Growth of the estuarine fish <i>Fundulus heteroclitus</i> in response to diel-cycling hypoxia and acidification: interaction with temperature

Abstract

Growth rate of Fundulus heteroclitus was examined at 25 and 30 °C in nine treatments of diel-cycling dissolved oxygen (DO) and pH. Extreme diel-cycling DO (1–11 mg O 2 ·L −1 ) negatively impacted growth during 10 days at 30 °C, but not at 25 °C. Moderate DO cycles (3–9 mg O 2 ·L −1 ) had no direct growth impact at either temperature. Fish did not appear to acclimate, during days 10–30, to the initial growth-limiting effects of extreme diel DO cycles at 30 °C. Diel-cycling DO interacts synergistically with temperature to impact growth. There was no evidence of an independent growth effect of either moderate pH cycles (7.2–7.8) or extreme pH cycles (6.8–8.1) at either temperature. Mean low pCO 2 levels in extreme cycles were ∼32 000 and ∼47 000 μatm at 25 and 30 °C, respectively. It is noteworthy that these high mean nightly pCO 2 levels are more than an order of magnitude higher than the chronic mean oceanic pCO 2 of ∼1000 μatm projected by the year 2100.