Dogwhelks maintain predation on blue mussels across low tide durations and macroalgae cover

Abstract Environmental stress may modulate predator–prey interactions by altering predator performance and thereby the strength of top-down control. In intertidal systems, air exposure during low tide can alter predator activity and feeding patterns. We experimentally tested how air exposure and habitat complexity influence feeding by the dogwhelk Nucella lapillus on blue mussels ( Mytilus spp.) under natural temperature and light conditions during a summer to autumn transition on the west coast of Norway. Across 96 mesocosms, we manipulated low tide duration (0, 3, or 9 h) and macroalgae cover while tracking individual dogwhelk activity and consumption for nearly three months. Handling time (includes drilling and feeding) increased with mussel size following a power-law relationship, from 0.5 days for 10 mm mussels to about 20 days for 100 mm mussels, and was further increased by shell thickness. Macroalgae cover shortened handling time of large (57–73 mm) mussels by 22% but had no effect on small (17–33 mm) mussels. Prolonged air exposure (9 h) reduced proportion of prey-handling dogwhelks and total consumption relative to shorter exposure (3 h), despite leaving handling time unchanged. While cooler temperatures slightly shortened handling time (~ 4% per °C), they extended the complete cycle duration, from initiating handling of one mussel to initiating handling of the next, by roughly 10% per °C and decreased the proportion of prey-handling dogwhelks. Dogwhelks showed remarkable resilience, maintaining predation across all levels of air exposure, algae cover, and thermal regimes. This suggests that dogwhelks may be able to maximise energetic gains by choosing their vertical position in the intertidal zone according to beneficial microclimatic conditions, thus regulating their performance. Their locally persistent predation pressure may shape blue mussel populations in Norwegian waters, a widely distributed yet declining foundation species of major ecological importance in the Northern Hemisphere.