Posts Tagged 'review'

The rise of CO2 and ocean acidification

Ocean acidification is a closely linked consequence of increasing carbon dioxide (CO2) in the atmosphere, involving multiple changes in seawater chemistry. Observed long-term trends are superimposed on natural variability over a range of space and time scales. The future scale and impacts of ocean acidification depend on how rapidly CO2emissions can be reduced. Although the chemistry of ocean acidification is relatively well understood, effects on marine life, and subsequent socio-economic consequences, remain uncertain. The main biological knowledge gaps relate to genetic adaptation potential, interactions with other stressors (that may also be linked to climate change), and complex ecological interactions associated with competition, species interdependencies, and food webs. Societal impacts are likely to be greatest for human communities that are most reliant directly on marine bioresources, predominantly in coastal areas and small island states.

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Acid–base physiology, neurobiology and behaviour in relation to CO2-induced ocean acidification

Experimental exposure to ocean and freshwater acidification affects the behaviour of multiple aquatic organisms in laboratory tests. One proposed cause involves an imbalance in plasma chloride and bicarbonate ion concentrations as a result of acid–base regulation, causing the reversal of ionic fluxes through GABAA receptors, which leads to altered neuronal function. This model is exclusively based on differential effects of the GABAA receptor antagonist gabazine on control animals and those exposed to elevated CO2. However, direct measurements of actual chloride and bicarbonate concentrations in neurons and their extracellular fluids and of GABAA receptor properties in aquatic organisms are largely lacking. Similarly, very little is known about potential compensatory mechanisms, and about alternative mechanisms that might lead to ocean acidification-induced behavioural changes. This article reviews the current knowledge on acid–base physiology, neurobiology, pharmacology and behaviour in relation to marine CO2-induced acidification, and identifies important topics for future research that will help us to understand the potential effects of predicted levels of aquatic acidification on organisms.

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Autonomous observing platform CO2 data shed new light on the Southern Ocean carbon cycle.

While the number of surface ocean CO2 partial pressure (pCO2) measurements has soared the recent decades, the Southern Ocean remains undersampled. Williams et al. [2017] now present pCO2 estimates based on data from pH-sensor equipped Bio-Argo floats, which have been measuring in the Southern Ocean since 2014. The authors demonstrate the utility of these data for understanding the carbon cycle in this region, which has a large influence on the distribution of CO2 between the ocean and atmosphere. Biogeochemical sensors deployed on autonomous platforms hold the potential to shape our view of the ocean carbon cycle in the coming decades.

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The vulnerability and resilience of reef-building corals

Reef-building corals provide the foundation for the structural and biological diversity of coral-reef ecosystems. These massive biological structures, which can be seen from space, are the culmination of complex interactions between the tiny polyps of the coral animal in concert with its unicellular symbiotic algae and a wide diversity of closely associated microorganisms (bacteria, archaea, fungi, and viruses). While reef-building corals have persisted in various forms for over 200 million years, human-induced conditions threaten their function and persistence. The scope for loss associated with the destruction of coral reef systems is economically, biologically, physically and culturally immense. Here, we provide a micro-to-macro perspective on the biology of scleractinian corals and discuss how cellular processes of the host and symbionts potentially affect the response of these reef builders to the wide variety of both natural and anthropogenic stressors encountered by corals in the Anthropocene. We argue that the internal physicochemical settings matter to both the performance of the host and microbiome, as bio-physical feedbacks may enhance stress tolerance through environmentally mediated host priming and effects on microbiome ecological and evolutionary dynamics.

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Marine paleoclimatic proxies: A shift from qualitative to quantitative estimation of seawater parameters

Understanding past climate during contrasting boundary conditions can help in assessing imminent climate changes. Marine sediments offer a vast archive of past climate. Various indirect methods called proxies are used to infer principal climate parameters like temperature, salinity, productivity, monsoon intensity, ocean circulation, seawater pH, and others, from the marine sediments. The relationship between a climate parameter and marine paleoclimate proxy may vary from region to region. Additionally, the marine proxies are often affected by more than one climate parameter, thus making it difficult to assess the change in any particular parameter from a single proxy. Diagenetic alteration can also significantly affect the parameter-proxy relationship. A growing emphasis now is on quantifying changes in key climatic parameters in the past. Proxies for quantitative estimation of seawater temperature, runoff, sea-level and pH are now fairly well established. Similar robust quantitative proxies for dissolved oxygen concentration and productivity are, however, still being developed. Additionally, the uncertainty associated with quantitative estimation of past climate has to be reduced. Therefore, continuous efforts are being made to develop novel paleoclimate proxies and to evaluate existing proxies in different regions of the world oceans.

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Coral reef ecosystems under climate change and ocean acidification

Coral reefs are found in a wide range of environments, where they provide food and habitat to a large range of organisms as well as providing many other ecological goods and services. Warm-water coral reefs, for example, occupy shallow sunlit, warm, and alkaline waters in order to grow and calcify at the high rates necessary to build and maintain their calcium carbonate structures. At deeper locations (40–150 m), “mesophotic” (low light) coral reefs accumulate calcium carbonate at much lower rates (if at all in some cases) yet remain important as habitat for a wide range of organisms, including those important for fisheries. Finally, even deeper, down to 2,000 m or more, the so-called “cold-water” coral reefs are found in the dark depths. Despite their importance, coral reefs are facing significant challenges from human activities including pollution, over-harvesting, physical destruction, and climate change. In the latter case, even lower greenhouse gas emission scenarios (such as Representative Concentration Pathway RCP 4.5) are likely drive the elimination of most warm-water coral reefs by 2040–2050. Cold-water corals are also threatened by warming temperatures and ocean acidification although evidence of the direct effect of climate change is less clear. Evidence that coral reefs can adapt at rates which are sufficient for them to keep up with rapid ocean warming and acidification is minimal, especially given that corals are long-lived and hence have slow rates of evolution. Conclusions that coral reefs will migrate to higher latitudes as they warm are equally unfounded, with the observations of tropical species appearing at high latitudes “necessary but not sufficient” evidence that entire coral reef ecosystems are shifting. On the contrary, coral reefs are likely to degrade rapidly over the next 20 years, presenting fundamental challenges for the 500 million people who derive food, income, coastal protection, and a range of other services from coral reefs. Unless rapid advances to the goals of the Paris Climate Change Agreement occur over the next decade, hundreds of millions of people are likely to face increasing amounts of poverty and social disruption, and, in some cases, regional insecurity.

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Ocean acidification: an impending disaster to benthic shelled invertebrates and ecosystem

Ocean acidification (OA) is posing a significant threat to marine biodiversity and ecosystem functioning. This review highlights the current state of knowledge and gaps on biological responses of benthic shelled invertebrates to OA. A substantial research accomplished during the last decade demonstrated that the key invertebrates such as corals, oysters, mussels, crustaceans, echinoderms would be severely affected by this phenomenon in the near future. The effects are varied among taxa and life stages within taxa; heavily calcified (mussel, oyster, gastropods) are more sensitive than less calcified invertebrates (crabs, copepods, tanaids), and larval stage are more vulnerable than adult stage. When all taxa are considered together, OA has a significant negative effect on calcification, growth and survival, development and abundance. Most of the studies conducted in vitro for short-term basis using single species and single stressor which may not reflect the real ecosystem scenario. Experiments combining multiple stressors (temperature, hypercapnia, hypoxia, nutrients) have just been initiated. Still, field data at community and ecosystem level are lacking. The variety of biological response observed at the organism level might prevent extrapolation at the community and ecosystem level. Therefore, for improved comprehension of marine ecosystem response to OA needs manipulative experiments on the community level.

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Ocean acidification in the IPCC AR5 WG II

OUP book