Abstract
Ocean warming and acidification act concurrently on marine ectotherms with the potential for detrimental, synergistic effects; yet, effects of these stressors remain understudied in large predatory fishes, including sharks. We tested for behavioural and physiological responses of blacktip reef shark (Carcharhinus melanopterus) neonates to climate change relevant changes in temperature (28 and 31 °C) and carbon dioxide partial pressures (pCO2; 650 and 1050 µatm) using a fully factorial design. Behavioural assays (lateralisation, activity level) were conducted upon 7–13 days of acclimation, and physiological assays (hypoxia tolerance, oxygen uptake rates, acid–base and haematological status) were conducted upon 14–17 days of acclimation. Haematocrit was higher in sharks acclimated to 31 °C than to 28 °C. Significant treatment effects were also detected for blood lactate and minimum oxygen uptake rate; although, these observations were not supported by adequate statistical power. Inter-individual variability was considerable for all measured traits, except for haematocrit. Moving forward, studies on similarly ‘hard-to-study’ species may account for large inter-individual variability by increasing replication, testing larger, yet ecologically relevant, differences in temperature and pCO2, and reducing measurement error. Robust experimental studies on elasmobranchs are critical to meaningfully assess the threat of global change stressors in these data-deficient species.
Highlights
Ocean warming and acidification act concurrently on marine ectotherms with the potential for detrimental, synergistic effects; yet, effects of these stressors remain understudied in large predatory fishes, including sharks
We were unable to detect treatment effects on the relative lateralisation index (LR; turning preference scored from − 100 to 100, where positive LR indicates a right turning bias; Fig. 1A)
Blacktip reef shark neonates exhibited an increase in Hct upon exposure to 31 °C when compared to sharks maintained at 28 °C
Summary
Ocean warming and acidification act concurrently on marine ectotherms with the potential for detrimental, synergistic effects; yet, effects of these stressors remain understudied in large predatory fishes, including sharks. Unabated climate change projections for the year 2100 suggest that sea surface temperatures will increase by 3–5 °C (ocean warming), and carbon dioxide partial pressures (pCO2) will increase by ~ 600 μatm (ocean acidification; OA) in pelagic environments; projections are more extreme and variable in coastal environments[2]. These global change phenomena are predicted to affect the fitness and survival of marine ectotherms through reductions in an organism’s physiological oxygen supply c apacity[3]. Despite the complexity of responses observed to date for an impressive diversity of marine taxa, ecological roles, and habitat types, pervasive knowledge gaps remain
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