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For years I tramped up and down the Maine shore, paying little heed to the creatures under the seaweed. It was whales that fascinated me when I was little. I was sure I wanted to grow up to research them, and I couldn't wait to get started. I had hopes that some day orcas would swim into my clam-flat cove—yet I soon learned that that was highly unlikely to happen in Maine. With a lack of whales at my beck and call, I soon turned to seals. They were almost accessible; however, they were still too large to fit into a tank in my backyard. With seals and orcas off the list, I became needy for my research fix. I racked my brain and took a walk to my little cove. No orcas, no seals. The tide was low, and the clam flat's odor filled the autumn air. The blue sky was crystal clear, and the rocks were still warm from the noon sun. I heaved a sigh and kicked off my sneakers. The ledge was warm and felt perfect under my toes. I ran barefoot along the rocks, jumping on stepping-stones across the mud flat to my island. I bent low and picked up one of my periwinkles. I hummed to it as I filled my lungs with the fresh air. Then the circuit was completed. The electricity ran as excitement through my veins. I scrambled back to ask my mom. After some careful rounds of negotiation, the proposed periwinkle laboratory was approved for immediate construction in my basement. It wasn't whales, but my research had begun.
Background Information On the northeastern coast of the United States and Canada there are several species of marine snails. Among the most studied are the rough periwinkle (L. saxatilis) and the smooth periwinkle (L. obtusata), but there are few studies in the Gulf of Maine on the common periwinkle (L. littorea). All these species can be found on the rocky intertidal shores of the Gulf of Maine and are easily identified by specific characteristics (Morris, 1951). |
 The common periwinkle shell (Littorina littorea). The common periwinkle (L. littorea) is one of the most abundant marine gastropods on the North Atlantic coast. It is an exotic species from Europe that was introduced accidentally to Nova Scotia around 1857. Its range has slowly spread south, displacing some other small snails. The current range of the common periwinkle is from the Bay of Fundy to New Jersey. Its range does not extend further south, likely due to the warmer waters and sandy substrate of those shores. The common periwinkle is approximately one-half inch to one inch in height, and is gray to black in color. The shell is fairly heavy, solid, and stout, with about six to seven whorls. It has a thick outer lip, is black on the inside of the aperture, and the tip of the spire is often white (Chenoweth and McGowan, 1993). Common periwinkles live in the intertidal zone (the area of the shore that has alternating periods of exposure to air and then water). Periwinkles distribute themselves in different positions on the shore. There is dramatic variation in the zonation of periwinkles. The distribution is not uniform along the intertidal zone and varies from site to site (Williams, 1964). Larval periwinkles disperse on the tide and float in the water column for several weeks. Gradually they grow a shell, transform into tiny periwinkles, and settle to the bottom of the subtidal zone. According to the literature, periwinkles then move up into the intertidal zone and become sexually mature within 18 months. During these months periwinkles can grow to be 18 millimeters in shell height. Most periwinkles live only two years, while some can live up to 10 years and grow to 37 millimeters (Chenoweth and McGowan, 1993). The common periwinkle plays a significant role in the ecology of the Maine shore. Periwinkles help to control the abundance of the algae community. Foraging by dense populations of periwinkles removes large quantities of green algae and loosens sediment from the substrate. This causes increased water flow over the shore bottom, washing sediment away and leaving exposed rocky shores (Chenoweth and McGowan, 1993). |
        
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