland crabs. The crab does not scurry away; rather it sits unmoving on the rock, probably wondering where its cool moist covering went. I carefully replace the rockweed to its original position and continue my trek to the tide pools. A few more minutes of traversing over the rockweed and I have reached the pools where marine life abounds. I quickly notice the myriad of periwinkles, Littorina sp. that cling to the wet rocks around the pools. Their spiral-like shells are a deep brown and slightly larger than my thumb nail. Many people tend to describe them as snail-like because of their single pseudopod and two eye stalks that project from the shell. Many say that a periwinkle will come out of its shell if one hums to it. Eager to test the myth, I pry one of the mollusks off of a rock, which does take some effort; its pseudopod anchors the periwinkle firmly to the rock. I look into the aperture of the shell and notice that the shutter-like operculum has closed, protecting the soft invertebrate inside. Bending my head down slightly I begin to hum, keeping the sound at a low constant note for several minutes. The periwinkle does actually come out, slowly extending one eye stalk, and then another. The pseudopod also becomes visible as the operculum contracts more. After seeing that the periwinkle does indeed come out of its shell when it is hummed at, I gently place it back on the rock where it was initially. While the periwinkles are certainly present in large numbers, there are also other organisms to be found. In addition to the periwinkles, there are also sea stars and sea anemones. The sea stars can be seen as I look into one of the largest tide pools near the water's edge. The ones here are on the small side, exhibit the classic pentameral symmetry, and could easily fit into the palm of my hand. They are easy to see as they are a chalk white, and clearly stand out against the rocky bottom of the shallow pool. This color does not seem to be a favorable adaptation in the eyes of natural selection. The echinoderms could easily be spotted by a predator such as a herring gull, scavenging for food. I continue to ponder this conundrum as I reach my hand into the pool; the cold salt water washes over my skin as I remove one of the closer sea stars. The little echinoderm moves slowly in my wet palm, stiff and bumpy to the touch. Its texture actually gives the organism the classification of echinoderm, which means “spiny skin”. The slow movement of sea stars comes from an extension of the characteristic water vascular system that allows them to move. I believe I have harassed the tiny invertebrate enough and place it back into the water. Sea stars are relatively common in tide pools, but sea anemones are slightly harder to come by. Of all of the organisms that can be found at tide pools, sea anemones have to be some of the more exotic creatures. To find them I need to search the tide pool more extensively. Therefore, I discard both my hiking boots and socks and step into the pool. The water is still quite frigid, even in June. Luckily the water will not come up further than my knees; this pool is on the shallow side. As I walk further in I create little ripples that undulate across the water's surface. I look down while I am walking for two reasons: I do not want to cut myself on the broken mussel shells that are commonly strewn here, and I am determined to find a sea anemone. After a few more steps I come to a cluster of large rocks, barely submerged under the water that is now lapping my knees. I search around the rocks and find what I am pursuing. Nestled at the base of one of the rocks are two small frilled anemones, Metridium senile, exquisite animals. Like all anemones, they attach themselves firmly to a rock via their pedal disk. The frilled anemones have a smooth dark brown column with a crown of fine coffee colored tentacles at the anterior end. The tentacles appear to be several centimeters long and gracefully sway back and forth in the water. While the tentacles may seem to be an aesthetic accompaniment, they are the weapons used in protection and feeding. When touched, they release microscopic barbs that function as hypodermic needles. The barbs release venom that numbs the victim so that it may be consumed or stopped from threatening the anemone. A Homo sapiens could even feel the effect of the compound. To test this, and being fully aware of what would happen, I stroke a few of the tentacles with the tip of my pointer finger. They feel quite soft, and somewhat slimy, but it does not take long before my finger is indeed numb. Having discovered my subject, I turn to make my way back to my neglected boots and socks; I really should return to civilization. My watch tells me that I have been at the pools for almost two hours, and I am at risk of developing thymine dimers, which can cause skin carcinoma, from too much exposure to the sun. Once again I cross the rockweed plain, being careful not to step between the rocks, leaving the periwinkles and anemones to welcome the awaiting high tide.
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