Resistance to crushing from wave-borne debris in the barnacle Balanus glandula

Barnacles of the same species (Balanus glandula ) show differences both in shell morphology and in their ability to resist crushing from impact at two sites within 8 km of each other which differ in their natural exposure to wave-borne debris (Cattle Point and False Bay, San Juan Island, Washington, USA). In studies performed in 1987, barnacles with shells of a given base diameter at the site exposed to more impact (Cattle Point) were found to have smaller bodies, shorter and thicker shells, and a more protected placement of their opercular valves than barnacles at the protected site. When tested with a standard impact, barnacles from the exposed site were more resistant to crushing both on the first impact and (for those surviving that test) on a second impact 2 wk later. The morphological differences between the two populations may be due to a combination of different shell: body growth rate ratios at the two sites plus passive remodelling of the exposed barnacles by small impacts.