Reduced tenacity during “high-speed” territorial encounters in the intertidal owl limpet, Lottia gigantea: Agonistic escalation increases risk of wash-off

Abstract

The dislodging effect of breaking waves is among the critically important factors structuring rocky intertidal communities. Because behavior is so difficult to study in the field, the interaction of wave force with behavior of intertidal organisms is poorly understood. Here, we present a field study of the interaction of breaking waves with the natural behavior of individuals of Lottia gigantea, an intertidal limpet with a complex territorial behavioral ecology. We hypothesized that limpets engaging in fast-moving territorial chase in response to intraspecific contact are more vulnerable to wash-off by a passing wave than are slowly foraging limpets that do not take part in such chase. We measured the lift force required to dislodge limpets while they were engaged in three natural behavioral responses to intraspecific contact in the field: 1.) continued foraging, 2.) retreat, and 3.) territorial pursuit. We divided the measured force-to-remove by aperture area to estimate resistance to wave-induced lift force, or tenacity. Tenacity (Newtons·cm−2) in slowly foraging limpets was 2–4 times stronger than previously reported for moving limpets (retreating at high speed from sea stars). Small foraging limpets showed stronger tenacity than did large limpets. Tenacity was significantly reduced by high-speed territorial and retreat responses, especially in small limpets. We compounded the wash-off probabilities of tenacity during the expected number of high-speed chases in the face of an entire year of reported waves at a nearby ocean buoy, and estimated that limpets should suffer substantially greater mortality (11.5%) than do limpets that refrain from all territorial chase (2.9%). Overall, these data support our hypothesis that dislodgement by breaking waves comprises a significant risk attendant to territorial chase. The fact that limpets nevertheless engage in these chases suggests that the resources gained by this behavior are substantial.