The Ecology of Lough Ine. XV. The Ecological Significance of Shell and Body Forms in Nucella

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Abstract
Two types of Nucella lapillus are described. A form from the open Atlantic coast in South West Ireland had a wider shell aperture, a more lightly constructed shell, a heavier body, a larger foot, and a tighter grip to the substrate than the form found in Lough Ine, a marine Lough connected to the sea. Tests in which both forms were placed with crabs in cages showed that the Nucella from the open coast were more susceptible to predation than those from Lough Ine; on the other hand, they showed greater powers of adhesion when attached to a slate and exposed to moving water. Experiments in the field confirmed that the open coast form succumbed to predation when transplanted into places sheltered from wave action, and that the Lough form was unable to maintain its foothold when moved to the open coast. It is concluded that two strong selective influences - wave action and predation - favor and probably completely account for the distribution of the two types of Nucella in the region studied.

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