Ocean acidification record-high

Sea urchins are harmed by higher levels of copper in the acidified water. Photo: Kirt Edblom/flickr.com/ CC BY-SA

The rate of ocean acidification is the highest in millions of years. A CBD synthesis and new research show a grim picture in which organisms on the sea floor are particularly at risk.

Historically, the ocean has absorbed approximately 30 per cent of all CO₂ released into the atmosphere by humans since the start of the industrial revolution, resulting in a 26 per cent increase in the acidity of the ocean (see AN1/14).

The Secretariat of the Convention of Biological Diversity (CBD) has now published “An Updated Synthesis of the Impacts of Ocean Acidification on Marine Biodiversity”. It furthers past research and work on ocean acidification and its consequences. Among other things the 2014 report provides a more detailed explanation of how ocean acidification impacts the physiology, sensory systems and behaviour of marine organisms, which undermines ecosystem health. Impacts due to ocean acidification are already happening and the future projected impacts may have drastic irreversible effects on marine ecosystems.

There are ample knowledge gaps, making it difficult to assess how future changes to ocean pH will affect marine ecosystems, food webs and ecosystems, and the goods and services they provide. Surface waters in polar seas and upwelling regions are increasingly at risk of becoming undersaturated with respect to calcium carbonate, thus dissolving shells and skeletons that are not protected by an organic layer. Acidification may interact with many other changes in the marine environment, local and global, making the consequences difficult to predict. Hence, further investigation of existing variability in organism response to ocean acidification in order to assess the potential for evolutionary adaptation is necessary, which also needs to involve a range of stressors.

The findings of the 2014 CBD synthesis are further underpinned by two new studies.

The first study: the so-called “lugworm study” by Dr Lewis, from Exeter University, suggests that the effects of acidification may be even more pervasive than earlier thought and also that the biological effects of the chemical change in the oceans are hard to predict.

Until now studies have identified species with calcium-based shells as most in danger from changing chemistry. Dr Lewis has found that other creatures will also be affected because as acidity increases it creates conditions for animals to take up more coastal pollutants such as copper. Creatures like sea urchins, unable to control their internal body chemistry, are also harmed by uptake of copper. This adds to the damage they will suffer from increasing acidity as it takes them more and more energy to calcify their shells and spines. Regarding corals, it is predicted that many of the branching and table corals, which provide shelter for tropical fisheries, are unlikely to last out the century.

Secondly, research by Andy Ridgwell and Daniela N. Schmidt in “Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release”, applies a model that compares current rates of ocean acidification with the greenhouse event at the Paleocene-Eocene boundary, about 55 million years ago, when surface ocean temperatures rose by around 5–6°C over a few thousand years. On the basis of their approach of comparing model simulations of past and future marine geochemical changes, the authors infer a future rate of surface-ocean acidification and environmental pressure on marine calcifiers, such as corals, unprecedented in the past 65 million years, and one that challenges the potential for plankton to adapt. They also argue that for organisms that live on the sea floor, rapid and extreme acidification of the deep ocean would make their situation uncertain.

Miriam Markus-Johansson

Sources:  “An updated synthesis of the impacts of ocean acidification on marine biodiversity”, CBD Technical Series No. 75, 2014
Andy Ridgwell and Daniella N. Schmidt,“Past constraints on the vulnerability of marine calcifiers to massive carbon dioxide release”, Nature Geoscience, 2014
Anna L. Campbell, Stephanie Mangan, Robert P. Ellis , and Ceri Lewis, “Ocean Acidification Increases Copper Toxicity to the Early Life History Stages of the Polychaete Arenicola marina in Artificial Seawater”, University of Exeter, Environ. Sci. Technol., 2014, 48 (16), pp 9745–9753