Effects of elevated CO2 on fish behaviour undiminished by transgenerational acclimation

Behaviour and sensory performance of marine fishes are impaired at CO2 levels projected to occur in the ocean in the next 50-100 years, and there is limited potential for within-generation acclimation to elevated CO2. However, whether fish behaviour can acclimate or adapt to elevated CO2 over multiple generations remains unanswered. We tested for transgenerational acclimation of reef fish olfactory preferences and behavioural lateralization at moderate (656 µatm) and high (912 µatm) end-of-century CO2 projections. Juvenile spiny damselfish, Acanthochromis polyacanthus, from control parents (446 µatm) exhibited an innate avoidance to chemical alarm cue (CAC) when reared in control conditions. In contrast, juveniles lost their innate avoidance of CAC and even became strongly attracted to CAC when reared at elevated CO2 levels. Juveniles from parents maintained at mid-CO2 and high-CO2 levels also lost their innate avoidance of CAC when reared in elevated CO2, demonstrating no capacity for transgenerational acclimation of olfactory responses. Behavioural lateralization was also disrupted for juveniles reared under elevated CO2, regardless of parental conditioning. Our results show minimal potential for transgenerational acclimation in this fish, suggesting that genetic adaptation will be necessary to overcome the effects of ocean acidification on behaviour.

Annual response of two Mediterranean azooxanthellate temperate corals to low-pH and high-temperature conditions

Ocean acidification (OA) and warming related to the anthropogenic increase in atmospheric CO2 have been shown to have detrimental effects on several marine organisms, especially those with calcium carbonate structures such as corals. In this study, we evaluate the response of two Mediterranean shallow-water azooxanthellate corals to the projected pH and seawater temperature (ST) scenarios for the end of this century. The colonial coral Astroides calycularis and the solitary Leptopsammia pruvoti were grown in aquaria over a year under two fixed pH conditions, control (8.05 pHT units) and low (7.72 pHT units), and simulating two annual ST cycles, natural and high (+3 °C). The organic matter (OM), lipid and protein content of the tissue and the skeletal microdensity of A. calycularis were not affected by the stress conditions (low pH, high ST), but the species exhibited a mean 25 % decrease in calcification rate at high-ST conditions at the end of the warm period and a mean 10 % increase in skeletal porosity under the acidified treatment after a full year cycle. Conversely, an absence of effects on calcification and skeletal microdensity of L. pruvoti exposed to low-pH and high-ST treatments contrasted with a significant decrease in the OM, lipid and protein content of the tissue at high-ST conditions and a 13 % mean increase in the skeletal porosity under low-pH conditions following a full year of exposure. This species-specific response suggests that different internal self-regulation strategies for energy reallocation may allow certain shallow-water azooxanthellate corals to cope more successfully than others with global environmental changes.

Methylation index of Branched Tetraethers (MBT) and Cyclization ratio of Branched Tetraethers (CBT), annual mean air temperature and soil pH of sediment core GeoB6518-1 in the Congo River basin

We analyzed the distribution of branched tetraether membrane lipids derived from soil bacteria in a marine sediment record that was recovered close to the Congo River outflow, and the results enabled us to reconstruct large-scale continental temperature changes in tropical Africa that span the past 25,000 years. Tropical African temperatures gradually increased from ~21° to 25°C over the last deglaciation, which is a larger warming than estimated for the tropical Atlantic Ocean. A direct comparison with sea-surface temperature estimates from the same core revealed that the land-sea temperature difference was, through the thermal pressure gradient, an important control on central African precipitation patterns.