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Lessons From the Mediterranean About Ocean Acidification

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Today’s guest blog comes from Jason Hall-Spencer — a Professor of Marine Biology at Plymouth University in the United Kingdom. His research spans seamount ecology, fisheries , ocean acidification, aquaculture and conservation. He’s also working on marine protected area design using satellite vessel monitoring for fisheries management. He does his fieldwork all over the world, at volcanic CO2 vents in the Mediterranean, coral reefs in the Arctic, the NE Atlantic, and off Papua New Guinea. Follow him on Twitter at @jhallspencer.

In 2006, when I first heard about ocean acidification, I started running expeditions near underwater volcanoes in the Mediterranean where CO2 bubbles up through the sea floor, acidifying large areas for centuries. We have found similar ecosystem shifts at all the seeps, so I am now convinced that ocean acidification will bring change.  In a recent article I attempt to put this topic into context, focusing on two major causes of change – the corrosive effects of CO2, and the way the extra carbon is used as a resource.

Here’s what we’ve noticed about the sea life around those natural CO2 seeps in the Mediterranean: algae seems to thrive, whereas animals with calcium carbonate shells—like plankton—dissolve away. We see a lot of brown seaweeds on the seafloor, and they often overwhelm slower-growing competitors like corals. Although life is abundant at CO2 seeps, there is far less diversity than we see elsewhere.

Reefs formed by corals or mollusks are severely weakened as CO2 levels rise, which is clearly a concern since ocean waters around the world are becoming increasingly acidified. As reefs weaken, we will see ripple effects onshore and in the water. In the tropics, weakened reefs will likely worsen coastal erosion, which is already a problem due to rising sea levels, increased storminess and the loss of protective habitats such as mangrove swamps.

Some plants and animals, typically the ones without shells, can adapt to the effects of long-term acidification. Jellyfish, anemones and soft corals do especially well, but when we transplant hard corals into areas with an average pH of 7.8, they dissolve away. So acidified oceans could end up dominated by much fewer species living among crumbling reefs and competing with soft-bodied jellyfish and seaweed.

What does all this mean for temperate coastal habitats and fisheries? I’m not sure. These highly productive waters may provide oysters, mussels and corals with enough food to cope well with these conditions, which make forming their shells more difficult.

Next year I hope to begin studying natural analogues for future ocean conditions in the north Atlantic, as this will reveal which organisms have more chance of coping. Perhaps algae will counteract acidification by absorbing CO2 – this could help those who earn their living through shellfish aquaculture, or who depend on reefs for coastal protection and tourism.

The past five years’ work shows ocean acidification is a serious issue with real financial costs, and that marine life is already being affected. This evidence is helping galvanize change as governments get serious about cutting emissions. Investing in research is absolutely worth it – ‘forewarned is forearmed.’ We now know that systems that are under less stress are more resilient  – I hope this new body of knowledge helps improve coastal management and strengthen marine regeneration efforts.

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