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Dogwhelk shell size sees dramatic increase in less than a century

Dogwhelk snails (<em>N. lapillus</em>) feeding on barnacles (<em>S. balanoides</em>)

Three dogwhelk snails (Nucella lapillus) feed on barnacles (Semibalanus balanoides) along a rocky intertidal shore in Maine.

Comparison of dogwhelk shells from early 20th century museum collections (archived at the Academy of Natural Sciences of Philadelphia) and the same 19 coastal locations resampled in 2007 revealed ~23 percent longer shells in the recent period, although there was no evidence of changes in other shell characteristics. This finding accounts for changes in shell thickness and shape reported previously, contrasts historical size declines reported for other marine species, and has implications for this snail as both predator and prey.

This research, which focused on dogwhelk snails living in the northwest Atlantic Ocean around Mount Desert Island, Maine, was conducted by a team of biologists at the University of Pennsylvania, who completed a research study that began in 1915. The dramatic increase in the size of the snails' shells in less than a century provides a clear illustration of how fast and effectively change can occur. The Penn teams results demonstrate that monitoring changes in shell morphology requires careful accounting of variation in local conditions, such as wave exposure, which can affect not only shell shape but also size.

Possible explanations for this increase in shell size are a reduction in the last century in the size and number of native predators of dogwhelks in the Gulf of Maine; increases in ocean temperatures, which could have lowered mortality and increased growth, both of which would cause an increase in size; and the arrival of new predators as invasive species could have selected for larger body size. The researchers hypothesize that the dramatic increase in size may give the snail an edge when preying on large mussels and barnacles, while protecting it from predators like crabs.

The study was supported in part by a grant from the National Science Foundation.

To read more about this study, see the Penn news story Penn biologists demonstrate that size matters in snail shells. (Date of Image: June 2005)

Credit: Jonathan A. D. Fisher

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