Abstract
Eutrophication-induced hypoxia is one of the primary anthropogenic threats to coastal ecosystems. Under hypoxic conditions, a deficit of O-2 and a surplus of CO2 will concurrently decrease pH, yet studies of hypoxia have seldom considered the potential interactions with elevated pCO(2) (reduced pH). Previous studies on gelatinous organisms concluded that they are fairly robust to low oxygen and reduced pH conditions individually, yet the combination of stressors has only been examined for ephyrae. The goals of this study were to determine the individual and interactive effects of hypoxia and elevated pCO(2) on the asexual reproduction and aerobic respiration rates of polyps of the scyphozoan Aurelia aurita during a manipulative experiment that ran for 36 d. pCO(2) and pO(2) were varied on a diel basis to closely mimic the diel conditions ob served in the field. Exposure to low dissolved oxygen (DO) reduced asexual budding of polyps by similar to 50% relative to control conditions. Under hypoxic conditions, rates of respiration were elevated during an initial acclimation period (until Day 8), but respiration rates did not differ between DO levels under prolonged exposure. There was no significant effect of increased pCO(2) on either asexual reproduction or aerobic respiration, suggesting that elevated pCO(2) (reduced pH) did not exacerbate the negative reproductive effects of hypoxia on A. aurita polyps.