Effects of Ocean Acidification on the Larvae of a High-Value Pelagic Fisheries Species, Mahi-Mahi (Coryphaena hippurus)

Impacts of CO₂-induced ocean acidification have proven to be variable both among and within taxa. For fishes, inconsistent results and a limited number of study species confounds our ability to draw conclusions that apply across taxonomic groups. We present data from three experiments on larval mahi-mahi (Coryphaena hippurus), which were raised for up to 21 d under ambient seawater conditions (350 to 490 μatm pCO₂) and projected scenarios of ocean acidification (770 to 2170 μatm pCO₂). Evaluation of hatch rate, larval size, development, swimming activity, swimming ability (U_crit), and otolith (ear-stone) formation produced few significant effects. Larvae unexpectedly exhibited significantly larger size-at-age and faster developmental rate during one out of three experiments, possibly driven by metabolic compensation to elevated pCO₂ via a corresponding significant decrease in routine swimming velocity. Furthermore, larvae had significantly larger otoliths at 2170 μatm pCO₂, with potential implications for hearing sensitivity. The few observed effects on most variables measured in this study provide an optimistic indication that this species may not be overly susceptible to ocean acidification. However, the presence of some treatment effects suggests more subtle, but possibly widespread, effects of acidification on larval mahi-mahi, the cumulative consequences of which are currently unknown.