​​​​​​​Ocean acidification  (OA) has become the most-studied single topic in marine science in recent times.  In October 2014, a new report, "An Updated Synthesis of the Impacts of Ocean Acidification on Marine Biodiversity," was released by the UN Convention on Biological Diversity describing the threat to marine species and ecosystems, such as coral reefs, and how the increase of acidity in the world's oceans is expected by the end of the century to cost the global economy $1 trillion dollars.​

Startling economic headlines are a reliable method of gaining increased attention for an invisible process. However, the report states that, "The increased international attention given to ocean acidification, by the CBD and other bodies, has catalysed research and helped identify knowledge gaps" (UNCBD 2014).

The Joint ICES/OSPAR Study Group on Ocean Acidification (SGOA), co-chaired by Evin McGovern (Ireland) and Mark Benfield (USA), formed in 2012 to develop an ocean acidification monitoring programme for the waters of the OSPAR area.

Bringing together experts from the disciplines of chemistry, biology, and others, SGOA addressed the challenge of designing a long-term monitoring programme that examines both the biogeochemical changes associated with ocean acidification and the responses of potentially-sensitive marine life.

The group has now drawn up an overarching monitoring strategy as well as OA chemical monitoring guidelines for OSPAR.  "We [SGOA] tried to make sure that our suggestions not only fit the OSPAR approach to monitoring but that it is also in line with what happens at the global scale because of course it is a global issue", states McGovern. Collaboration with the Global Ocean Acidification Observing Network (GOA-ON) and the Arctic Monitoring and Assessment Programme (AMAP) took place to ensure this global standard.

"We just don't have the tools right now."

There are challenges associated with OA monitoring.  OA has similarities to climate change in relation to the global scale of the problem and the inexorability of the change as well as the complex set of responses and feedback anticipated. As Benfield stresses, "OA is not your usual ailment, it is a direct consequence of increased carbon dioxide in the oceans. You can't go out and say the concentration of carbon dioxide is too high or that the pH is too low; it's a change in the conditions but it is difficult to predict how potentially-sensitive marine life will respond."

Certain areas are more vulnerable to OA, and in the OSPAR region, Arctic waters are predicted to undergo a more rapid decline in pH. There are also certain habitats, such as areas of deep-sea corals, which the group have focused on making projections for.

There are also biological challenges. Guidelines can be established for monitoring the chemistry but at present, appropriate indicator organisms aren't known. Some broad groups of calcifying organisms that are likely to show sensitivity to ocean acidification can be recommended. Benfield adds, "Based on research, pteropods and forams (Foraminifera) have shown responses but there is no cosmopolitan indicator animal in the ocean, or throughout the OSPAR area, that we can point to and say, this is what you need to collect. And when you've collected it, this is what you need to measure as an index of ocean acidification or an impact of ocean acidification.

If you look at pteropods for example, a swimming planktonic snail with an aragonite shell, that are susceptible to OA, once you get the shell, what do you measure? How do you determine if the shell is thinner or thicker or lighter or heavier? There is no index.

Deep-water corals are similar. What should be measured in these coral colonies? Individual polyps have a lot of morphological variability. What do you measure to have a hard matrix of numbers that you can sensitively and accurately detect changes with time? "

This information is not yet available, and the SGOA chairs say,  "All we can suggest is that you collect representative animals from key groups and store them appropriately and then at such time that these indices are developed, you can go back to your specimen archive and start coming up with those numbers to assess the impact."

Fluctuation

In terms of the phenology of organisms, pH levels can fluctuate. McGovern points out that the spatial and temporal variation of pH on a range of scales is important to understand, as well as the long-term trend and this is something that the monitoring strategy highlights. One case discussed during the meeting was from the western coast of the US. Upwelling events there carry more acidic water up from the depths and into coastal oyster farm areas leading to mass mortality of larvae. Forecasting and advance warnings of when these events might occur will help farmers.

McGovern explains, "They can then change the timing of water intake into their oyster hatcheries so they're not taking it in at the maximum of lowest pH."

OSPAR monitoring

With the tools and the framework provided by SGOA, OSPAR should be able to move forward with their monitoring. SGOA has presented technical guidelines for the carbonate monitoring, as well as set up protocols for data handling at ICES, which also maps how to expand to the global data requirements, in the move towards greater data exchange with global databases.

Mc Govern adds, "One of the suggestions with our monitoring approach is that by adding the chemistry, where you've got time-series, or where you're developing monitoring, for example under the MSFD or for more general biodiversity or pelagic foodweb indicators, you add value in the long term. It is just a pragmatic approach to beginning monitoring for ocean acidification."

OSPAR now has the tools and they can take the monitoring forward a little. "But it's going to be a long term game because we are dealing with a slow but progressive issue. As such, monitoring strategies need to be responsive to the rapidly evolving understanding of OA and its potential impacts and to the development of new monitoring technologies".

There are theme sessions on ocean acidification at the Third International Symposium on the Effects of Climate Change on the World's Oceans, 23—27 March in Santos, Brazil and at ICES Annual Science Conference 21—25 September in Copenhagen, Denmark.

The final report of the joint ICES/OSPAR Study Group on Ocean Acidification (SGOA) is now available in the ICES library.​​​