Hypoxia tolerance in coral-reef triggerfishes (Balistidae)
Despite high rates of photosynthetic oxygen production during the day, the warm waters of coral reefs are susceptible to hypoxia at night due to elevated respiration rates at higher temperatures that also reduce the solubility of oxygen. Hypoxia may be a challenge for coral-reef fish that hide in the reef to avoid predators at night. Triggerfishes (Balistidae) are found in a variety of reef habitats, but they also are known to find refuge in reef crevices and holes at night, which may expose them to hypoxic conditions. The critical oxygen tension (P crit) was determined as the point below which oxygen uptake could not be maintained to support standard metabolic rate (SMR) for five species of triggerfish. The triggerfishes exhibited similar levels of hypoxia tolerance as other coral-reef and coastal marine fishes that encounter low oxygen levels in their environment. Two species, Rhinecanthus rectangulus and R. aculeatus, had the lowest P crit (~ 3.0 kPa O2), comparable to the most hypoxia-tolerant obligate coral-dwelling gobies, while Odonus niger and Sufflamen bursa were moderately tolerant to hypoxia (P crit ~ 4.5 kPa), and Xanthichthys auromarginatus was intermediate (P crit ~ 3.7 kPa). These differences in P crit were not due to differences in oxygen demand, as all the species had a similar SMR once mass differences were taken into account. The results suggest that triggerfish species are adapted for different levels of hypoxia exposure during nocturnal sheltering within the reef.
KeywordsCritical oxygen tension Respirometry Standard metabolic rate Dissolved oxygen Scaling Oxygen consumption
The authors thank Captain Brian Quinn for assistance with oxygen data logger deployment and Kat Mowle, Travis Marcoux, and Stacia Goecke for assistance with data collection. We also thank Dr. K. David Hyrenbach for advice on the use of statistics.
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