Healthy coral reefs rely on the unique abilities of the coralline algae.
Coralline Algae
These are unusual marine plants with a hard skeleton, and although they are ubiquitous, they are often overlooked. They are usually pinkish in colour, and will cover any solid substrate (rock for example) in shallow seas and on the shore.
Coralline algae are abundant on most rocky shores, and may cover the rocks in many tropical locations. Anyone who has strolled along beside the sea will have seen them, and most marine aquarium hobbyists will have them in their home – they are part of the live rock sold in the marine aquarium trade.
Coral Reefs and Coralline Algae
When a coral reef is damaged the skeletons of dead corals break up to form loose coral rubble. This would eventually be ground into coral sand if it were not for the coralline algae that cement the rubble together and provide a stable substrate for coral re-growth and an essential habitat for many marine organisms.
Carbon Dioxide and Coralline Algae
Different types of animal and plant react in different ways to acidification. Corals use aragonite, but the coralline algae use a slightly different form of calcite for their skeleton.
The magnesium calcite of these algae makes them highly susceptible to changing acidity – they would not function properly if atmospheric carbon dioxide levels reached 450 ppm (parts per million), and, assuming the rise in carbon dioxide levels continues at the current rate, that level will be reached between 2030 and 2040.
Synergistic Effects
Ocean acidification is the critical issue, but long before 450 ppm (carbon dioxide in the atmosphere) coralline algae will be under threat from a number of the other consequences of climate change.
Unfortunately different stresses do not add their effects in a simple way – the effect of two stresses together is much more than a simple addition of the effects. This phenomenon is known as synergy.
Rising sea levels, increasingly fierce storms, and rising sea temperature, can be expected to affect coralline algae (and therefore coral reefs) long before ocean acidification kicks in. Add to that the fact that millions of species of marine organisms will also be affected – and scientists have very little idea of how they all interact – and the situation becomes urgent indeed!
This article is about coralline algae and their relationship with coral reefs, but preserving the algae and the reefs is about much more. If the algae and reefs disappear there will be a ‘domino effect’ leading ultimately to a mass extinction. Life will survive, but "not as we know it!"
Main reference: ‘Output of the technical working group meeting.’ The Royal Society - 6th July 2009
See also ‘Mankind and Environmental Damage’ and ‘Coral Reef Crisis’.
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