SUMMARY

The shrimp Rimicaris exoculata swarms around hydrothermal black smoker chimneys at most vent sites along the Mid-Atlantic Ridge. This species maintains close proximity to the hydrothermal fluid, where temperatures can reach 350°C and steep thermal and chemical gradients are expected. We performed in vivo experiments in pressurized aquaria to determine the upper thermal limit [critical thermal maximum (CT_max)] of R. exoculata and to investigate some characteristics of the shrimp stress response to heat exposure. These experiments showed that the shrimp does not tolerate sustained exposure to temperatures in the 33-37°C range (CT_max). A heat-inducible stress protein belonging to the hsp70 family was identified in R. exoculata, and its synthesis threshold induction temperature is below 25°C. The R. exoculata optimal thermal habitat may thus be restricted to values lower than previously expected (<25°C).