For slow-moving rocky intertidal predators such as whelks, frequent stress can be detrimental. Most studies on the foraging behavior of whelks have been conducted in regions where tidal amplitude is > 1 m and on relatively small species. We studied the effects of wave action, desiccation, and water temperature on the foraging behavior of a large (approximately 80 mm) rocky shore whelk, Stramonita haemastoma, at the small-tide (< 40 cm) but wave-exposed Israeli Mediterranean coast. We hypothesized that in such conditions foraging activity of this large predator will be greatly limited. Field observations show that when wave height exceeds 0.5 m, activity of whelks decreases by at least threefold relative to that seen under calm-sea conditions, and most whelks remain inside shelters. Wave height data from offshore moorings demonstrate that such conditions occur along the coast >85% of the time. Whelks move into shelters or completely disappear when exposed to prolonged desiccation conditions that can last for days along the shore during spring and autumn. Foraging activity is greater at night than in daytime and might be related to lighter winds and calmer sea conditions at night. Laboratory experiments show that elevated water temperatures during winter do not result in increased predation rates relative to those measured during spring. This indicates that a seasonal endogenous biological rhythm may exist. Our findings demonstrate that the foraging activity of large whelks can be extremely constrained by high rates of disturbance, that is, frequent wave action, and less frequent desiccation. We claim that high rates of disturbance in the eastern Mediterranean explain why large whelks are scarce in intertidal habitats where food is plentiful but suitable shelter is rare.
Bibliographical noteFunding Information:
Acknowledgements We thank M. Gershon, T. Yacobovitch, and N. Sharon for assistance in the laboratory experiments. We are grateful to G. Piniak and an anonymous reviewer for their useful comments on an earlier version of this manuscript. N. Paz is acknowledged for editorial assistance. We also thank the Akhziv Field School for accommodating us, and the Nature Reserves Authority for the permit to work in the nature reserves and collect animals for experiments. This research was supported by Tel-Aviv University. The experiments comply with the current laws of Israel.
ASJC Scopus subject areas
- Ecology, Evolution, Behavior and Systematics
- Aquatic Science