The great biological unknowns

While we are perfectly able to predict the decline in pH and carbonate ion concentration (CO32-), we know very little on how this is going to impact life in the ocean. How will marine calcifyers react to such a rapid and extreme change directly affecting their body structure? Which species will adapt and survive, which will die and disappear, what will be the consequences on the food web, biodiversity and fish stocks? We definitely do not know the answers, but we do know that there are many organisms and communities at risk to acidification:

• Coral reefs, already suffering from global warming, are in great danger of extinction. Due to the decrease in carbonate ions, growth of many coral reefs is expected to slow down to the point that reef erosion will be faster and their structures will start to break down. Coral reefs provide fish habitats, generate billions of dollars annually in tourism, protect shorelines from erosion and flooding, and provide the foundation for tremendous biodiversity, equivalent to that found in tropical rain forests.
• Laboratory experiments show that most calcifying organisms have difficulties growing when pH is low. This could affect commercial species such as mussels and oysters, as well as changing marine food webs and leading to substantial changes in commercial fish stocks. This in turn threatens protein supply and food security for millions of people as well as the multi-billion dollar fishing industry.
• Laboratory experiments also have shown us that many biological processes that make the environment the way we know it, can be affected by pH. Processes ranging from the cellular-level — acid-base balance, oxygen transport, cell membrane ion transport and protein function — to organism level — growth, development, reproduction and survival — to population level —  detecting habitats, signalling and communicating between individuals, detecting prey and predators — could be at risk to changing pH and any changes at any level will alter the ecosystem. 
• There are a few places in the world that have naturally high CO2 waters, such as around the island of Ischia, Italy. These sites tell us that when pH decreases to values that are expected for the end of the century, some marine species are totally absent, the biodiversity is highly reduced, and there is a complete regime shift in the ecosystem, where seagrasses and invasive species thrive but calcifying organisms do not.
• Past records of natural high-CO2 events throughout Earth’s history show a high correlation between elevated concentrations in the air and extinction of marine species.

We urgently need to learn more about the scope of these risks and predict with more certainty what will really happen if CO2 emissions continue to rise. So far, most laboratory experiments have been carried out over just hours, weeks or a few months, which means that we haven’t been able to test the potential for acclimation and adaptation by organisms. The overall goal of EPOCA is therefore to fill in these numerous gaps in our understanding of the effects and implications of ocean acidification:

• We dig back in the Earth archives, in particular through sediment cores and deep-sea corals, to find out what past natural variations in ocean chemistry can teach us for the future.
• Through a new range of laboratory and field experiments we want to determine the sensitivity of marine organisms, communities and ecosystems to ocean acidification. How species react and what are their limits of resistance: what are the “tipping points” beyond which life is giving up? We will intensify laboratory experiments focusing on key organisms selected on the basis of their ecological, biogeochemical or socio-economic importance. And we will investigate on the field, as much in situ as possible, in conditions as close to reality as possible, what is underway in the most sensitive region to ocean acidification: the Arctic.
• We will compile all our findings in ocean-climate computer models to upscale the various processes involved and be able to project future responses of the Earth system to ocean acidification, combined with the effect of climate change.
• We will assess uncertainties, risks and thresholds related to ocean acidification from the cellular to the ecosystem scale, and from local to global. We will determine where are the most critical tipping points – those thresholds beyond which the system undertakes irreversible major shifts – what scenarios of CO2 emissions are required to avoid them, and we will describe the state change and the subsequent risk to the marine environment and Earth system should these emissions be exceeded.