MEPS prepress abstract   -  DOI: https://doi.org/10.3354/meps14817

ABSTRACT: Environments with fluctuating oxygen are intense challenges for organisms both on land and in the water. Aquatic organisms can be exposed to especially stressful bouts of hypoxia that come on rapidly and to extreme levels. The copepod Tigriopus californicus inhabits supralittoral rocky pools and appears tolerant of hypoxia considered lethal for other aquatic organisms despite lacking molecular components typically used by animals to detect and respond to low environmental oxygen. Here, we quantified the natural regime of dissolved oxygen (DO) pools inhabited by T. californicus via deployment of continuous oxygen sensors to copepod pools in Oregon, USA. Using wild-derived cultures from northern (Oregon) and southern (Californian) populations, we exposed copepods to hypoxia and anoxia and assayed loss of equilibrium (LOE) and survival. We also quantified respiratory regulation via the statistics P_crit, oxygen supply capacity (alpha), and RI (regulation index). We observed that pools underwent extreme daily cycles of DO and that near anoxia often persisted for up to 6 hours. Respiratory statistics indicated individuals could regulate oxygen consumption even near anoxia, predicting a species with hypoxia tolerance ranking high among aquatic taxa. Copepods survived hypoxia below 0.3 mg O₂ l^-1 for up to 72 hours with some individuals not showing any loss of equilibrium. Survival was high following even 6- and 15-hour exposure to anoxia. We observed sex and population differences in lethality and LOE, with southern populations exhibiting higher resilience. Intraspecific variation in tolerance makes this system a candidate for future studies to investigate alternative molecular and physiological pathways of hypoxia response.