Temperature-dependent hypoxia tolerance of purple sea urchin Strongylocentrotus purpuratus across biogeography and ontogeny

Abstract

ABSTRACT: Ocean warming is increasing organismal oxygen demand, yet at the same time the ocean’s oxygen supply is decreasing. For a patch of habitat to remain viable, there must be a minimum level of environmental oxygen available for an organism to fuel its metabolic demand—quantified as its critical oxygen partial pressure ( pO_2crit). The temperature-dependence of pO_2crit sets an absolute lower boundary on aerobically viable ocean space for a species, yet whether certain life stages or geographically distant populations differ in their temperature-dependent hypoxia tolerance remains largely unknown. To address these questions, we used the purple sea urchin Strongylocentrotus purpuratus as a model species and measured pO_2crit for 3 populations of adult urchins (Clallam Bay, WA [n = 39], Monterey Bay, CA [91], San Diego, CA [34]) spanning 5-22°C and for key embryonic and larval developmental phases (blastula [n = 11], gastrula [21], prism [31], early-pluteus [21], late-pluteus [14], settled [12]) at temperatures of 10-19°C. We found that temperature-dependent hypoxia tolerance is consistent among adult populations exposed to different temperature and oxygen regimes, despite variable basal oxygen demands, suggesting differential capacity to provision oxygen. Moreover, we did not detect evidence for a hypoxia tolerance bottleneck for any developmental phase. Earlier larval phases are associated with higher hypoxia tolerance and greater temperature sensitivity, while this pattern shifts towards lower hypoxia tolerance and reduced temperature sensitivity as larvae develop. Our results indicate that, at least for S. purpuratus, models quantifying aerobically viable habitat based on pO_2crit-temperature relationships from a single adult population will conservatively estimate viable habitat.