Fisher, J., Rhile, E., Liu, H., & Petraitis, P. (2009). An intertidal snail shows a dramatic size increase over the past century Proceedings of the National Academy of Sciences, 106: 5209-5212 DOI: 10.1073/pnas.0812137106
Nucella lapillus is an intertidal snail commonly found on the rocky coasts of the North Atlantic. In North America, it lives along the east coast north of Long Island.
Fisher et al. have discovered that between 1915-1922 and 2007, the shell length of N. lapillus at 19 sites around Mount Desert Island, Maine increased by an average of 22.6%.
Comparison of shell sizes of N. lapillus from 19 sites. The 1:1 line is the line about which the points would scatter if there had been no change in shell sizes. Fig.1 from Fisher et al.
Shell sizes of this species are significantly influenced by exposure: snails living in areas exposed to waves are in general smaller than those living in sheltered areas, because it is easier for larger snails to get dislodged by waves. The data in this paper (see the figure above) show that the increase in shell length was greatest at the wave-sheltered sites and smallest at the wave-exposed sites.
The reasons for the size increase of these snails are not known at the present. The possible factors include predation by the crab Carcinus maenas, increase in sea water temperatures and a long-term increase in nutrients.
The 1915-1922 collections were done by Harold S. Colton and are currently kept at the Academy of Natural Sciences of Philadelphia. The present study demonstrates the value of properly collected (with locality data) and curated specimens in research that may sometimes take place decades after the collections were done.