Posts Tagged 'review'

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’

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?’

Revisiting the larval dispersal black box in the Anthropocene

Many marine organisms have a multi-phase life history and rely on their planktonic larvae for dispersal. Despite the important role of larvae in shaping population distribution and abundance, the chemical, physical, and biological factors that shape larval fate are still not fully understood. Shedding light into this larval dispersal “black box” has become critical in the face of global climate change, primarily due to the importance of larval dispersal in formulating sound conservation and management strategies. Focusing on two major stressors, warming and acidification, we highlight the limitations of the current species-by-species, lab-based study approach, and particularly the lack of consideration of the larval experience along the dispersive pathway. Measuring organismal responses to environmentally relevant climate change stress demands an improved documentation of the physical and biological conditions that larvae experience through ontogeny, which in turn requires updated empirical and theoretical approaches. While there are meaningful between taxa comparisons to be made by larval ecologists, to peek into the dispersal black box and to investigate the larger scale consequences of altered dispersal requires innovative collaborations between ecologists, oceanographers, molecular biologists, statisticians, and mathematicians.

Continue reading ‘Revisiting the larval dispersal black box in the Anthropocene’

Decline in symbiont densities of tropical and subtropical scleractinian corals under ocean acidification

Ocean acidification changes the carbonate chemistry of seawater in a manner that reduces the biomineralisation rate of reef-building corals. Other effects of acidification on coral physiology are less well explored, and recent debate has focused on whether ocean acidification causes a change in Symbiodinium densities within tropical and subtropical reef-building corals. Within the framework of null-hypothesis significance testing, some aquaria experiments have provided evidence for a decrease in symbiont densities within coral tissue under ocean acidification (whilst others have suggested an increase). However, null effects have prevailed in the majority of such experiments, and so the question has remained unresolved. This study attempted to resolve this question using a meta-analytic framework, by establishing the effect sizes for symbiont density change under ocean acidification from a structured search of the literature. A regression of effect size (Hedge’s d) versus level of ocean acidification revealed a statistically significant negative relationship, with symbiont density per cm2 decreasing as the level of ocean acidification increased. The decline amounted to an additional 0.07 standard deviations of difference in symbiont density between corals in control (near present day) and acidified seawater with every 100 μatm of increase in partial pressure of CO2 in seawater (a relationship with an r2 of 0.24). A further unresolved question is whether ocean acidification will synergistically exacerbate (or diminish) symbiont density reductions caused by elevated temperature. An analysis of covariance did not reveal a greater decline in symbiont densities with increasing acidification at elevated temperature compared to non-stressful temperature, though this latter analysis should be viewed as exploratory due to a lower sample size. The well-supported evidence for a decline in symbiont densities in tropical and subtropical corals under ocean acidification now provides an impetus for sustained investigation of the consequences of such a change for holobiont functioning and the broader function of the coral reef ecosystem.

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Starfish larvae lose substantial energy to maintain digestion under ocean acidification conditions

A team of researchers led by Marian Hu from the Institute of Physiology in Christian‐Albrechts‐University, Kiel (Germany) investigated the hidden link between ocean acidification (OA) and digestive functions of microscopic marine larvae. The results of this study are presented in this issue of Acta Physiologica [1]. Ocean acidification ‐ a human‐driven global change in ocean pH – is expected to have multiple impacts on the marine ecosystem and its services but also directly on animal physiology. For instance, Hu and colleagues demonstrated that low‐pH seawater treatment strongly affected the metabolism of the brittlestar Amphiura filliformis and even reduced by 80% arm regeneration following amputation [2]. This team became particularly interested in the metabolic costs of maintaining vital functions such as calcification [3] and digestion [4] under acidified seawater conditions, using echinoderm larvae as their model.

Continue reading ‘Starfish larvae lose substantial energy to maintain digestion under ocean acidification conditions’

Oceans: going deep into their past to understand their future

The history of the oceans covers most of the history of Earth, and even more importantly oceans represent the system from which life originated. Eelco Rohling’s new book is a fantastic attempt to impart the knowledge of the oceans to a wide audience. Using erudite yet comprehensible language, the author reports and critically discusses the main events that shaped the story of our planet across time. He believes that the actual knowledge of the oceans is limited to a small group of scientists and that we need to do more to explain the oceans’ mysteries. The palaeoceanographic background of the author helps the reader to learn crucial information on the seas and their history in a simple and convincing manner. This book explains the history of the oceans, from their formation, and helps us to understand their natural evolution and to discriminate natural versus anthropogenic alterations. Approximately 500 years ago, the oceans were still almost completely pristine, but in the 19th century the oceans started to be seriously impacted by the activities of the growing human population, which had reached 1 billion. The anthropogenic impact is multifaceted and profound, and it includes overfishing, pollution, eutrophication, acidification and warming. In the last century, the development of new technologies has enabled marine research to improve our understanding of the effects of such changes. This book provides clear evidence of the role of the oceans in mitigating ongoing global change. The seas and oceans of the world have already absorbed more than a third of the CO 2 that has been produced as a result of human activities. Yet the CO 2 increase is causing a progressive acidification of the oceans, with crucial consequences for marine life. The oceans have also absorbed more than 90% of the heat associated with global warming. The history of the Earth helps us to understand the causes and consequences of such changes.

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Ocean acidification studies and the uncertainties relevance on measurements of marine carbonate system properties

The global ocean has a key role on the Earth’s climate system. It possesses a direct connection with the atmospheric gases, including the greenhouses, allowing exchanges between those compartments and oceanic storage of carbon. Through the years, this exchange of gases occurred based on gas equilibrium between ocean and atmosphere. After the Industrial Revolution, human activities have increased the emissions of greenhouse gases, mainly carbon dioxide (CO2), which changed the atmospheric concentration from ~280 ppm of CO2 to values as high as 391 ppm between c.a. 1750 and 2011 (Ciais et al., 2013). Recently, the measured CO2 atmospheric values are ranging near or above 400 ppm, as recorded by the Mauna Loa observatory, in Hawaii (daily CO2 measurements information available on A regional study in the south-southeast Brazilian continental shelf agrees with this value, which has measured an average of 396.7±2.5 ppm in the atmosphere during the spring of October 2014 (Kerr et al., 2016). This enhancement is reflected in the ocean, which has absorbed about 25% to 30% of the anthropogenic atmospheric CO2 emissions (Sabine and Tanhua, 2010); Le Quére et al., 2016). The CO2 uptake by the oceans directly affects the seawater chemistry and marine biogeochemical processes, impacting both the ecosystems and their respective biota (Doney et al., 2009).

Continue reading ‘Ocean acidification studies and the uncertainties relevance on measurements of marine carbonate system properties’

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Ocean acidification in the IPCC AR5 WG II

OUP book