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.

Effects of high temperature and CO2 on intracellular DMSP in the cold-water coral Lophelia pertusa

Significant warming and acidification of the oceans is projected to occur by the end of the century. CO2 vents, areas of upwelling and downwelling, and potential leaks from carbon capture and storage facilities may also cause localised environmental changes, enhancing or depressing the effect of global climate change. Cold-water coral ecosystems are threatened by future changes in carbonate chemistry, yet our knowledge of the response of these corals to high temperature and high CO2 conditions is limited. Dimethylsulphoniopropionate (DMSP), and its breakdown product dimethylsulphide (DMS), are putative antioxidants that may be accumulated by invertebrates via their food or symbionts, although recent research suggests that some invertebrates may also be able to synthesise DMSP. This study provides the first information on the impact of high temperature (12 °C) and high CO2 (817 ppm) on intracellular DMSP in the cold-water coral Lophelia pertusa from the Mingulay Reef Complex, Scotland (56°49' N, 07°23' W), where in situ environmental conditions are meditated by tidally induced downwellings. An increase in intracellular DMSP under high CO2 conditions was observed, whilst water column particulate DMS + DMSP was reduced. In both high temperature treatments, intracellular DMSP was similar to the control treatment, whilst dissolved DMSP + DMS was not significantly different between any of the treatments. These results suggest that L. pertusa accumulates DMSP from the surrounding water column; uptake may be up-regulated under high CO2 conditions, but mediated by high temperature. These results provide new insight into the biotic control of deep-sea biogeochemistry and may impact our understanding of the global sulphur cycle, and the survival of cold-water corals under projected global change.

Nematode abundance of the Eastern Mediterranean Sea in cold seep sediments collected during Maria S. Merain cruises MSM13/3 and MSM13/4 in 2009

Sediment was collected by either push cores operated by the ROV Quest or by a television guided Multicorer. Nematodes abundance were calculated of the top 5 cm of the sediment to gain individual abundance per 10 cm**2.

Differential response of two Mediterranean cold-water coral species to ocean acidification

Cold-water coral (CWC) reefs constitute one of the most complex deep-sea habitats harboring a vast diversity of associated species. Like other tropical or temperate framework builders, these systems are facing an uncertain future due to several threats, such as global warming and ocean acidification. In the case of Mediterranean CWC communities, the effect may be exacerbated due to the greater capacity of these waters to absorb atmospheric CO2 compared to the global ocean. Calcification in these organisms is an energy-demanding process, and it is expected that energy requirements will be greater as seawater pH and the availability of carbonate ions decrease. Therefore, studies assessing the effect of a pH decrease in skeletal growth, and metabolic balance are critical to fully understand the potential responses of these organisms under a changing scenario. In this context, the present work aims to investigate the medium- to long-term effect of a low pH scenario on calcification and the biochemical composition of two CWCs from the Mediterranean, Dendrophyllia cornigera and Desmophyllum dianthus. After 314 d of exposure to acidified conditions, a significant decrease of 70 % was observed in Desmophyllum dianthus skeletal growth rate, while Dendrophyllia cornigera showed no differences between treatments. Instead, only subtle differences between treatments were observed in the organic matter amount, lipid content, skeletal microdensity, or porosity in both species, although due to the high variability of the results, these differences were not statistically significant. Our results also confirmed a heterogeneous effect of low pH on the skeletal growth rate of the organisms depending on their initial weight, suggesting that those specimens with high calcification rates may be the most susceptible to the negative effects of acidification.

Rapid acclimation of juvenile corals to CO2-mediated acidification by upregulation of heat shock protein and Bcl-2 genes

Corals play a key role in ocean ecosystems and carbonate balance, but their molecular response to ocean acidification remains unclear. The only previous whole-transcriptome study documented extensive disruption of gene expression, particularly of genes encoding skeletal organic matrix proteins, in juvenile corals (Acropora millepora) after short-term (3 d) exposure to elevated pCO2. In this study, whole-transcriptome analysis was used to compare the effects of such 'acute' (3 d) exposure to elevated pCO2 with a longer ('prolonged'; 9 d) period of exposure beginning immediately post-fertilization. Far fewer genes were differentially expressed under the 9-d treatment, and although the transcriptome data implied wholesale disruption of metabolism and calcification genes in the acute treatment experiment, expression of most genes was at control levels after prolonged treatment. There was little overlap between the genes responding to the acute and prolonged treatments, but heat shock proteins (HSPs) and heat shock factors (HSFs) were over-represented amongst the genes responding to both treatments. Amongst these was an HSP70 gene previously shown to be involved in acclimation to thermal stress in a field population of another acroporid coral. The most obvious feature of the molecular response in the 9-d treatment experiment was the upregulation of five distinct Bcl-2 family members, the majority predicted to be anti-apoptotic. This suggests that an important component of the longer term response to elevated CO2 is suppression of apoptosis. It therefore appears that juvenile A. millepora have the capacity to rapidly acclimate to elevated pCO2, a process mediated by upregulation of specific HSPs and a suite of Bcl-2 family members.