FEATURE ARTICLE – Understanding high CO2 worlds

The latest in our series of expert contributions explores the issue of ocean acidification and turning science and knowledge into advice.
Published: 15 December 2016
​​​​​​​​​​Silvana Birchenough, Marine Climate Change Centre, the Centre for Environment, Fisheries and Aquaculture Science (Cefas)​

​Ocean acidification (OA) and climate change are both influenced by an increasing carbon dioxide concentrations coming from the atmosphere. However, OA is different from climate change as it is not a climatic process but an alteration of seawater chemistry. The ocean is the largest natural reservoir of dissolved carbon and has an immense buffering capacity for changes in atmospheric CO2 concentrations. The rapid increase of atmospheric CO2 since the industrial revolution has caused oceans and seas to absorb increasingly greater amounts of it. This process disturbs the pre-existing chemical equilibrium of the sea, resulting in seas becoming more acidic.

OA has become one of the most studied topics in the last ten years. The emerging evidence suggests that OA will act differently across species and there may be direct and indirect effects for ecosystems. As research continues to advance, it is moving from an effort to understand single species' responses to one stressor to more detailed and applied approaches over multiple stressors (for example, mesocosm).

However, as newly acquired data is produced, some contradictory results are still being shown for certain test species. Furthermore, there are still different end-points being measured at several levels. So how can this newly acquired knowledge be translated into dedicated tools for large scale assessments? This is very important for populations, ecosystems, and reliant industries such as fisheries, aquaculture, and tourism.

One way is to use the individual experimental responses of organisms to inform understanding community level assessments. However, we still need to develop the wider tools to scale-up some of these observed changes (such as via modelling approaches on ecosystems). Of particular importance are the observed effects of OA on commercial species. Also, what will be the likely effects on economic resources and the ecosystem? These are fundamental questions for supporting fisheries and aquaculture. 

If we are to translate current OA information ​​​​into a picture of what the main effects will be, as well as potential mitigation strategies, we need to be able to underpin the science into evidence for shellfish, fisheries, and aquaculture. There is a clear need for integration on a multidisciplinary level to ensure the science moves in the right direction and helps us to adopt adaptive strategies to safeguard marine ecosystems. 

Building evidence for advice

Currently available evidence helps us to better understand the effects of OA on marine species. We also know that the carbonate chemistry of the oceans is changing, with marine species feeling the effects. Given the level of OA research and our understanding, the question is how can we translate this knowledge to industry, to facilitate preparation and adaptation to these changes? Some of this type of active partnerships have already taken place in the US, where oyster mortalities due to OA were observed. These mortalities provided the opportunity for industry, scientists, and end-users to work jointly to develop a monitoring programme to assess changes in carbonate chemistry and to study changes in oysters.

Understanding prevailing conditions

Marine ecosystems are dynamic, and studies have demonstrated that the pH across the world's oceans is decreasing at a rapid rate. There are some long-term observations, which provide information on how ocean chemistry is changing. What will these effects mean for ecosystems? What will be the influence on the ocean's buffering capacity? This knowledge is still in its infancy. As we know that the marine environment is often influenced by multiple pressures, we need to understand the effects resulting from such pressures as well as seasonal and inter-annual impacts against biological responses.

Some high-resolution monitoring datasets are starting to become available, some of which show that certain existing environmental conditions can be extremely variable. It is, therefore, important to understand the real conditions to which organisms are exposed and have potentially adapted and to what extent seasonal changes have allowed them to be tolerant to, before we can fully understand or even anticipate how they might react in the future. Our understanding of how individual species respond to OA and the mechanisms by which they may be able to do so to was identified as an emerging area of research by a recent OSPAR/ICES study group. Recommendations from this group, specifically on ways to foster better integration of existing carbonate chemistry time-series, will help to understand variability and change of European ecosystems as well as support analyses of changes in ecosystems more widely.

Answering the so what

One of the real challenges facing scientists is translating findings into advice. There is a tendency to concentrate of what level information is lacking rather than using that which is available for decisions or advice. Some current OA findings have been placed into social and economic considerations. These socio-economics aspects have a real meaning for end-users and can help to understand the likely effects and magnitude of expected consequences in terms of resource management, job security, future opportunities, and food security. Yet, the current level of understanding here is still very much under development. The need to continue to provide further knowledge to understand these effects is generating much attention both from policy-makers and in the media. There is though a clear​ need to further understand OA repercussions for societies and end-users and the complexity of biological and ecosystem responses.

​An active research community

Initial discussions on OA efforts took place during a workshop at the Royal Society, UK in 2005. Since then, the scientific community has taken the initiative, with publications provided further details over the last five years. 

Some of this newly acquired science may help to fine-tune uncertainties regarding the effects of OA on organisms but particularly, and more importantly, to provide further information for understanding the wider effects on ecosystems. Such understanding is needed to advance our current knowledge on the effects on commercial species and what adaptions must be considered to safeguard these stocks. There is much to consider when distilling OA priorities, and much effort is still needed in many areas. Clear questions on the factors responsible for pH variability in species and ecosystem sensitivity is pressing. There is also a need to focus on the biological consequences resulting from OA effects with other stressors and assess ​the overall repercussion for ecosystems (including fisheries and aquaculture) and end-users. 

Ongoing efforts

Despite a growing understanding of individual responses to OA, there is still a need for an overarching umbrella project or activity that could synthesise all available responses and attempted to re-evaluate the consequences of OA effects or likely changes for specific species, habitats, and ecosystems. National initiatives have developed targeted/country- specific research (such as UKOA, the UK Defra-funded "Placing Ocean Acidification into a Wider Fisheries context" (PLACID-MF1113), and BIOACID). These projects have generated useful scientific insights, but the question could be asked: what happens when these larger projects come to an end? What are the best alternatives and how do we advance the science? The issue continues to be unattended, unless there are clear impacts being observed with clear knock-on effects for the industry, food security, and job losses, ​such as the oyster hatcheries and further effects observed in the US​.

The Global Ocean Acidification Observing Network-(GOA-ON) is one network aiming to integrate science and translate it to inform governments. This initiative aims to improve understanding of global OA conditions and ecosystem responses as well as acquire and exchange the data and knowledge necessary to optimize OA modelling. Furthermore, a GOA-ON report summarizes 'requirements and governance' helping to promote ways to integrate national and international initiatives for fostering collaboration. The network has over 100 scientists.

This year has been particularly a busy year for OA research. As well as the 'Life in the High CO2 World' symposium in Tasmania, there was a PICES/ICES session "New stage of Ocean Acidification Studies: Responses of Oceanic Ecosystems including fisheries resources" held in November in San Diego as part of PICES' 25-year celebrations. 

In December, ICES/PICES Workshop on understanding the impacts and consequences of ocean acidification for commercial species and end-users (WKACIDUSE) was held in Copenhagen. It hosted scientists and industry representatives to synthesize the available science to support the advisory process, helping to translate existing information on OA effects on commercial species for decision-making in the use of marine resources.

Important science in the area of OA will continue into 2017. After the WKACIDUSE report is published by mid-March, the issue of marine carbon export and sequestration will form part of​ Theme Session I at the 2017 Annual Science Conference​. ​

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​Photo: S​ilvana Birchenough

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FEATURE ARTICLE – Understanding high CO2 worlds

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