Metabolic responses of the Nereid polychaete, Alitta succinea, to hypoxia at varying temperature.

Metabolism, like virtually all characteristics of organisms, varies predictably with body size, temperature, and chemical composition. In coastal systems that develop hypoxia, the metabolic rates of organisms are adversely affected often leading to mortality. Of particular concern is the physiological effect of hypoxia on macrobenthos, sessile organisms that have a key influence on benthic processes via bioturbation. Using a novel stopflow respirometry system, the metabolic responses of the Nereid polychaetes Alitta succinea were assessed during hypoxia at two temperature treatments to better understand the relationship between hypoxia and temperature on metabolism. Specifically, during hypoxia we quantified: the resting metabolic rate (V_O2); critical oxygen saturation (i.e. the oxygen level below which polychaetes could not maintain aerobic metabolism); and the oxyregulation ability at an acclimation temperature (25^o C) and after an acute temperature increase (to 30^o C). As represented by Q₁₀ (a temperature coefficient that measures the fractional change as a consequence of increasing temperature), we found hypoxia to completely mute the effect of temperature on metabolism, indicating hypoxia had a stronger influence on metabolism than temperature. Unlike most polychaetes, A. succinea was found to posses the ability to maintain aerobic metabolism despite changing O₂ (i.e. oxyregulation), and had the lowest critical oxygen saturations levels found in the literature of 16% and 10% at 25 and 30 ^oC, respectively. These findings demonstrate the significant effect of hypoxia on A. succinea metabolism, but also provide a metabolic justification for survival of this polychaete during hypoxia.