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The Good News You Missed About Ocean Acidification

Sean Connell taking notes at a vent that is emitting CO2 bubbles.  Note the pres

Sean Connell taking notes at a vent that is emitting CO2 bubbles. Note the presence of weed-like plants or turfs, which occur instead of the normally extensive kelp forests or urchin barrens.

By Sean Connell

Carbon may be acidifying the oceans, but the species it’s supposed to harm are fighting back.

We face an ever-growing number of stories about species pushed to extinction and ecosystem collapse, but few about species adjusting to environmental change and their ecosystems persisting. I contend that recognising how nature copes with environmental change is as important as understanding how nature fails to cope.

My research focuses on carbon emissions. Carbon released from fossil fuel combustion is absorbed by the oceans, causing them to acidify. Can nature adjust to these conditions?

Let’s first consider a local pollution event – an oil spill. After the Deepwater Horizon disaster released a vast amount of oil in the Gulf of Mexico, scientists discovered that oil-degrading bacteria played a significant role in reducing the overall environmental impact. These naturally occurring microbes were able to multiply and counter the oil because they have evolved the ability to draw carbon and energy from hydrocarbons for growth.

How does this local example of a short-lived event help us consider CO2 pollution as a long-lived event? Let’s consider the side-effect of CO2 on acidifying the ocean.

It’s well documented that acidification harms the calcified body parts of shellfish. However, this evidence is largely based on artificial laboratory experiments that don’t incorporate the complexity of the natural environment. Our research, published recently in Ecology (https://goo.gl/k1pT1q), discovered that when we grow plants in tandem with elevated CO2, the plants contained more calories for herbivores that eat them. These extra calories helped marine snails to build shells in an acidic environment that was meant to destroy them.

CO2 is often a limiting resource for many marine plants, so the energy they expend to obtain CO2 for photosynthesis can be reduced under CO2-enriched conditions. Calcifiers can thus benefit from the availability of more energy-dense food because it reduces the energetic burden of ocean acidification.

This example of survival does not fit the narrative that ocean acidification negatively impacts calcifying organisms, let alone the possibility that ocean acidification could even have positive effects in the wild. Indeed, when we have visited natural CO2 seeps we have found that calcifiers can actually flourish there.

These novel findings challenge current research about climate change, which has been preoccupied with documenting the direct, easily detectable, lab-based effects of ocean acidification rather than the more realistic suite of indirect mechanisms that allow species to proliferate under environmental change.

This benefit to herbivores is important because it might re­balance ecosystem productivity. For example, the positive effect of CO2 enrichment on plant production might be balanced by intensified productivity of herbivores consuming energy-rich food.

This stabilisation of plant production challenges the idea that CO2 enrichment will tip the balance of future marine ecosystems towards weedy plants, such as fast-growing turfs that displace slower-growing kelp forests and seagrasses. While CO2 enrichment does boost weed production, it also intensifies herbivory, which adjusts in strength to counter increasing weed production.

I’ve been surprised by how adjustable nature is. Individuals can adjust their feeding behaviour, and entire populations can adjust their reproduction. These quick behavioural responses compensate for instantaneous increases in weed production, and the long-term increase in population size compensates for persistent increases in plant productivity.

Nature is far more adjustable and adaptable than we imagine. While we recognise that humans have changed the environment faster than nature can adapt, we can also recognise the naturally inbuilt processes that nature has long used to adjust with change. Many of these processes may be managed to help nature keep pace with change.

Such positive insights are not only useful to people that manage nature, but also to society. Optimism provides more certainty in challenging times, whereas pessimism disempowers. Negative news therefore tends to re­inforce existing thought patterns, and this learned helplessness reduces pro-environmental behaviour.

Science needs to rebalance its research and messaging to not only bolster natural processes that adjust to cope with change, but also provide positive news that leads to a greater willingness to help nature.


Sean Connell is Professor of Ecology at The University of Adelaide’s School of Biological Sciences.