Effects of ocean acidification on the larvae of a high-value pelagic fisheries species, mahi-mahi Coryphaena hippurus

S Bignami,Rk Cowen,S Sponaugle

doi:10.3354/ab00598

Abstract

Negative impacts of CO2-induced ocean acidification on marine organisms have proven to be variable both among and within taxa. For fishes, inconsistency confounds our ability to draw conclusions that apply across taxonomic groups and highlights the limitations of a nascent field with a narrow scope of study species. Here, we present data from a series of 3 experiments on the larvae of mahi-mahi Coryphaena hippurus, a large pelagic tropical fish species of high eco- nomic value. Mahi-mahi larvae were raised for up to 21 d under either ambient seawater condi- tions (350 to 490 µatm pCO2) or projected scenarios of ocean acidification (770 to 2170 µatm pCO2). Evaluation of hatch rate, larval size, development, swimming activity, swimming ability (Ucrit), and otolith (ear stone) formation produced few significant effects. However, larvae unex- pectedly exhibited significantly larger size-at-age and faster developmental rate during 1 out of 3 experiments, possibly driven by metabolic compensation to elevated pCO2 via a corresponding decrease in routine swimming velocity. Furthermore, larvae had significantly larger otoliths at 2170 µatm pCO2, and a similar but non-significant trend also occurred at 1200 µatm pCO2, sug- gesting potential implications for hearing sensitivity. The lack of effect on most variables meas- ured in this study provides an optimistic indication that this large tropical species, which inhabits the offshore pelagic environment, may not be overly susceptible to ocean acidification. However, the presence of some treatment effects on growth, swimming activity, and otolith formation sug- gests the presence of subtle, but possibly widespread, effects of acidification on larval mahi-mahi, the cumulative consequences of which are still unknown.

Highlights

A diversity of marine organisms are negatively affected by CO2-induced ocean acidification, yet the occurrence and severity of such effects are highly variable among taxa and life history stages (Kroeker et al 2013)
We present data from a series of experiments that investigated a suite of factors that are comparable to those reported for larval cobia and other species, including hatch rate, growth, development, swimming activity, critical swimming speed (Ucrit), and otolith formation (Munday et al 2009, Baumann et al 2011, Bignami et al 2013a)
No metric of routine swimming activity was affected by CO2 treatment, and larvae did not exhibit any treatment-related change in swimming activity following olfactory stimulation with food-scented water

Summary

Introduction

A diversity of marine organisms are negatively affected by CO2-induced ocean acidification, yet the occurrence and severity of such effects are highly variable among taxa and life history stages (Kroeker et al 2013). Several other studies report no pCO2 effects on fish larvae (e.g. Munday et al 2011b, Frommel et al 2013). Though intriguing, this interand intra-specific variability in response to ocean acidification confounds our ability to formulate general conclusions regarding the fate of fish populations under future environmental scenarios. Most studies of ocean acidification impacts on fish larvae have focused on demersal, reef-associated species, with few large pelagic species represented in the literature (except see Checkley et al 2009, Bignami et al 2013a,b, Pimentel et al 2014b)

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Conclusion