Description: We tested the effect of near-future CO2 levels (= 490, 570, 700, and 960 µatm CO2) on the olfactory responses and activity levels of juvenile coral trout, Plectropomus leopardus, a piscivorous reef fish that is also one of the most important fisheries species on the Great Barrier Reef, Australia. Juvenile coral trout reared for 4 weeks at 570 µatm CO2 exhibited similar sensory responses and behaviors to juveniles reared at 490 µatm CO2 (control). In contrast, juveniles reared at 700 and 960 µatm CO2 exhibited dramatically altered sensory function and behaviors. At these higher CO2 concentrations, juveniles became attracted to the odor of potential predators, as has been observed in other reef fishes. They were more active, spent less time in shelter, ventured further from shelter, and were bolder than fish reared at 490 or 570 µatm CO2. These results demonstrate that behavioral impairment of coral trout is unlikely if pCO2 remains below 600 µatm; however, at higher levels, there are significant impacts on juvenile performance that are likely to affect survival and energy budgets, with consequences for predator-prey interactions and commercial fisheries.

Description: Carbon dioxide concentrations in the surface ocean are increasing owing to rising CO2 concentrations in the atmosphere. Higher CO2 levels are predicted to affect essential physiological processes of many aquatic organisms, leading to widespread impacts on marine diversity and ecosystem function, especially when combined with the effects of global warming. Yet the ability for marine species to adjust to increasing CO2 levels over many generations is an unresolved issue. Here we show that ocean conditions projected for the end of the century (approximately 1,000 µatm CO2 and a temperature rise of 1.5-3.0 °C) cause an increase in metabolic rate and decreases in length, weight, condition and survival of juvenile fish. However, these effects are absent or reversed when parents also experience high CO2 concentrations. Our results show that non-genetic parental effects can dramatically alter the response of marine organisms to increasing CO2 and demonstrate that some species have more capacity to acclimate to ocean acidification than previously thought.

Description: The appropriate behavioural response to predation risk is critical to survival; however, behavioural responses can be subjected to trade-offs. For example, individuals may engage in riskier foraging behaviour to secure sufficient energy if resources are limited. Additionally, elevated CO2 can influence foraging and antipredator behaviour of marine organisms. Yet, how the availability of energetic resources may influence antipredator behaviour in an elevated CO2environment is unknown. We tested the effects of food ration (low and high: 4 and 8% of body weight per day, respectively) on antipredator behaviour at ambient (489 µatm) and elevated (1022 µatm) CO2 in juvenile Amphiprion percula at 50 d post-hatching. Juveniles were from parents held at either ambient or elevated CO2, as parental exposure can influence phenotypic response in offspring. Antipredator behaviour was severely impaired by elevated CO2, with juveniles reared at elevated CO2 exhibiting no change in feeding rate in the presence of the predator cue compared with a 〉67% reduction in feeding rate in ambient CO2 fish. By contrast, food ration had a minor effect on the change in feeding rate in response to the predator cue, with only a 2.3% difference between high and low food ration fish. The effect of elevated CO2 on antipredator behaviour of juveniles was not influenced by food ration. Parental exposure to elevated CO2 influenced the baseline feeding rate and exhibited a small carry-over effect in elevated CO2 juveniles. These results suggest that reef fish could exhibit riskier behaviour at elevated CO2 levels, regardless of the energetic resources available.

Description: The persistence of most coastal marine species depends on larvae finding suitable adult habitat at the end of an offshore dispersive stage that can last weeks or months. We tested the effects that ocean acidification from elevated levels of atmospheric carbon dioxide (CO2) could have on the ability of larvae to detect olfactory cues from adult habitats. Larval clownfish reared in control seawater (pH 8.15) discriminated between a range of cues that could help them locate reef habitat and suitable settlement sites. This discriminatory ability was disrupted when larvae were reared in conditions simulating CO2-induced ocean acidification. Larvae became strongly attracted to olfactory stimuli they normally avoided when reared at levels of ocean pH that could occur ca. 2100 (pH 7.8) and they no longer responded to any olfactory cues when reared at pH levels (pH 7.6) that might be attained later next century on a business-as-usual carbon-dioxide emissions trajectory. If acidification continues unabated, the impairment of sensory ability will reduce population sustainability of many marine species, with potentially profound consequences for marine diversity.

Description: Determining which marine species are sensitive to elevated CO2 and reduced pH, and which species tolerate these changes, is critical for predicting the impacts of ocean acidification on marine biodiversity and ecosystem function. Although adult fish are thought to be relatively tolerant to higher levels of environmental CO2, very little is known about the sensitivity of juvenile stages, which are usually much more vulnerable to environmental change. We tested the effects of elevated environmental CO2 on the growth, survival, skeletal development and otolith (ear bone) calcification of a common coral reef fish, the spiny damselfish Acanthochromis polyacanthus. Newly hatched juveniles were reared for 3 wk at 4 different levels of PCO2(seawater) spanning concentrations already experienced in near-reef waters (450 µatm CO2) to those predicted to occur over the next 50 to 100 yr in the IPCC A2 emission scenario (600, 725, 850 µatm CO2). Elevated PCO2 had no effect on juvenile growth or survival. Similarly, there was no consistent variation in the size of 29 different skeletal elements that could be attributed to CO2 treatments. Finally, otolith size, shape and symmetry (between left and right side of the body) were not affected by exposure to elevated PCO2, despite the fact that otoliths are composed of aragonite. This is the first comprehensive assessment of the likely effects of ocean acidification on the early life history development of a marine fish. Our results suggest that juvenile A. polyacanthus are tolerant of moderate increases in environmental CO2 and that further acidification of the ocean will not, in isolation, have a significant effect on the early life history development of this species, and perhaps other tropical reef fishes

Description: Phenotypic plasticity, both within and across generations, is an important mechanism that organisms use to cope with rapid climate change. While an increasing number of studies show that plasticity across generations (transgenerational plasticity or TGP) may occur, we have limited understanding of key aspects of TGP, such as the environmental conditions that may promote it, its relationship to within generation plasticity (WGP) and its role in evolutionary potential. In this review, we consider how the detection of TGP in climate change experiments is affected by the predictability of environmental variation, as well as the timing and magnitude of environmental change cues applied. We also discuss the need to design experiments that are able to distinguish TGP from selection and TGP from WGP in multigenerational experiments. We conclude by suggesting future research directions that build on the knowledge to date and admit the limitations that exist, which will depend on the way environmental change is simulated and the type of experimental design used. Such an approach will open up this burgeoning area of research to a wider variety of organisms and allow better predictive capacity of the role of TGP in the response of organisms to future climate change.

Description: Anthropogenic activities are driving rapid changes in aquatic environments. Numerous studies suggest that climatic shifts and anomalies will convey severe consequences for ecosystems worldwide, leading to disruptions in key processes within populations including larval development, individual growth, and reproductive success. This is further exacerbated by the negative impacts on between-species interactions, and changes to biodiversity and ecosystem services (Munday et al., 2013). Understanding the responses of organisms to environmental shifts is imperative to help predict their fate on a changing planet. Particularly, the capacity of individuals and populations to cope through phenotypic plasticity and adaptation is of critical interest, with advances in genomics and epigenomics techniques helping to unveil the underlying molecular mechanisms (Eirin-Lopez and Putnam, 2019). However, major knowledge gaps remain about the adaptive potential of marine organisms to respond to future ocean conditions. The aim of this Research Topic was to bring together novel research approaches that examine acclimation and adaptation processes in marine organisms, their role in population resilience, and implications for geographical distributions and range shifts under rapid climate change. Contributions to the topic span a broad range of taxa, and investigate a diverse array of response mechanisms such as thermal safety margins (Bennett et al.), thermotolerance via endosymbionts and gene expression (Naugle et al.), tolerance via changes in allele frequencies (Knöbel et al.), local adaptation and maternal effects (Richards et al.), transgenerational plasticity (TGP; Chang et al.), environment-dependent reproductive success (Wanzenböck et al.), and phenological shifts to long-term seasonal changes (Xia et al.). Furthermore, the importance of environmental variability (not only mean changes) at different time scales, the role of developmental or life history stage in phenotypic responses, as well as future challenges for plasticity research (both within and across generations) are outlined in Bautista and Crespel.