Natural volcanic CO2 seeps reveal future trajectories for host–microbial associations in corals and sponges

Atmospheric carbon dioxide (CO2) levels are rapidly rising causing an increase in the partial pressure of CO2 (pCO2) in the ocean and a reduction in pH known as ocean acidification (OA). Natural volcanic seeps in Papua New Guinea expel 99% pure CO2 and thereby offer a unique opportunity to explore the effects of OA in situ. The corals Acropora millepora and Porites cylindrica were less abundant and hosted significantly different microbial communities at the CO2 seep than at nearby control sites <500 m away. A primary driver of microbial differences in A. millepora was a 50% reduction of symbiotic Endozoicomonas. This loss of symbiotic taxa from corals at the CO2 seep highlights a potential hurdle for corals to overcome if they are to adapt to and survive OA. In contrast, the two sponges Coelocarteria singaporensis and Cinachyra sp. were ~40-fold more abundant at the seep and hosted a significantly higher relative abundance of Synechococcus than sponges at control sites. The increase in photosynthetic microbes at the seep potentially provides these species with a nutritional benefit and enhanced scope for growth under future climate scenarios (thus, flexibility in symbiosis may lead to a larger niche breadth). The microbial community in the apparently pCO2-sensitive sponge species S. massa was not significantly different between sites. These data show that responses to elevated pCO2 are species-specific and that the stability and flexibility of microbial partnerships may have an important role in shaping and contributing to the fitness and success of some hosts.

Continue reading ‘Natural volcanic CO2 seeps reveal future trajectories for host–microbial associations in corals and sponges’

Aragonite undersaturation in Gwangyang Bay, South Korea: Effects of fresh water input

Dissolved inorganic carbon (DIC) and alkalinity were precisely measured for surface and bottom waters in Gwangyang Bay, Korea, during the four seasons to assess seasonal variations of aragonite saturation state (Ωarag). Both the surface and bottom waters were undersaturated with respect to aragonite during summer but were supersaturated during the other seasons. The summertime undersaturation of the surface waters with respect to aragonite may have been a result of the dilution effect caused by higher seasonal river runoff. In the bottom waters, the average DIC concentration increased by 40.6 μmol kg™1 from spring to summer, while the average alkalinity decreased by 74.7 μeq kg™1. As a result, the alkalinity/DIC ratio decreased from 1.07 in spring to 1.01 in summer and pH also decreased from 7.91 to 7.48, which resulted in the summertime undersaturation of the bottom waters.

Continue reading ‘Aragonite undersaturation in Gwangyang Bay, South Korea: Effects of fresh water input’

Best practices for autonomous measurement of seawater pH with the Honeywell Durafet

Performance of autonomous pH sensors is evaluated by comparing in situ data to independent bench-top measurements of pH and to co-located pH, O2, and View the MathML sourcepCO2 sensors. While the best practice is always to deploy a properly calibrated sensor, the lengthy time period required for sensor conditioning and calibration often results in sensor deployment without comprehensive calibration. Quality control (QC) procedures are examined to determine the errors associated with different in situ calibration approaches and lay a framework for best practices. Sensor packages employing the Honeywell Durafet remained stable across multiple deployments for over nine months. However, sensor performance was often limited by biofouling. Regional empirical relationships for estimating carbonate system parameters are shown to enable identification of otherwise indistinguishable sensor offset and drift when multiple sensor types are co-located. Uncertainty is determined by calibration approach and must be quantified on a case-by-case basis. Our results indicate that the Durafet is capable of accuracy, relative to a chosen reference, of better than 0.03 pH units over multiple months. Accuracy is improved when a robust shore-side calibration is performed, an independent means of QC is available throughout a deployment, and effective biofouling prevention measures are taken.

Continue reading ‘Best practices for autonomous measurement of seawater pH with the Honeywell Durafet’

Responses of calcification of massive and encrusting corals to past, present, and near-future ocean carbon dioxide concentrations

In this study, we report the acidification impact mimicking the pre-industrial, the present, and near-future oceans on calcification of two coral species (Porites australiensis, Isopora palifera) by using precise pCO2 control system which can produce acidified seawater under stable pCO2 values with low variations. In the analyses, we performed Bayesian modeling approaches incorporating the variations of pCO2 and compared the results between our modeling approach and classical statistical one. The results showed highest calcification rates in pre-industrial pCO2 level and gradual decreases of calcification in the near-future ocean acidification level, which suggests that ongoing and near-future ocean acidification would negatively impact coral calcification. In addition, it was expected that the variations of parameters of carbon chemistry may affect the inference of the best model on calcification responses to these parameters between Bayesian modeling approach and classical statistical one even under stable pCO2 values with low variations.

Continue reading ‘Responses of calcification of massive and encrusting corals to past, present, and near-future ocean carbon dioxide concentrations’

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’

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Ocean acidification in the IPCC AR5 WG II

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