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Living in a high CO2 world: a global meta-analysis shows multiple trait-mediated fish responses to ocean acidification

Understanding how marine organisms will be affected by global change is of primary importance to ensure ecosystem functioning and nature contributions to people. This study meets the call for addressing how life-history traits mediate effects of ocean acidification on fish. We built a database of overall and trait-mediated responses of teleost fish to future CO2 levels by searching the scientific literature. Using a meta-analytical approach, we investigated the effects of projected CO2 levels by IPCC for 2050-2070 and 2100 on fish eco-physiology and behavior from 320 contrasts on 42 species, stemming from polar to tropical regions. Moreover, since organisms may experience a mosaic of carbonate chemistry in coastal environments (e.g., in estuaries, upwelling zones and intertidal habitats), which may have higher pCO(2) values than open ocean waters, we assessed responses from additional 103 contrasts on 21 fish species using pCO(2) levels well above IPCC projections. Under mid-century and end-of-century CO2 emission scenarios, we found multiple CO2-dose-dependent effects on calcification, resting metabolic rate, yolk, and behavioral performances, along with increased predation risk and decreased foraging, particularly for larvae. Importantly, many of the traits considered will not confer fish tolerance to elevated CO2 and far-reaching ecological consequences on fish population replenishment and community structure will likely occur. Extreme CO2 levels well above IPCC projections showed effects on fish mortality and calcification, while growth, metabolism, and yolk were unaffected. CO2 exposures in short-term experiments increased fish mortality, which in turn decreased in longer-term exposures. Whatever the elevated CO2 levels considered, some key biological processes (e.g., reproduction, development, habitat choice) were critically understudied. Fish are an important resource for livelihoods in coastal communities and a key component for stability of marine ecosystems. Given the multiple trait-mediated effects evidenced here, we stress the need to fill the knowledge gap on important eco-physiological processes and to expand the number and duration of ocean acidification studies to multi-generational, multiple stressor (e.g., warming, hypoxia, fishing), and species interactions experiments to better elucidate complex ecosystem-level changes and how these changes might alter provisioning of ecosystem services.

Continue reading ‘Living in a high CO2 world: a global meta-analysis shows multiple trait-mediated fish responses to ocean acidification’

Potential ecotoxicological effects of elevated bicarbonate ion concentrations on marine organisms


• Ecotoxicological effects of elevated DIC were evaluated using 10 marine organisms.
• Species-specific toxicity of elevated DIC were found with EC50 of 11–85 mM.
• Mortality for copepod T. japonicus was the most sensitive endpoint for DIC toxicity.
• Tentative criteria of DIC for protecting 80% of marine organisms is 11 mM.


Recently, a novel method for carbon capture and storage has been proposed, which converts gaseous CO2 into aqueous bicarbonate ions (HCO3-), allowing it to be deposited into the ocean. This alkalinization method could be used to dispose large amounts of CO2 without acidifying seawater pH, but there is no information on the potential adverse effects of consequently elevated HCO3- concentrations on marine organisms. In this study, we evaluated the ecotoxicological effects of elevated concentrations of dissolved inorganic carbon (DIC) (max 193 mM) on 10 marine organisms. We found species-specific ecotoxicological effects of elevated DIC on marine organisms, with EC50-DIC (causing 50% inhibition) of 11-85 mM. The tentative criteria for protecting 80% of individuals of marine organisms are suggested to be pH 7.8 and 11 mM DIC, based on acidification data previously documented and alkalinization data newly obtained from this study. Overall, the results of this study are useful for providing baseline information on ecotoxicological effects of elevated DIC on marine organisms. More complementary studies are needed on the alkalinization method to determine DIC effects on seawater chemistry and marine organisms.

Continue reading ‘Potential ecotoxicological effects of elevated bicarbonate ion concentrations on marine organisms’

What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?

Previous work has not led to a clear understanding of the causes of spatial pattern in global surface ocean DIC, which generally increases polewards. Here, we revisit this question by investigating the drivers of observed latitudinal gradients in surface salinity-normalized DIC (nDIC) using the Global Ocean Data Analysis Project Version 2 (GLODAPv2) database. We used the database to test three different hypotheses for the driver producing the observed increase in surface nDIC from low to high latitudes. These are: (1) sea surface temperature, through its effect on the CO2 system equilibrium constants, (2) salinity-related total alkalinity (TA), and (3) high latitude upwelling of DIC- and TA-rich deep waters. We find that temperature and upwelling are the two major drivers. TA effects generally oppose the observed gradient, except where higher values are introduced in upwelled waters. Temperature-driven effects explains the majority of the surface nDIC latitudinal gradient (182 out of 223μmolkg−1 in the high-latitude Southern Ocean). Upwelling, which has not previously been considered as a major driver, additionally drives a substantial latitudinal gradient. Its immediate impact, prior to any induced air-sea CO2 exchange, is to raise Southern Ocean nDIC by 208μmolkg−1 above the average low latitude value. However, this immediate effect is transitory. The long-term impact of upwelling (brought about by increasing TA), which would persist even if gas exchange were to return the surface ocean to the same CO2 as without upwelling, is to increase nDIC by 74μmolkg−1 above the low latitude average.

Continue reading ‘What drives the latitudinal gradient in open ocean surface dissolved inorganic carbon concentration?’

Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2

The ecological consequences of ocean acidification are unclear due to varying physiological properties of macroalgae and species-specific responses. Therefore, in the present study, we used a laboratory culture experiment to analyse the eco-physiological responses of the Mediterranean subtidal red alga Peyssonnelia squamaria to CO2-induced lower pH. Our results showed an increase in the photosynthetic performance and growth rate of P. squamaria, despite the reduction in CaCO3 content in the low pH treatment. According to our results, we believe that samples exposed to elevated CO2 could be regulated own nitrogen metabolism to support increased growth rate and it may be down-regulated nitrate uptake. As a result, we hypothesize that P. squamaria may benefit from ocean acidification.

Continue reading ‘Physiological responses of the Mediterranean subtidal alga Peyssonnelia squamaria to elevated CO2’

Identifying important species that amplify or mitigate the interactive effects of human impacts to marine food webs

Some species may be more important in transferring the complex effects of multiple human stressors through marine food‐webs. Here we show a novel approach to help inform conservation management in identifying such species. Simulating changes in biomass between species from the interaction effects of ocean warming and ocean acidification, and fisheries to year 2050 on the south‐eastern Australian marine system, we constructed annual interaction effect networks (IEN’s). Each IEN was composed of the species linked by either an additive (sum of the individual stressor response), synergistic (lower biomass compared with additive effects) or antagonistic (greater biomass compared with additive effects) response. Structurally, over the simulation period, the number of species and links in the synergistic IEN’s increased and the network structure became more stable. The stability of the antagonistic IEN’s decreased and became more vulnerable to the loss of species. In contrast, there was no change in the structural attributes of species linked by an additive response. Using indices of species importance common in food‐web and network theory, we identified the most important species within each IEN for transferring the interaction stressor effect on changes in biomass via local, intermediate and global interaction pathways. Mid trophic level mesopelagic fish species were most often identified as the key species within the synergistic IEN’s and phytoplankton or zooplankton within the antagonistic IEN’s. For the additive response commonly assumed in conservation management demersal fish species were identified by all of the indices. Apart from identifying the most important species, we also identified other important species for transferring the different interaction effects. Knowing the most important species for transferring synergistic or antagonistic responses may help inform conservation strategies for conserving ecosystems under increasing multiple stressor impacts.

Continue reading ‘Identifying important species that amplify or mitigate the interactive effects of human impacts to marine food webs’

Calcification of an estuarine coccolithophore increases with ocean acidification when subjected to diurnally fluctuating carbonate chemistry

Ocean acidification has the capacity to impact future coccolithophore growth, photosynthesis, and calcification, but experimental culture work with coccolithophores has produced seemingly contradictory results and has focused on open-ocean species. We investigated the influence of pCO2 (between 250 and 750 µatm) on the growth, photosynthetic, and calcification rates of the estuarine coccolithophore Pleurochrysis carterae using a CO2 manipulation system that allowed for natural carbonate chemistry variability, representing the highly variable carbonate chemistry of coastal and estuarine waters. We further considered the influence of pCO2 on dark calcification. Increased pCO2 conditions had no significant impact on P. carterae growth rate or photosynthetic rate. However, P. carterae calcification rates significantly increased at elevated mean pCO2 concentrations of 750 µatm. P. carterae calcification was somewhat, but not completely, light-dependent, with increased calcification rates at elevated mean pCO2 conditions in both light and dark incubations. This trend of increased calcification at higher pCO2 conditions fits into a recently developed substrate-inhibitor concept, which demonstrates a calcification optima concept that broadly fits the experimental results of many studies on the impact of increased pCO2 on coccolithophore calcification.

Continue reading ‘Calcification of an estuarine coccolithophore increases with ocean acidification when subjected to diurnally fluctuating carbonate chemistry’

Living costs of ocean acidification and warming in herbivorous gastropods and their adaptations

Over the last century, atmospheric concentration of carbon dioxide (pCO₂) has been increasing at an unprecedented rate due to anthropogenic CO₂ emission. The elevated pCO₂ is predicted to cause substantial abiotic changes in future marine ecosystems, including ocean acidification and warming. In addition, extreme climatic events, such as heatwaves, will become more prevalent and persistent due to global warming. Thus, extensive studies have been conducted to determine how ocean acidification and warming affect marine organisms. It is generally considered that these climate change stressors will cause adverse effects on many marine organisms and hence disrupt ecosystem functioning in future. This prediction is, however, largely based on short-term experiments with simple experimental design that may have overestimated the impacts of climate change stressors. In fact, growing evidence shows that some marine organisms can acclimate to the predicted seawater conditions. Therefore, this thesis aims to examine the impacts of ocean acidification and warming on marine organisms and their potential adaptations. Herbivorous gastropods from intertidal to subtidal zones were chosen as the study animals in view of their substantial contribution to herbivory in their habitat. Ocean acidification and warming can raise the energy demand of marine organisms, impacting their energy budget and ultimately survival. After a prolonged exposure period, I found that ocean acidification has limited effect on the energy budget and survival of subtidal gastropods (Thalotia conica and Phasianella australis), suggesting that they are able to cope with the elevated energy demand under ocean acidification. This response can be mediated indirectly by the positive effect of CO₂ enrichment on the nutritional quality (energy content and C:N ratio) of primary producers, which in turn boosts the energy gain of gastropods. In contrast, I found that ocean warming reduces the energy budget, growth and survival of these subtidal gastropods at temperature below their thermal tolerance, implying that prolonged exposure to sublethal thermal stress (e.g. persistent heatwaves) can already threaten their populations.

Continue reading ‘Living costs of ocean acidification and warming in herbivorous gastropods and their adaptations’

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Ocean acidification in the IPCC AR5 WG II

OUP book