Ocean acidification is known to be a huge problem for organisms which make their shells and skeletons from calcium carbonate. This effect is well known for topical corals and plankton and the future of coral reefs is in our hands. 

More acidic oceans reduce the amount of carbonate in the water and can also dissolve existing calcium carbonate structures.

Deep Sea Coral Reefs At Risk From Ocean Acidification

A new study by collaboration of scientists from Scotland, Charleston, SC, and the Netherlands has highlighted how deep sea coral reefs are at great risk from ocean acidification.

Cold water corals (CWC) are typically restricted to temperatures between 4°C and 12°C (39.2°F and 53.6°F) and oceanic waters. At high latitudes this range is around 50 – 1000m depth and up to 4000m depth at low latitudes, which is below the warmer shallower water. 

These cold water coral reefs can be absolutely huge; up to 300m high and running many miles long. As they thrive in cold water they have a global distribution, which makes ocean acidification a global problem for cold water corals.

Rising Carbon Dioxide Levels – The future of coral reefs?

As rising carbon dioxide levels increase ocean acidity the very skeletons of the corals could crumble and fracture. Deep sea corals often construct their skeletons from aragonite, a calcium carbonate polymorph. There is something called the aragonite saturation horizon (ASH), which is the depth at which aragonite becomes undersaturated. Below the ASH aragonite is a lot harder to form and existing structures may start to dissolve. Reefs are delicate ecosystems, and just like the nitrogen cycle in an aquarium, they are easily thrown off balance. 

As ocean acidification progresses the ASH in most oceans will rise above the majority of CWC reefs over the coming decades. Therefore ocean acidification will have a direct impact on the structural integrity on these reefs. Potentially this impact will be very rapid. CWC reefs are formed of live corals at the edges of a huge matrix of dead coral aragonite skeletons. As the ASH rises the dead coral skeletons will be affected; these are the load bearing parts of the reef. Potentially this impact could be devastating. 

The reefs that the study focuses on are in the South California Bight. The authors studied the corals of this reef both above and below the ASH. They also took live samples from this reef and took them to the lab for further study. 

Both strategies showed that the dead coral skeletons, which form the backbone of the reef, were much more porous beneath the ASH. They also measured the most acidic pH level ever recorded on a reef. Scientists also believe that losing the coral skeletons exaggerates the destruction of surrounding coral, much like they water an aquarium filter helps 

Porosity in corals, known as coralporosis, leads to the general weakening of the reef and is detrimental to the future of coral reefs. This happens in locations key to the stability of these reefs. Experts warn that this will cause early breakage and cause the reefs to crumble, leaving them only able to house a small fraction of the biodiversity they normally do. This will cause the whole coral reef ecosystem to collapse, as the corals are the backbone to this way of life. 

The scientists leading this research found that there were parallels between coralporosis and osteoporosis in bones. This link between the two could open up an array of methods which could have uses such as monitoring and predicting the decline or survival of deep sea coral reefs. Deep sea ecosystems are notoriously fragile and the challenges faced in monitoring them are huge, so this link could be massive for the field. 

One of the authors of the study said, “By being able to adapt strategies to coral reefs that are used routinely to monitor osteoporosis and assess bone fracture risk, we may have powerful non-invasive tools at our disposal to monitor these fragile ecosystems.”

Models that can be developed from this research can drive future conservation and management efforts. They will hopefully be able to indicate which reef ecosystems will be at risk, the timeframe of this risk, and what impact it will have on biodiversity. 

Hopefully this will be able to aid conservation efforts enough to steady the ship and save the future of coral reefs!

Citation:

Sebastian J. Hennige, Uwe Wolfram, Leslie Wickes, Fiona Murray, J. Murray Roberts, Nicholas A. Kamenos, Sebastian Schofield, Alexander Groetsch, Ewa M. Spiesz, Marie-Eve Aubin-Tam, Peter J. Etnoyer. Crumbling Reefs and Cold-Water Coral Habitat Loss in a Future Ocean: Evidence of “Coralporosis” as an Indicator of Habitat Integrity. Frontiers in Marine Science, 2020; 7 DOI: 10.3389/fmars.2020.00668

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