An intertidal snail shows a dramatic size increase over the past century

Area of Science:

• Marine Biology
• Evolutionary Ecology
• Malacology

Background:

• Predation pressure, such as from invasive crabs like Carcinus maenas, can drive changes in marine snail shell morphology.
• Previous studies in the Northwest Atlantic reported shorter, thicker shells in response to crab predation.
• The long-term evolutionary responses of marine snail shell architecture to historical environmental changes are not fully understood.

Purpose of the Study:

• To investigate the long-term changes in shell length and thickness of Nucella lapillus over the past century.
• To assess the influence of environmental factors, such as wave exposure, on these morphological changes.
• To understand the broader implications of altered shell morphology for North Atlantic marine ecosystems.

Main Methods:

• Comparison of archived Nucella lapillus shells collected between 1915-1922 with shells from the same sites collected in 2007.
• Measurement of shell length and thickness, with adjustments for shell length to analyze independent thickening.
• Analysis of shell morphology changes in relation to wave exposure data from collection sites.

Main Results:

• Nucella lapillus shell lengths increased by an average of 22.6% over the past century.
• No significant shell thickening was observed after correcting for shell length.
• The greatest increases in shell length occurred on sheltered shores, indicating an interaction with wave exposure.

Conclusions:

• Contrary to expectations, Nucella lapillus shell length has increased, not decreased, in response to historical environmental changes.
• Wave exposure significantly interacts with temporal changes in shell morphology.
• The underappreciated impacts of historical morphological trait changes on marine ecosystems highlight the need for further research.