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. purpu- ratus was determined in a horizontal thermal gradient. The preferred temperature select by the red sea urchin was 17.5 ± 0.3 oC during the diurnal cycle and 16.8 ± 0.4 oC for the night. The purple sea urchin preferred temperature during day- time of 18.8 ± 0.2 oC and night was 17.4 ± 0.3 oC. For both species of sea urchin preferendum between day and night cy- cles were different (P < 0.05), the purple sea urchin preferred higher temperatures that red read 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.