RESUMO
The intertidal zone is an especially stressful thermal habitat, typically exposing residents to air temperatures for up to 6 h at a time, twice daily. Tolerance to elevated temperatures has been particularly well-studied for a variety of intertidal species, especially with regard to upper thermal limits during summers. However, in recent years, as climates have been changing around the world, temperate zone intertidal organisms have sometimes been exposed to periods of unusually high air temperatures during the winter. The present study sought to examine the impact of elevated temperatures on survival and clearance rates of winter-acclimated intertidal individuals of the sedentary marine suspension-feeding gastropod Crepidula fornicata. Individuals were collected intertidally from Nahant, Massachusetts from late January to early April each year for 5 years, maintained in the laboratory at the acclimation temperature of 6 °C, and exposed in the laboratory for 3 h to temperatures as high as 37 °C in seawater either once or twice, 24 h apart. Although mean clearance rates were substantially reduced for at least the next 12-24 h after individuals were returned to the 6 °C control condition following exposures to elevated temperatures as low as 21-26 °C, we saw little mortality even following two 3 h exposures to 35 °C, or single exposures to 37 °C. Mortality was substantial, however, in one experiment following a double exposure to 37 °C. Smaller individuals (~5-12 mm in shell length) were somewhat more sensitive to the thermal stress than adults were. Intertidal members of C. fornicata in Massachusetts seem well-prepared to deal with the increasing range of winter air temperatures associated with the global climate confusion predicted for future years. Additional studies will be required to understand the physiological and biochemical mechanisms used by winter-acclimated individuals of this species to tolerate such periodic substantial temperature increases of 29-31 °C.
