Role of sequential low-tide-period conditions on the thermal physiology of summer and winter laboratory-acclimated fingered limpets, Lottia digitalis

The rocky intertidal zone is among one of the most highly variable environments on Earth, with rapid and unpredictable changes in temperature on a daily basis. Numerous studies have investigated the thermal physiology of intertidal animals; however, few have focused on an organism’s capacity to withstand repeated heat stress during the emersion of low-tide periods and how previous exposures to sublethal increases in temperature may modulate the capacity to withstand severe heat stress. Lottia digitalis, a species of limpet ubiquitous along the Pacific coast of North America, were acclimated under ambient ocean conditions in the laboratory during the summer and winter months. Limpets were aerially exposed with or without preliminary heat exposures of varying magnitudes (15–35 °C for 2 h) the day before being challenged to a lethal temperature increase to investigate how sequential low-tide-period conditions affect upper thermal tolerance and temperature sensitivity. Limpets with a preliminary aerial exposure of 25–35 °C (summer) and 20 °C (winter) had greater upper critical thermal limits of cardiac performance as determined by final breakpoint temperature (~1.5–6 °C increase) and flatline temperature (~1–2 °C increase) than limpets with no previous exposure. The magnitude of temperature increase that conferred significant increases in thermal tolerance differed in summer and winter, reflecting seasonal differences in the thermal environment in nature. Fingered limpets’ upper thermal tolerance is plastic and likely modulated by the previous day’s low-tide exposure, demonstrating the importance of incorporating the repeated nature of stress into thermal physiology research in intertidal organisms