Thermoregulatory Behavior of Red Sea Urchin Strongylocentrotus Fran-ciscanus (Agassiz, 1863) and Purple Sea Urchin Strongylocentrotus Purpu-ratus (Stimpson, 1857) (Echinodermata: Echinoidea)

Thermoregulatory behavior of red sea urchin Strongylocentrotus franciscanus and purple sea urchin S. purpuratus was determined in a horizontal thermal gradient. The preferred temperature select by the red sea urchin was 17.5 0.3 C during the diurnal cycle and 16.8 0.4 C for the night. The purple sea urchin preferred temperature during daytime of 18.8 0.2 C and night was 17.4 0.3 C. For both species of sea urchin preferendum between day and night cycles were different (P < 0.05), the purple sea urchin preferred higher temperatures that red urchin, suggesting that S. purpuratus use thermoregulatory behavior as a mechanism of environmental segregation to avoid competition for space and food with red sea urchin.