Physiological responses of cooccurring intertidal limpets (Cellana spp.) to acute and repeated heat stress

Abstract

Limpets help maintain bare space and act as sentinel species of thermal stress in intertidal reef ecosystems. However, little is known about the physiological responses of New Zealand's widely distributed Cellana spp. limpets to thermal stress. We tested if there were differences in thermal tolerance in summer and winter and heat shock protein concentrations among four Cellana species that occupy different shore elevations. For one highly abundant species (C. denticulata), we tested whether thermal tolerance was affected by limpet size in summer and winter and whether thermal tolerance and oxygen consumption in air and water were affected by repeated heat stress. Limpet species from higher shore elevations did not always have higher breakpoint temperatures than those from lower elevations, potentially due to differences in homing behaviour. Similarly, there was no effect of size, season, or repeated heat stress on thermal tolerance. HSP70 concentrations were highest in C. denticulata, but were not affected by temperature (19–34 °C), indicating that limpets maintain high concentrations of constitutive HSP70. Limpets exposed to repeated heat stress in air had higher heart rates and oxygen consumption than those maintained at ambient temperature (19 °C). However, when both treatments were flooded with 18 °C seawater, heart rates were similar, but oxygen consumption was greater in the ambient treatment, indicating that non-stressed limpets may incur an oxygen debt during aerial exposure. This study provides new understanding about the effect of acute and repeated heat stress on the physiology of these conspicuous and abundant grazing invertebrates, which will help better predict their distributions in response to climate change.