Oxygen-limited performance of the intertidal sea urchin Colobocentrotus atratus when submerged

Thermal limits of marine ectotherms are influenced by the dynamics of oxygen supply and demand; all else being equal, as temperature increases, metabolic demand eventually outpaces an organism's capacity for oxygen uptake and delivery. We tested the combined effects of oxygen and temperature on an intertidal wave-zone obligate sea urchin, Colobocentrotus atratus, to examine whether oxygen limitation during submersion may limit the lower vertical distribution of this species. We measured survival and attachment strength under both ambient (21%) and enriched (35%) O2 conditions and at a range of temperatures between 25 and 37 °C. Oxygen enrichment increased survival at warmer temperatures, demonstrating oxygen limitation during submergence at high temperatures. Attachment strength declined with increasing temperature, but, unlike survivorship, was not affected by O2 enrichment. Our data suggest that the lower limit on vertical distributions of C. atratus are set in part by abiotic stresses experienced under immersion, and that hypoxic stress will increase with warming sea temperatures. Thus, warmer oceans may reduce the amount of viable habitat for C. atratus, and other intertidal marine taxa that are specialized for aerial gas exchange, due to increasing abiotic stress at the bottom of their vertical distribution.