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

Abstract

Negative impacts of CO 2 -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 economic value. Mahi-mahi larvae were raised for up to 21 d under either ambient seawater conditions (350 to 490 µatm pCO 2 ) or projected scenarios of ocean acidification (770 to 2170 µatm pCO 2 ). Evaluation of hatch rate, larval size, development, swimming activity, swimming ability (U crit ), and otolith (ear stone) formation produced few significant effects. However, larvae unexpectedly exhibited significantly larger size-at-age and faster developmental rate during 1 out of 3 experiments, possibly driven by metabolic compensation to elevated pCO 2 via a corresponding decrease in routine swimming velocity. Furthermore, larvae had significantly larger otoliths at 2170 µatm pCO 2 , and a similar but non-significant trend also occurred at 1200 µatm pCO 2 , suggesting potential implications for hearing sensitivity. The lack of effect on most variables measured 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 suggests the presence of subtle, but possibly widespread, effects of acidification on larval mahi-mahi, the cumulative consequences of which are still unknown.KEY WORDS: Ocean acidification · Larval fish · Otolith · Mahi-mahi · CO 2 · U crit · Behavior OPEN PEN ACCESS CCESSAquat Biol 21: 249-260, 2014 250 cope with increased environmental partial pressure of carbon dioxide ( pCO 2 ). Embryonic and larval fishes are not equip ped with the same physiological mechanisms as juveniles and adults, but are capable of some internal pH regulation (Brauner 2008). Nonetheless, existing literature indicates that early life stages of fishes are more susceptible to elevated pCO 2 relative to adults (reviewed by Pörtner et al. 2005). As the primary period of dispersal for many marine fishes, the larval stage is critical to population replenishment and connectivity (Cowen & Sponaugle 2009); therefore, our understanding of the broader population-and ecosystem-level impacts of ocean acidification requires consid eration of this life stage.The impact of ocean acidification on larval fishes is highly variable among studies and taxa. The range of effects include reduced growth and survival (Baumann et al. 2011), skeletal deformation (Pimentel et al. 2014a), altered neurological function (Nilsson et al. 2012), and disrupted behavior (Munday et al. 2010, Ferrari et al. 2012, Hamilton et al. 2014. Some species have experienced m...

European sea bass show behavioural resilience to near-future ocean acidification

“…Fish showed statistically similar movements, interaction with their environment, and interaction with each other, regardless of whether they were raised and tested in ambient conditions, OA conditions, or raised under ambient conditions and tested in OA water. Overall, this indicates behavioural resilience to OA, supporting work on individual subjects showing that increased p CO 2 similarly has no significant effect on larval morphology in this species [24], and work on individual subjects (rather than groups) investigating swimming activity and/or kinematics in juvenile or larval fish; for example, studies of cobia ( Rachycentron canadum ) [29], mahi-mahi ( Coryphaena hippurus ) [30], Atlantic cod ( Gadus morhua ) [31] and herring ( Clupea harengus L.) [32] do not find an effect of elevated CO 2 . For an obligate schooling migratory fish like sea bass, our finding is good news, and suggests that we can be optimistic about their ability to cope with anthropogenic changes to their environment in the near future.…”

Ocean acidification boosts larval fish development but reduces the window of opportunity for successful settlement

“…Some studies have found reduced growth [53], while others find increased growth [17,54] and others no effect [18]. Similarly, swimming performances have been found to be unaffected by ocean acidification in some studies [17,18] or decreased in others [20]. Here, contrary to expectations [1], increased length in high CO 2 -reared fish was accompanied by a decrease in swimming velocity.…”

“…The effect of elevated CO 2 on fish swimming behaviour is also unresolved. Some studies suggest that swimming performances of larval fishes could be unaffected by ocean acidification [17,18], whereas others find ocean acidification alters activity levels [19,20] and one study suggests that ocean acidification can have an indirect effect on maximum swimming speed of settlement-stage larvae through increasing body size [21]. However, most of these studies have used different swimming behaviour metrics, making comparisons difficult to interpret.…”

Elevated carbon dioxide has limited acute effects on Lepomis macrochirus behaviour

“…Similarly, juvenile Atlantic cod Gadus morhua L. 1758 displayed no change in L R , L A or emergence from a shelter (an indicator of boldness) despite exposure to 995 μatm p CO 2 for 28 days (Jutfelt & Hedgärde, ). In addition, swimming speed of larval cobia Rachycentron canadum (L. 1766) was unaltered after exposure to 2100 μatm for 3 weeks (Bignami, ). Though untested in this study, the mechanisms that control boldness, lateralization and swimming performance may be less controlled by CO 2 in L. macrochirus when…”