Abstract
When organisms are unable to feed ad libitum they may be more susceptible to negative effects of environmental stressors such as ocean acidification and warming (OAW). We reared sea bass (Dicentrarchus labrax) at 15 or 20 °C and at ambient or high PCO2 (650 versus 1750 µatm PCO2; pH = 8.1 or 7.6) at ad libitum feeding and observed no discernible effect of PCO2 on the size-at-age of juveniles after 277 (20 °C) and 367 (15 °C) days. Feeding trials were then conducted including a restricted ration (25% ad libitum). At 15 °C, growth rate increased with ration but was unaffected by PCO2. At 20 °C, acidification and warming acted antagonistically and low feeding level enhanced PCO2 effects. Differences in growth were not merely a consequence of lower food intake but also linked to changes in digestive efficiency. The specific activity of digestive enzymes (amylase, trypsin, phosphatase alkaline and aminopeptidase N) at 20 °C was lower at the higher PCO2 level. Our study highlights the importance of incorporating restricted feeding into experimental designs examining OAW and suggests that ad libitum feeding used in the majority of the studies to date may not have been suitable to detect impacts of ecological significance.
Highlights
When organisms are unable to feed ad libitum they may be more susceptible to negative effects of environmental stressors such as ocean acidification and warming (OAW)
15 months after European sea bass larvae were exposed to an 8-day hypoxic episode, their growth rates and protein digestive capacity were still lower than those from siblings maintained in normoxia[24]
We examined the growth rate and digestive capacity of juvenile sea bass (Dicentrarchus labrax) fed ad libitum or restricted (25% of ad libitum) rations at an ambient and an elevated (+1100 μatm) level of PCO2
Summary
When organisms are unable to feed ad libitum they may be more susceptible to negative effects of environmental stressors such as ocean acidification and warming (OAW). Ad libitum rations may provide ample energy allowing organisms to compensate for potential negative impacts of sub-optimal levels of temperature and/or PCO2 on energy acquisition, dissipation and allocation Invertebrates such as corals, mussels and oysters maintained on restricted rations displayed more deleterious effects to OAW than well-fed conspecifics[15,16,17,18]. Only very recent studies have examined the influence of the interaction between CO2 and food ration on larval growth and development[19,20,21,22] They showed either no supplementary effect with food restriction[19,20] or observed larger individuals but with important organ damages[22]. There is no evidence yet that digestive function might be affected, Strobel et al.[26] demonstrated that in an exposure of an Antarctic fish to 2000 μatm PCO2, regulation of acid-base balance occurred at the detriment of other processes such as calcification or osmoregulation likely due to changes in energy allocation
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