It’s not just the atmosphere that is becoming hotter. Oceans are experiencing warmer temperatures and becoming increasingly acidic, due to the absorption by the world’s surface seawater of anthropogenically generated carbon dioxide.
This in turn has a major impact on marine species which depend on our temperate and tropical reefs to survive.
Recently-published research carried out with colleagues around the world shows that ocean acidification is the most important environmental stressor and biggest problem for coralline algae when assessed against all others.
Temperate and tropical reefs are dominated by “pink crusts”, the red seaweeds known as coralline algae that have calcium carbonate skeletons.
Only by reducing our emissions to keep atmospheric CO2 concentrations below 450 parts per million will these iconic coralline algal systems retain their diversity and function.
These coralline algae provide the backbone to coastal ecosystems from the tropics to the poles. They both cement together and form their own reefs in many tropical locations.
While coral reefs are widely known by the public, “coralline” reefs are also important. For example, Australia’s largest individual inshore reef, the 380 square kilometre Montgomery Reef, is actually a coralline algal reef.
Not only do coralline algae form these extensive reefs, but also they are the required settlement substrate for many invertebrate larvae, such as pāua and kina in New Zealand, and corals in the tropics. Without coralline algae, temperate and tropical reefs as we know them would not exist.
However, coralline algae are extremely susceptible to ocean acidification. Increasing carbon dioxide concentrations cause a complicated series of chemical consequences in seawater. Overall, ocean acidification makes it harder for many marine species to grow and build their skeletons of calcium carbonate.
Early studies found that ocean acidification would have dire consequences for coralline algae. However, the field of ocean-acidification science was then rocked with discussions that effects on other taxa (i.e. fish) were less than originally proposed, and that those early studies represented more dramatic effects than would actually occur in the future.
But in our latest study in Global Change Biology, we properly quantify the effects of ocean acidification across all previous studies using a meta-analysis approach for the first time, standardising the responses of all previous experiments on the topic to assess overall effects.
We found that ocean acidification has large impacts on coralline algal calcification, abundance and recruitment in the field, partially corroborating the early finds that ocean acidification would badly impact this taxa.
However, we also discovered some inconsistencies – namely that ocean acidification does not cause bleaching in coralline algae (in the way thermal stress does for corals, for example), nor consistent changes in their ability to photosynthesise.
We found that ocean acidification will have large ramifications for these important species that span all examined ocean basins, climates and across most orders and families of coralline algae.
More intense ocean acidification, predicted under higher emissions scenarios, will result in much greater chances that coralline algae will cease to provide their important ecosystem services of reef accretion/building and settlement substrate provision.
When assessed against all other environmental drivers (such as ocean warming and light), ocean acidification had larger effects more often than the other environmental variables.
Our only chance to keep these crucial species and the reefs they support is to now limit our carbon dioxide emissions globally.
World leaders have been converging on COP26 in Glasgow to discuss implementing reduced carbon dioxide emissions. Now is the time for these leaders to be courageous and not bow to the peer pressure of those seeking short-term economic gains in utilising fossil fuels.
Only by reducing our emissions to keep atmospheric CO2 concentrations below 450 parts per million will these iconic coralline algal systems retain their diversity and function.
If not, the important temperate reefs, such as the kelp forests and coralline algal beds, and tropical coral reefs will not persist as we know them in the coming decades.
Dr Christopher Cornwall is a lecturer in marine biology in the School of Biological Sciences at Te Herenga Waka–Victoria University of Wellington and winner of this year’s Prime Minister’s MacDiarmid Emerging Scientist award.
Read the original article on Newsroom.