Stable photosymbiotic relationship under CO2-induced acidification in the acoel worm Symsagittifera roscoffensis

As a consequence of anthropogenic CO₂ emissions, oceans are becoming more acidic, a phenomenon known as ocean acidification. Many marine species predicted to be sensitive to this stressor are photosymbiotic, including corals and foraminifera. However, the direct impact of ocean acidification on the relationship between the photosynthetic and nonphotosynthetic organism remains unclear and is complicated by other physiological processes known to be sensitive to ocean acidification (e.g. calcification and feeding). We have studied the impact of extreme pH decrease/pCO₂ increase on the complete life cycle of the photosymbiotic, non-calcifying and pure autotrophic acoel worm, Symsagittifera roscoffensis. Our results show that this species is resistant to high pCO₂ with no negative or even positive effects on fitness (survival, growth, fertility) and/or photosymbiotic relationship till pCO₂ up to 54 K µatm. Some sub-lethal bleaching is only observed at pCO₂ up to 270 K µatm when seawater is saturated by CO₂. This indicates that photosymbiosis can be resistant to high pCO₂. If such a finding would be confirmed in other photosymbiotic species, we could then hypothesize that negative impact of high pCO₂ observed on other photosymbiotic species such as corals and foraminifera could occur through indirect impacts at other levels (calcification, feeding).

History of seawater carbonate chemistry, atmospheric CO2, and ocean acidification

Humans are continuing to add vast amounts of carbon dioxide (CO₂) to the atmosphere through fossil fuel burning and other activities. A large fraction of the CO₂ is taken up by the oceans in a process that lowers ocean pH and carbonate mineral saturation state. This effect has potentially serious consequences for marine life, which are, however, difficult to predict. One approach to address the issue is to study the geologic record, which may provide clues about what the future holds for ocean chemistry and marine organisms. This article reviews basic controls on ocean carbonate chemistry on different timescales and examines past ocean chemistry changes and ocean acidification events during various geologic eras. The results allow evaluation of the current anthropogenic perturbation in the context of Earth’s history. It appears that the ocean acidification event that humans are expected to cause is unprecedented in the geologic past, for which sufficiently well-preserved records are available.

Large-scale stress factors affecting coral reefs: open ocean sea surface temperature and surface seawater aragonite saturation over the next 400 years

One-third of the world’s coral reefs have disappeared over the last 30 years, and a further third is under threat today from various stress factors. The main global stress factors on coral reefs have been identified as changes in sea surface temperature (SST) and changes in surface seawater aragonite saturation (Ω_arag). Here, we use a climate model of intermediate complexity, which includes an ocean general circulation model and a fully coupled carbon cycle, in conjunction with present-day observations of inter-annual SST variability to investigate three IPCC representative concentration pathways (RCP 3PD, RCP 4.5, and RCP 8.5), and their impact on the environmental stressors of coral reefs related to open ocean SST and open ocean Ω_arag over the next 400 years. Our simulations show that for the RCP 4.5 and 8.5 scenarios, the threshold of 3.3 for zonal and annual mean Ω_arag would be crossed in the first half of this century. By year 2030, 66–85% of the reef locations considered in this study would experience severe bleaching events at least once every 10 years. Regardless of the concentration pathway, virtually every reef considered in this study (>97%) would experience severe thermal stress by year 2050. In all our simulations, changes in surface seawater aragonite saturation lead changes in temperatures.

Climate change, tipping elements and security

Climate change is increasingly being described as a threat to international (as well as ‘human’) security. We examine the claim that it is the so-called ‘tipping elements’ of the Earth System which constitute the most important threats. Three examples of suggested tipping elements, (1) de-stabilization of the West-Antarctic Ice Cap, (2) acidifi cation of the upper layers of the ocean and (3) die-back of the Amazon rain forest, are used to illustrate the ways in which tipping elements may cause insecurity, in various meanings of the term. Further, the use of the tipping element/point metaphor as a means of communicating the risks and uncertainties associated with climate change is discussed, and it is compared to the alternative terminology used by IPCC. Subsequently, we discuss the extent to which the use of the tipping element/point metaphor constitutes ‘securitization’ of climate change, and whether or not such securitization, in ‘hard’ or ‘soft’ versions, is desirable. It is concluded that while ‘hard securitization’, presumably involving use of force, is unlikely to be relevant, ‘soft securitization’ may be realistic – and even necessary – in order to mobilize the reform of international political institutions required to deal effi ciently with climate change in general and tipping elements specifi cally.

Puget Sound, under threat from ocean acidification, put on ‘Waters of concern’ list

In its water-quality report to the Environmental Protection Agency, the state of Washington classified the entire Puget Sound as “waters of concern” because of ocean acidification’s threat to local shellfish and fish resources. This means the data show that ocean acidification is threatening the region’s ability to support fish and shellfish. It also makes the area a priority for more monitoring and assessment.

“Ocean acidification is putting the whole Puget Sound ecosystem at risk,” said Miyoko Sakashita, oceans director at the Center for Biological Diversity. “Focusing on the entire Sound as a ‘water of concern’ because of ocean acidification is a key step toward monitoring the effects of this sea change and curbing those effects.”

PhD opportunity: Coral reef adaptation strategies to carbonate chemistry changes along the Costa Rican Pacific coast

This project addresses the issue of ocean acidification caused by anthropogenic emissions of CO₂ in the atmosphere. Many experiments have shown that calcification of scleractinian corals declines with increasing CO₂ concentration. The Costa Rican Pacific coast is partly affected by corrosive waters that well up along the coast and periodically expose reefs to pH values lower than usual and similar to those expected in a high CO₂ world of the future. With this project, we are interested to study the impact of upwelling on the metabolism of calcifying reef organisms and the adaptation of coral reefs to natural changes in seawater chemical composition. The work will be carried out in Costa Rica and in the ZMT laboratories in close cooperation with the Systems Ecology Group, the Carbon and Nutrient Cycle Group of the ZMT, and the University of Costa Rica in San Jose. The appointment is for a three-year period. Salary will be according to the German TV-L 13 for a half-time position.