Oxygen consumption during and post-hypoxia exposure in bearded fireworms (Annelida: Amphinomidae)

Oxygen is necessary for all marine animals to support metabolic functions. When chronic low dissolved oxygen (DO) conditions occur, organisms must adjust to overcome this stressor's effect on metabolic rates. The bearded fireworm, Hermodice carunculata, is a widespread species frequently exposed to hypoxic conditions in areas within its broad distribution which may impact metabolism, wound healing, and regeneration. To study the impact of hypoxia on their metabolic rates, we exposed fireworms to two levels of lower than normal DO conditions (low 2.5 ± 0.25 mg O₂ L^-1 and mid 4.5 ± 0.25 mg O₂ L^-1) for 7 days by pumping nitrogen into their holding tanks. During a chronic hypoxia trial, we quantified oxygen consumption in each experimental group and subsequently determined post-hypoxia oxygen consumption of individuals from the lowest oxygen level. During the hypoxic exposure, the oxygen uptake rates declined in low and mid DO conditions, while remaining relatively constant for the normoxic (7.0 ± 0.25 mg O₂ L^-1) control. We then compared the oxygen consumption rates from the lowest DO condition to fireworms likely never exposed to hypoxia and fireworms from a location likely to be exposed to hypoxia. We found higher oxygen consumption rates in the experimentally hypoxia-exposed worms. These results suggest prolonged negative impacts of hypoxic exposure, leading to a lasting elevation of metabolic rates of these marine invertebrates. The increase in metabolic rates may lead to increased predation on their prey of choice, economically and commercially important coral, causing increased degradation of already threatened coral reef ecosystems.