The Effects of Oxygen Supply when Immersed on the Thermal Limits and Performance of the Wave Zone Echinoderm Colobocentrotus atratus

Abstract

Thermal limits of marine ectotherms are hypothesized to be limited by oxygen demand. This limit arises from an animal’s metabolic demand outpacing oxygen supply and delivery with increasing temperatures. We applied this theory to the intertidal zone, where animals are exposed to extreme temperature ranges and emersion, to examine how oxygen delivery capacity can limit vertical distributions of organisms. We tested the upper thermal limit of performance (survival and attachment strength) in a wave-zone obligate urchin, Colobocentrotus atratus, under both ambient (21%) and enriched (35%) O2 conditions, to determine if these urchins are limited by oxygen availability in water when exposed to temperatures ranging from 25 to 37⁰C. Survival when thermally stressed was increased by enriched O2 conditions, indicating oxygen limitation of C. atratus under submerged conditions. Attachment strength declined with increasing temperature, but was not affected by O2 enrichment. Our data support that the lower limit on vertical distributions of C. atratus are set by abiotic conditions resulting from oxygen limitation when submerged.