The Non-Lethal Effects of Climate Change on the Territoriality of Lottia gigantea

The intertidal zone has been described as ground zero for global warming. Here, the owl limpet, Lottia gigantea, adapted to the cool ocean temperatures, must withstand a few hours of baking sun during day-time low tides. This hardship is predicted to increase in frequency and severity in the future as the globe warms. Our research hypothesized that heat events compromise territorial behavior of L. gigantea. All observations and experiments were performed at Inspiration Point near Newport Beach, California. We measured the natural radiant temperature of tagged limpets during day-time low tides using a field-calibrated infrared “thermogun”. We also experimentally amplified radiant temperatures of limpets by 7-12°C using mirrors to reflect the sun’s heat. Control limpets were not heated. We then observed the behavior (Territorial, Retreat, or No Response) of the same limpets during high-low tide (0.5-0.6m ) when limpets were washed by the sea. Territorial encounters were staged by using “bait limpets” placed in the path of tested limpets to induce a response. We found that high radiant temperature is correlated with decreased movement, responsiveness, and aggressiveness of limpets. By contrast, experimental evidence of high temperatures reducing territoriality was weak, likely because of the short time span of heat amplification. Lottia gigantea is a bona fide “ecosystem engineer” whose territorial behavior shapes the rocky intertidal community of invertebrates. Our data show that local heat events compromise the territorial behavior of L. gigantea, which may consequently alter the rocky intertidal community

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