Poleward range contraction of a subantarctic limpet: weak larvae and strong adultsMacroecology

Spencer Virgin¹, David Schiel¹

¹University of Canterbury, New Zealand

Climate change and the increasing frequency of extreme climactic events have caused poleward range contractions of numerous species. Such range shifts in the intertidal zone are often caused by a combination of increased aerial and water temperatures, especially along coastlines with converging warm- and cold-water currents. This is the case on New Zealand’s South Island, where cooler and warmer water currents converge along the east coast. Relatively little biogeographic research has been done, however, on intertidal species in New Zealand, but museum records suggest that a common cold-water limpet species (Cellana strigilis) range has contracted substantially since the 1990s. In contrast, a closely related northern species (C. denticulata) with an overlapping southern distribution has maintained its distribution over the same period. To determine if and why the southern species contracted while the northern species remained, we sampled multiple sites along the coast, tested the thermal limits of adult limpets from both species, induced spawning and reared larvae to competency at a range of temperatures to determine larval thermal tolerance, and hindcasted adult limpet body temperatures using available meteorological data to determine if adult or larval thermal tolerances limited distributions. No C. strigilis were found near their historic northern range limit, suggesting a poleward range contraction of 350km. The northern species had higher adult and larval thermal tolerance than the southern species, and heat budget modelling indicated that the equatorial range limit of the southern species was more likely to be limited by larval thermal tolerance than adult thermal tolerance, which may explain how this species originally persisted at its northern range limit. This shows the importance of incorporating life history stages into determinations of species resilience, especially for intertidal organisms with pelagic larval stages that experience completely different conditions from adults.