Abstract
Extreme climatic events, such as heatwaves, are predicted to be more prevalent in future due to global climate change. The devastating impacts of heatwaves on the survival of marine organisms may be further intensified by ocean acidification. Here, we tested the hypothesis that prolonged exposure to heatwave temperatures (24 °C, +3 °C summer seawater temperature) would diminish energy budget, body condition and ultimately survival of a subtidal gastropod (Thalotia conica) by pushing close to its critical thermal maximum (CTmax). We also tested whether ocean acidification (pCO2: 1000 ppm) affects energy budget, CTmax and hence survival of this gastropod. Following the 8-week experimental period, mortality was markedly higher at 24 °C irrespective of pCO2 level, probably attributed to energy deficit (negative scope for growth) and concomitant depletion of energy reserves (reduced organ weight to flesh weight ratio). CTmax of T. conica appeared at 27 °C and was unaffected by ocean acidification. Our findings imply that prolonged exposure to heatwaves can compromise the survival of marine organisms below CTmax via disruption in energy homeostasis, which possibly explains their mass mortality in the past heatwave events. Therefore, heatwaves would have more profound effects than ocean acidification on future marine ecosystems.
Highlights
Since the onset of Industrial Revolution, atmospheric carbon dioxide concentration has been increasing rapidly and caused observable changes in marine ecosystems
Provided prolonged exposure to heatwaves diminishes the survival of this subtidal gastropod through energy depletion even below its thermal tolerance, this mechanism helps explain the mass mortality of marine organisms in the past heatwave events, and suggests that persistent heatwaves are the main driver of the functions of both contemporary and future marine ecosystems
Contrary to theory[22], we revealed that ocean acidification (OA) did not significantly affect the thermal tolerance, energy budget, body condition and survival of a subtidal gastropod, even though the individuals had limited time to acclimate
Summary
Since the onset of Industrial Revolution, atmospheric carbon dioxide (pCO2) concentration has been increasing rapidly and caused observable changes in marine ecosystems. One of the most devastating extreme climatic events, are of special concern because they can abruptly increase the sea surface temperature along coastlines by ~3 °C on average and persist for more than two months, causing substantial changes in marine ecosystems[10,11,12]. We examined the effects of prolonged exposure to elevated pCO2 and temperature on the energy budget, body condition and survival of a subtidal grazing gastropod Thalotia conica, which is widely distributed in temperate Australia. Provided prolonged exposure to heatwaves diminishes the survival of this subtidal gastropod through energy depletion even below its thermal tolerance, this mechanism helps explain the mass mortality of marine organisms in the past heatwave events, and suggests that persistent heatwaves are the main driver of the functions of both contemporary and future marine ecosystems
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