Abstract

1. The sea urchin Strongylocentrotus franciscanus acclimated at 15°C, 18°C and 21°C exposed to a rising thermal stress showed a series of well-defined responses. 2. All responses were significantly different and stage E4, characterized when the sea urchins ceased moving, relaxed the large spines but the smaller spines continued to make small movements. This was considered to be the critical thermal maximum (CTMax). 3. The resistance of S. franciscanus is independent of the acclimation interval used in this work. 4. The effect of the CTMax on the osmotic pressure of the sea urchin body fluid acclimated at 18°C was significantly different (P<0.05) when compare to the 15°C and 21°C conditions. © 2004 Elsevier Ltd. All rights reserved.