Sheltering habits help sharks cope with acid oceans

A shark’s habitat can reduce its sensitivity to rising CO2 levels, according to Australian scientists.

Globally, ocean acidification – linked to emissions of greenhouse gases – remains a major concern and scientists say it will harm many marine species over the next century.

Researchers from the ARC Centre of Excellence for Coral Reef Studies (Coral CoE) at James Cook University have found that the epaulette shark, a species that shelters within reefs and copes with low oxygen levels, is able to tolerate increased carbon dioxide in the water without any obvious physical impact.

“As part of the study we exposed the sharks to increased CO2 for more than two months, mirroring the levels predicted for the end of the century,” says study co-author Dr Jodie Rummer from Coral CoE.

Continue reading ‘Sheltering habits help sharks cope with acid oceans’

A product of its environment: the epaulette shark (Hemiscyllium ocellatum) exhibits physiological tolerance to elevated environmental CO2

Ocean acidification, resulting from increasing anthropogenic CO2 emissions, is predicted to affect the physiological performance of many marine species. Recent studies have shown substantial reductions in aerobic performance in some teleost fish species, but no change or even enhanced performance in others. Notably lacking, however, are studies on the effects of near-future CO2 conditions on larger meso and apex predators, such as elasmobranchs. The epaulette shark (Hemiscyllium ocellatum) lives on shallow coral reef flats and in lagoons, where it may frequently encounter short-term periods of environmental hypoxia and elevated CO2, especially during nocturnal low tides. Indeed, H. ocellatum is remarkably tolerant to short periods (hours) of hypoxia, and possibly hypercapnia, but nothing is known about its response to prolonged exposure. We exposed H. ocellatum individuals to control (390 µatm) or one of two near-future CO2 treatments (600 or 880 µatm) for a minimum of 60 days and then measured key aspects of their respiratory physiology, namely the resting oxygen consumption rate, which is used to estimate resting metabolic rate, and critical oxygen tension, a proxy for hypoxia sensitivity. Neither of these respiratory attributes was affected by the long-term exposure to elevated CO2. Furthermore, there was no change in citrate synthase activity, a cellular indicator of aerobic energy production. Plasma bicarbonate concentrations were significantly elevated in sharks exposed to 600 and 880 µatm CO2 treatments, indicating that acidosis was probably prevented by regulatory changes in acid–base relevant ions. Epaulette sharks may therefore possess adaptations that confer tolerance to CO2 levels projected to occur in the ocean by the end of this century. It remains uncertain whether other elasmobranchs, especially pelagic species that do not experience such diurnal fluctuations in their environment, will be equally tolerant.

Continue reading ‘A product of its environment: the epaulette shark (Hemiscyllium ocellatum) exhibits physiological tolerance to elevated environmental CO2′

New report says more effort needed to help combat ocean acidification

The federal government needs to pay more attention to what is often referred to as “the other carbon dioxide problem” – the acidification of the oceans – to help stave off widespread damage to seafood, tourism and storm protection, according to a new federal report.

The report from the Government Accountability Office, Congress’ watchdog, concluded that federal officials have made some progress implementing a 2009 law on acidification. But they haven’t done enough.

For example, the GAO said, an interagency working group chaired by the Department of Commerce’s National Oceanic and Atmospheric Administration, has been established, as required. And it has developed a research and monitoring plan that outlines steps to better understand ocean acidification. But the agencies involved have yet to implement several of the law’s requirements, including those dealing with the budget necessary to implement a research and monitoring plan.

Continue reading ‘New report says more effort needed to help combat ocean acidification’

Effects of ocean acidification combined with hypoxia, elevated temperature, or restricted food supply on early life stages of the forage fish Menidia beryllina, Menidia menidia, and Cyprinodon variegatus

Estuarine organisms are experiencing many stressors related to climate change at an accelerated pace when compared to the open ocean. The co-occurrence of acidification and hypoxia has been observed during warmer months when many fish species spawn in temperate estuaries. Concurrently, estuarine systems can experience extreme temperatures during summer and dynamic levels of plankton. This study assessed the tolerance of early life stage estuarine fish to the co-occurrence of acidification with hypoxia, elevated temperatures, and varying levels of planktonic prey. Time to hatch, hatching rates, survival, and growth were quantified for larval Menidia beryllina, Menidia menidia, and Cyprinodon variegatus exposed from the egg through the larval stages to water with a low pH (7.4 versus 7.9, total scale) and dissolved oxygen concentration (2.5 mg L-1 versus 9.0 mg L-1), while embryos of M. beryllina were also exposed to elevated temperatures and varying levels of prey. Hypoxia significantly delayed hatching of embryos by one to three days and reduced hatching success of all three species by 24 – 80%. Acidification and hypoxia had an additive negative effect on survival of M. beryllina, a synergistic negative effect on survival of M. menidia spawned in May but not June, and no effect on survival of C. variegatus. Acidification and hypoxia had an additive negative effect on length of larval M. beryllina while hypoxia alone significantly reduced length of M. menidia and C. variegatus, with reductions ranging from 15–45%. As abundant forage fish in estuaries along the Atlantic coast of the US, the tolerance of these three species to acidification and hypoxia may strongly influence the success of the coastal ecosystems and fisheries that depend on them as prey. Acidification and restricted food each significantly reduced survival (by 26% and 33%, respectively) and length (by 15% and 20%) of M. beryllina, and when combined they had an additive negative effect on survival and an antagonistic effect on length. Acidification and elevated temperature each significantly reduced survival (by 18% and 85%, respectively) of M. beryllina while the combined stressors had an antagonistic effect. This study contributes to the growing body of research that aims to predict how multiple climate change stressors will affect marine organisms and, in turn, ocean ecosystems.

Continue reading ‘Effects of ocean acidification combined with hypoxia, elevated temperature, or restricted food supply on early life stages of the forage fish Menidia beryllina, Menidia menidia, and Cyprinodon variegatus’

Ocean acidification: federal response under way, but actions needed to understand and address potential impacts

What GAO found

Ocean acidification could have a variety of potentially significant effects on marine species, ecosystems, and coastal communities, according to six summary reports that GAO reviewed. The reports were developed by federal agencies and others and were based on extensive reviews of the scientific literature. The scientific understanding of these effects, however, is still developing, and uncertainty remains about their scope and severity. Potential effects of ocean acidification include:

Reducing the ability of some marine species, such as oysters, to form shells or altering their physiology or behavior. These impacts could affect some species’ growth and survival.

Altering marine ecosystems, for example, by disrupting predator and prey relationships in food webs and altering habitats.

Disrupting the economy or culture of some communities, for example, by harming coastal fishing and tourism industries.

Continue reading ‘Ocean acidification: federal response under way, but actions needed to understand and address potential impacts’

Coral reefs (in IPCC 2014 Report)

Coral reefs are shallow-water ecosystems that consist of reefs made of calcium carbonate which is mostly secreted by reef-building corals and encrusting macroalgae. They occupy less than 0.1%
of the ocean floor yet play multiple important roles throughout the tropics, housing high levels of biological diversity as well as providing key ecosystem goods and services such as habitat for fisheries, coastal protection, and appealing environments for tourism (Wild et al., 2011). About 275 million people live within 30 km of a coral reef (Burke et al., 2011) and derive some benefits from the ecosystem services that coral reefs provide (Hoegh-Guldberg, 2011), including provisioning (food, livelihoods, construction material, medicine), regulating (shoreline protection, water quality), supporting (primary production, nutrient cycling), and cultural (religion, tourism) services. This is especially true for the many coastal and small island nations in the world’s tropical regions. (…)

Continue reading ‘Coral reefs (in IPCC 2014 Report)’

Ocean acidification (in IPCC 2014 Report)

Anthropogenic ocean acidification and global warming share the same primary cause, which is the increase of atmospheric CO2 (Figure OA-1A; WGI, Section 2.2.1). Eutrophication, loss of sea ice, upwelling and deposition of atmospheric nitrogen and sulfur all exacerbate ocean acidification locally. Chemistry and Projections The fundamental chemistry of ocean acidification is well understood (robust evidence, high agreement). Increasing atmospheric concentrations of CO2 result in an increased flux of CO2 into a mildly alkaline ocean, resulting in a reduction in pH, carbonate ion concentration, and the capacity of seawater to buffer changes in its chemistry (very high confidence). The changing chemistry of the surface layers of the open ocean can be projected at the global scale with high accuracy using projections of atmospheric CO2 levels (Figure CC-OA-1B). Observations of changing upper ocean CO2 chemistry over time support this linkage (WGI Table 3.2 and Figure 3.18; Figures 30-8, 30-9). Projected changes in open ocean, surface water chemistry for the year 2100 based on representative concentration pathways (WGI, Figure 6.28) compared to pre-industrial values range from a pH change of –0.14 units with Representative Concentration Pathway (RCP)2.6 (421 ppm CO2, +1°C, 22% reduction of carbonate ion concentration) to a pH change of –0.43 units with RCP8.5 (936 ppm CO2, +3.7ºC, 56% reduction of carbonate ion concentration). Projections of regional changes, especially in the highly complex coastal systems (Sections 5.3.3.5, 30.3.2.2), in polar regions (WGI Section 6.4.4), and at depth are more difficult but generally follow similar trends. (…) Continue reading ‘Ocean acidification (in IPCC 2014 Report)’


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Ocean acidification in the IPCC AR5 WG II

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