Ontogenetic shifts and interspecies variation in tolerance to desiccation and heat at the early benthic phase of six intertidal invertebrates

During the early benthic phase of intertidal invertebrates, desiccation and elevated temperature are increasingly recognized as the most significant stressors, but it is not known whether all species are equally sensitive during this phase. In this study, involving 6 co-occurring rocky intertidal species (Nucella ostrina, Littorina scutulata, Mytilus trossulus, Chthamalus dalli, Balanus glandula, Petrolisthes cinctipes), we examined interspecific variation in (1) tolerance to desiccation and temperature at the early benthic phase and (2) the magnitude of ontogenetic shifts in tolerance. Ontogenetic shifts in temperature tolerance were significant but modest, whereas desiccation tolerance thresholds changed considerably throughout ontogeny in all species, and shifts were greatest in species that changed microhabitats during ontogeny. Tolerance at the early benthic phase also varied markedly among species; temperature tolerance thresholds ranged from 32.3 to 45.8°C, and juveniles were able to survive exposure to desiccation for durations ranging from 10 min to 29 h. Ontogenetic shifts in desiccation tolerance were largely ex plained by differences in body mass; thus individuals achieve increased tolerance through growth. However, variation among species was unrelated to body mass; rather, interspecific variation in tolerance thresholds of the early benthic phase was related to the upper limit of intertidal distribution of the species and to microhabitat use during this phase. The study revealed desiccation to be a greater threat to early benthic phase individuals than temperature in all species, but also discovered considerable interspecific differences in tolerance thresholds, such that species are likely to respond differently to present and future extremes in desiccation and temperature.