Snail shells increase dramatically in size in less than 100 years

March 28th, 2009 - 4:37 pm ICT by ANI  

Washington, March 28 (ANI): A long-term research has concluded that the shell of a particular snail has dramatically increased in size, during less than a century, thus providing a clear illustration of how fast and effectively change can occur.

The research, which began in 1915, was completed by a team of biologists at the University of Pennsylvania.

It determined that a snail making its home in the northwest Atlantic Ocean around Mount Desert Island, has experienced a dramatic increase in the size of its shell during less than a century.

The most striking finding, which has not been reported previously in Nucella lapillus, the Atlantic dogwhelk, is that shell length increased at all 19 sites where samples were taken.

Shell lengths of N. lapillus increased by an average of 22.6 percent during the past century, with no evidence of changes in other shell characteristics.

The Penn team’s 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.

Within the last century, the Gulf of Maine has experienced reductions in the size and abundance of native predators of dogwhelks, increases in ocean temperatures and invasions of new predators, and all three factors could have played a role.

Overfishing of native predators of dogwhelks, such as fish, and increases in temperatures could have lowered mortality and increased growth, both of which would cause an increase in size.

Also, arrival of new predators as invasive species could have selected for larger body size.

Changes in the shell architecture of marine snails enhance defenses and greatly improve survival against predators.

Stouter and thicker shells have been reported for N. lapillus and several other species following the introduction of predatory Carcinus maenas crabs early in the 20th century.

According to researchers, when the snails are exposed to crab cues, shells of small snails first thicken and then, once defended against shell-crushing predators, grow in length to a size beyond the abilities of the crab.

The dramatic increase in size, the researchers hypothesize, may give the snail an edge when preying on large mussels and barnacles, while protecting them from predators like crabs. (ANI)

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