Field Experiments Demonstrate that Heat Spells Can Reduce Territory Defense in the Owl Limpet, Lottia gigantea

The intertidal zone may provide insights into how global climate change will impact natural ecosystems because its inhabitants are so vulnerable to heat stress during daytime low tides. The territorial limpet, Lottia gigantea, significantly changes the mid to high intertidal landscape by removing sessile organisms (barnacles, mussels, coralline algae), removing or redistributing gastropod grazers (snails and limpets), and encouraging the growth of micro-algae. We measured temperature and behavior to ask whether heat spells impede territorial behavior. During daytime low tides we artificially heated tagged limpets (25-35°C, vs. 15-24°C in unheated control limpets) in a shaded habitat and returned during the evening high-low tide to test for movement and territorialism. Only 25% of experimentally heated limpets moved during subsequent evenings, while 70% of nearby unheated control limpets moved during the same observation period (Fisher’s exact test, P = 0.015). Correlations of territorial behavior and the temperature of those territories showed limpets in warm microhabitats moved less and were less aggressive than those in cool habitats. Together, these observations support the ideas that the territorial impact of L. gigantea is compromised after intense heat spells, and non-lethal effects of heat spells may reduce their impact on the intertidal community