Preferred Temperature, Critical Thermal Maximum, and Metabolic Response of the Black Sea Urchin<i>Arbacia stellata</i>(Blainville, 1825; Gmelin, 1791)

Abstract

Populations of the black sea urchin Arbacia stellata present in the Gulf of California and outer Pacific Coast area are probably the result of colonization from the Panamic region. In the Pacific Coast of Baja California, this species experiences seasonal fluctuations of temperature. It was determined the preferred temperature (PT), critical threshold limits represented for Critical Thermal Maximum (CTMax) and oxygen consumption rate in organisms acclimated to 16°C, 19°C, 22°C, and 25°C in controlled conditions. The PT of A. stellata was determined in organisms using the acute method. As the acclimation temperature increases, the PT also increases significantly (P < 0.05) and decreases to 22.8°C. In the acclimation temperature of 25°C, PT for black sea urchins was 23.3°C ± 0.3°C. A direct relation was determined between the CTMax and acclimation temperatures being of 36.48°C ± 0.6°C, 37.64°C ± 0.76°C, 38.08°C ± 0.94°C, 38.42°C ± 0.71°C. The end point of CTMax was stage E4, where the sea urchins stop moving, relax the large spines but activity continues with light movements of small spines and when the organisms lose the ability to remain attached to the substrate. The oxygen consumption rates increased significantly (P < 0.05) from 5.59 to 11.5 mg O2 kg/h wet weight (w.w.) as the acclimation temperature increased from 16°C to 25°C. The range of temperature coefficient (Q10) between 16°C and 25°C (lowest) was 1.90, indicating that within that range of acclimation temperature, organisms are adapted to maintain homeostasis. This corresponded with the interval of PT of the species. These results may partially explain their distribution pattern in Baja California Coast.