Nucella lamellosa

Lore & Background

Nucella lamellosa is a large snail with a strong shell, growing to a length of 100 mm and width of 50 mm. The shell has no more than seven whorls and a horny operculum. The spire is well developed, with a short notch to accommodate the siphon. This snail is rather variable in colour, shape and surface texture; some specimens are smooth, others rough, and others have frilled lamellae. Some of these features may be as a result of abrasion and wave action. When present, the spiral sculpture takes the form of one or two ridges per whorl, the whorls being flattened near their joints making them appear angled. The snail can be white, grey, brown or orange, occasionally purplish, and is sometimes spirally banded.

This whelk is a predator, feeding largely on mussels and barnacles. The radula is used to scrape through the shell of the prey and the soft tissue is extracted. The whelk is itself eaten by crabs such as the red rock crab Cancer productus and the seastar Pisaster ochraceus. In the presence of the crabs, there is a tendency for the whelk's shell to grow thicker and more robust, and thus less easy for the crab to crush. This may be as a result of chemicals released into the water by the crabs, because the thickness of the whelk's shell seems unaffected by the presence of Carcinus maenas, a recently introduced invasive species of crab that also feeds on whelks. A different response in shell morphology was evinced in the presence of the seastar: the shell tended to get longer with a high spire, enabling the whelk to retract its soft tissues as far as possible from the seastar. If both crabs and seastars were present, the shell phenotype that tended to evolve reflected the response to the predator that caused the greatest mortality. The whelks also show behavioural responses to both crabs and seastars by seeking refuge.

Breeding takes place in hidden locations such as under rocks, with many whelks congregating to mate and lay eggs in capsules which resemble clusters of oats as they dangle from the substrate.

Reader's Guide

Nucella lamellosa is one of the commonest whelks in the intertidal zone of the Pacific Northwest, found from the Bering Strait and Aleutian Islands to central California. Its significance lies in its role as a predator of mussels and barnacles, shaping the intertidal community. The species is notable for its phenotypic plasticity in response to predators: shell thickness increases in the presence of crushing crabs like Cancer productus, while shell length and spire height increase in the presence of the seastar Pisaster ochraceus. These induced defenses appear to be mediated by chemical cues from the predators, as the invasive crab Carcinus maenas does not trigger the same thickening response. When both predators are present, the shell morphology that evolves reflects the predator causing the greatest mortality. The whelk also exhibits behavioral responses, seeking refuge from both crabs and seastars. Its variable shell morphology—smooth, rough, or frilled—may partly result from abrasion and wave action. Breeding aggregations under rocks produce egg capsules that resemble clusters of oats, a distinctive reproductive strategy. The species thus serves as a model for understanding predator-prey coevolution and inducible defenses in marine gastropods.

Did You Know?

• Its shell may grow thicker in the presence of the crab Cancer productus, possibly due to chemical cues.
• The egg capsules of this whelk resemble clusters of oats dangling from the substrate.