Cold-water corals: acidification harms, warming promotes growth

Because they build their skeletons from calcium carbonate, cold-water corals such as the globally distributed species Lophelia pertusa are considered particularly threatened by ocean acidification. This change in seawater chemistry, caused by the absorption of carbon dioxide (CO2) from the atmosphere, reduces the concentration of carbonate ions. With fewer carbonate ions, calcification becomes more difficult. However, laboratory studies at GEOMAR Helmholtz Centre for Ocean Research Kiel reveal, that a simultaneous increase in water temperatures could help Lophelia pertusa to counteract negative effects of ocean acidification. The experiments that were conducted as part of the German research programme on ocean acidification BIOACID (Biological Impacts of Ocean Acidification) demonstrate how important it is to investigate Lophelia’s response to single drivers of climate change as well as their combined effects.

On an expedition with the research vessel POSEIDON and the submersible JAGO, marine biologists from GEOMAR collected corals at Trondheim Fjord (Norway) for their investigations. “During our JAGO dives, we examined the condition of the reefs. We documented their expansion and the diverse community living in the reefs and carefully chose our samples”, explains Janina Büscher. The PhD student from the department of Biological Oceanography at GEOMAR conducted the experiments and is lead author of a publication on the effects and impact of ocean acidification and warming on the growth and fitness of Lophelia pertusa in the research journal Frontiers in Marine Science. “The richness in species of these reefs that exist in almost complete darkness and at temperatures below ten degrees Celsius is very impressive.” Many of these underwater oases, grown over centuries, are protected as natural heritages. Their diversity ensures the resilience of the fjord ecosystem, and many species of fish find shelter and food in the reefs.

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Rising carbon dioxide levels, ocean acidity may change crucial marine process

Climate change may be putting cyanobacteria that are crucial to the functioning of the ocean at risk as the amount of carbon dioxide in the atmosphere increases and the acidity of ocean water changes.

In a paper published Thursday in Science, a team of researchers from Florida State University, Xiamen University in China and Princeton University argue that the acidification of seawater caused by rising carbon dioxide levels makes it difficult for a type of cyanobacteria to perform a process called nitrogen fixation.

Few people know much about a type of cyanobacteria called Trichodesmium, but this miniscule collection of cells is critical to the health of hundreds of species in the Earth’s oceans. Through nitrogen fixation, Trichodesmium converts nitrogen gas into ammonia and other molecules that organisms are dependent on for survival.

Trichodesmium is thought to be responsible for about 50 percent of marine nitrogen fixation, so a decline in its ability could have a major ripple effect on marine ecosystems.

“This is one of the major sources of nitrogen for other organisms in the open ocean,” said Sven Kranz, assistant professor of Earth, Ocean and Atmospheric Science at Florida State University and a co-author of this study. “If Trichodesmium responds negatively to the environmental changes forced upon the ocean by fossil fuel burning, it could have a large effect on our food web.”

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Ocean warming to cancel increased CO2-driven productivity

University of Adelaide researchers have constructed a marine food web to show how climate change could affect our future fish supplies and marine biodiversity.

Published today in Global Change Biology, the researchers found that high CO2 expected by the end of the century which causes ocean acidification will boost production at different levels of the food web, but ocean warming cancelled this benefit by causing stress to marine animals, preventing them using the increased resources efficiently for their own growth and development. The result was a collapsing food web.

“Humans rely heavily on a diversity of services that are provided by ocean ecosystems, including the food we eat and industries that arise from that,” says project leader Professor Ivan Nagelkerken, from the University’s Environment Institute.

“Our understanding of what’s likely to happen has been hampered by an over-reliance on simplified laboratory systems centred on single levels of the food web. In this study, we created a series of three-level food webs and monitored and measured the results over a number of months to provide an understanding of future food webs under climate change.”

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Boosted food web productivity through ocean acidification collapses under warming

Future climate is forecast to drive bottom-up (resource driven) and top-down (consumer driven) change to food web dynamics and community structure. Yet, our predictive understanding of these changes is hampered by an over-reliance on simplified laboratory systems centred on single trophic levels. Using a large mesocosm experiment, we reveal how future ocean acidification and warming modify trophic linkages across a three-level food web: that is, primary (algae), secondary (herbivorous invertebrates) and tertiary (predatory fish) producers. Both elevated CO2 and elevated temperature boosted primary production. Under elevated CO2, the enhanced bottom-up forcing propagated through all trophic levels. Elevated temperature, however, negated the benefits of elevated CO2 by stalling secondary production. This imbalance caused secondary producer populations to decline as elevated temperature drove predators to consume their prey more rapidly in the face of higher metabolic demand. Our findings demonstrate how anthropogenic CO2 can function as a resource that boosts productivity throughout food webs, and how warming can reverse this effect by acting as a stressor to trophic interactions. Understanding the shifting balance between the propagation of resource enrichment and its consumption across trophic levels provides a predictive understanding of future dynamics of stability and collapse in food webs and fisheries production.

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The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium

Acidification of seawater caused by anthropogenic carbon dioxide (CO2) is anticipated to influence the growth of dinitrogen (N2)–fixing phytoplankton, which contribute a large fraction of primary production in the tropical and subtropical ocean. We found that growth and N2-fixation of the ubiquitous cyanobacterium Trichodesmium decreased under acidified conditions, notwithstanding a beneficial effect of high CO2. Acidification resulted in low cytosolic pH and reduced N2-fixation rates despite elevated nitrogenase concentrations. Low cytosolic pH required increased proton pumping across the thylakoid membrane and elevated adenosine triphosphate production. These requirements were not satisfied under field or experimental iron-limiting conditions, which greatly amplified the negative effect of acidification.

Continue reading ‘The complex effects of ocean acidification on the prominent N2-fixing cyanobacterium Trichodesmium’

Coordination Meeting on Standardized Methodology and Networking to Address Ocean Acidification takes place in Vienna

Ocean acidification poses a growing challenge to marine organisms and ecosystems and therefore also to many countries relying on marine resources. Research on this topic, which is affecting Member States all around the globe has been evolving continuously, however still lacks general public awareness. To build awareness of ocean acidification and to encourage collaboration between Member States, the IAEA held a meeting in Vienna, Austria, from 10 to 12 April. Twenty-seven countries attended the meeting, including Algeria, Argentina, Bangladesh, Belize, Brazil, Cambodia, Cameroon, Chile, China, Cuba, Ecuador, Egypt, Guatemala, Iraq, Kenya, Kuwait, Madagascar, Marshall Islands, Mexico, Namibia, Palau, Peru, Philippines, Slovenia, Thailand and Turkey.  The meeting, organized under an interregional IAEA technical cooperation (TC) project1/, aimed to allow counterparts to present their work, capacities and needs, based on a questionnaire circulated earlier in the year. In addition, possibilities for regional and interregional collaboration were explored, and participants discussed data sharing and management efforts, as well as data synthesis products, gaps in capacity building, and possible outreach activities. Project work plans were adapted accordingly.

IAEA technical cooperation support through the interregional project aims to foster collaboration and coordination among participating Member States, and to start a discourse with other interested countries and parties. The overall goal of the project is to help build capacity to measure and study ocean acidification, and to connect countries and regions with an interest in this emerging environmental problem. The project aims to promote standardization of methodology, and to support and encourage capacity building, regional and inter-regional networking, collaboration and data sharing, and outreach to key stakeholders.

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Can seaweed farming play a role in climate change mitigation and adaptation?

Seaweed aquaculture, the fastest-growing component of global food production, offers a slate of opportunities to mitigate, and adapt to climate change. Seaweed farms release carbon that maybe buried in sediments or exported to the deep sea, therefore acting as a CO2 sink. The crop can also be used, in total or in part, for biofuel production, with a potential CO2 mitigation capacity, in terms of avoided emissions from fossil fuels, of about 1,500 tons CO2 km−2 year−1. Seaweed aquaculture can also help reduce the emissions from agriculture, by improving soil quality substituting synthetic fertilizer and when included in cattle fed, lowering methane emissions from cattle. Seaweed aquaculture contributes to climate change adaptation by damping wave energy and protecting shorelines, and by elevating pH and supplying oxygen to the waters, thereby locally reducing the effects of ocean acidification and de-oxygenation. The scope to expand seaweed aquaculture is, however, limited by the availability of suitable areas and competition for suitable areas with other uses, engineering systems capable of coping with rough conditions offshore, and increasing market demand for seaweed products, among other factors. Despite these limitations, seaweed farming practices can be optimized to maximize climate benefits, which may, if economically compensated, improve the income of seaweed farmers.

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Ocean acidification in the IPCC AR5 WG II

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