Nucella lapillus (Atlantic Dogwhelk) deposits egg capsules on solid, intertidal substrates across the North Atlantic. This study investigated whether regional geographic variation or local wave-exposure affect the size of Dogwhelk egg capsules. Over 3 years, we evaluated whether Dogwhelks from wave-exposed and wave-protected sites in Massachusetts and mid-coast Maine differed in their egg-capsule size. Our results indicate that egg capsules collected from wave-exposed sites in Maine were smaller than egg capsules from wave-protected sites in Maine, but the size of egg capsules from Massachusetts did not vary with wave-exposure. These patterns in egg-capsule size coincide with Dogwhelk size from the same sites. Despite the positive correlation between the sizes of adult Dogwhelks and the egg capsules collected, wave-protected Dogwhelks from Massachusetts showed plasticity in the size of egg capsules produced but those from Maine did not. The Massachusetts Dogwhelk's greater plasticity in egg-capsule size highlights important local variation in control of reproductive investment and may accommodate fluctuations in desiccation stress and future climate change.