Correlated effects of ocean acidification and warming on behavioral and metabolic traits of a large pelagic fish

Ocean acidification and warming are co-occurring stressors, yet their effects on early life stages of large pelagic fishes are not well known. Here, we determined the effects of elevated CO2 and temperature at levels projected for the end of the century on activity levels, boldness, and metabolic traits (i.e., oxygen uptake rates) in larval kingfish (Seriola lalandi), a large pelagic fish with a circumglobal distribution. We also examined correlations between these behavioral and physiological traits measured under different treatments. Kingfish were reared from the egg stage to 25 days post-hatch in a full factorial design of ambient and elevated CO2 (~500 µatm and ~1000 µatm) and temperature (21 °C and 25 °C). Activity levels were higher in fish from the elevated temperature treatment compared with fish reared under ambient temperature. However, elevated CO2 did not affect activity, and boldness was not affected by either elevated CO2 or temperature. Both elevated CO2 and temperature resulted in increased resting oxygen uptake rates compared to fish reared under ambient conditions, but neither affected maximum oxygen uptake rates nor aerobic scope. Resting oxygen uptake rates and boldness were negatively correlated under ambient temperature, but positively correlated under elevated temperature. Maximum oxygen uptake rates and boldness were also negatively correlated under ambient temperature. These findings suggest that elevated temperature has a greater impact on behavioral and physiological traits of larval kingfish than elevated CO2. However, elevated CO2 exposure did increase resting oxygen uptake rates and interact with temperature in complex ways. Our results provide novel behavioral and physiological data on the responses of the larval stage of a large pelagic fish to ocean acidification and warming conditions, demonstrate correlations between these traits, and suggest that these correlations could influence the direction and pace of adaptation to global climate change

Testing the Adaptive Potential of Yellowtail Kingfish to Ocean Warming and Acidification

Estimating the heritability and genotype by environment (GxE) interactions of performance-related traits (e.g., growth, survival, reproduction) under future ocean conditions is necessary for inferring the adaptive potential of marine species to climate change. To date, no studies have used quantitative genetics techniques to test the adaptive potential of large pelagic fishes to the combined effects of elevated water temperature and ocean acidification. We used an experimental approach to test for heritability and GxE interactions in morphological traits of juvenile yellowtail kingfish, Seriola lalandi, under current-day and predicted future ocean conditions. We also tracked the fate of genetic diversity among treatments over the experimental period to test for selection favoring some genotypes over others under elevated temperature and CO2. Specifically, we reared kingfish to 21 days post hatching (dph) in a fully crossed 2 × 2 experimental design comprising current-day average summer temperature (21°C) and seawater pCO2 (500 μatm CO2) and elevated temperature (25°C) and seawater pCO2 (1,000 μatm CO2). We sampled larvae and juveniles at 1, 11, and 21 dph and identified family of origin of each fish (1,942 in total) by DNA parentage analysis. The animal model was used to estimate heritability of morphological traits and test for GxE interactions among the experimental treatments at 21 dph. Elevated temperature, but not elevated CO2 affected all morphological traits. Weight, length and other morphological traits in juvenile yellowtail kingfish exhibited low but significant heritability under current day and elevated temperature. However, there were no measurable GxE interactions in morphological traits between the two temperature treatments at 21 dph. Similarly, there was no detectable change in any of the measures of genetic diversity over the duration of the experiment. Nonetheless, one family exhibited differential survivorship between temperatures, declining in relative abundance between 1 and 21 dph at 21°C, but increasing in relative abundance between 1 and 21 dph at 25°C. This suggests that this family line could perform better under future warming than in current-day conditions. Our results provide the first preliminary evidence of the adaptive potential of a large pelagic fisheries species to future ocean conditions

Elevated CO₂ affects anxiety but not a range of other behaviours in juvenile yellowtail kingfish

Elevated seawater CO2 can cause a range of behavioural impairments in marine fishes. However, most studies to date have been conducted on small benthic species and very little is known about how higher oceanic CO2 levels could affect the behaviour of large pelagic species. Here, we tested the effects of elevated CO2, and where possible the interacting effects of high temperature, on a range of ecologically important behaviours (anxiety, routine activity, behavioural lateralization and visual acuity) in juvenile yellowtail kingfish, Seriola lalandi. Kingfish were reared from the egg stage to 25 days post-hatch in a full factorial design of ambient and elevated CO2 (similar to 500 and similar to 1000 mu atm pCO(2)) and temperature (21 degrees C and 25 degrees C). The effects of elevated CO2 were trait-specific with anxiety the only behaviour significantly affected. Juvenile S. lalandi reared at elevated CO2 spent more time in the dark zone during a standard black-white test, which is indicative of increased anxiety. Exposure to high temperature had no significant effect on any of the behaviours tested. Overall, our results suggest that juvenile S. lalandi are largely behaviourally tolerant to future ocean acidification and warming. Given the ecological and economic importance of large pelagic fish species more studies investigating the effect of future climate change are urgently needed