Coral Bleaching: Why Some Coral Reefs Die

A lone fish swimming among degraded corals at the Great Barrier Reef.
Healthy corals wherein colorful algae live.
Bleached corals, which are one step away from dying alltogether.
A dead coral reef.
Map of Australia, with the Great Barrier Reef located in the Coral Sea in the northeast.

By providing food and shelter for many small marine species, corals indirectly are the guarantors for larger fish visiting coral reefs and feeding there. Thus, if corals die, it is naturally going to take a toll on both smaller species, which depend on corals, and larger fish, which depend on the smaller creatures dwelling on the reefs.

Given that larger fish, as was just implied, would decrease in number if corals died, vanishing coral reefs would have negative effects for all of the people who depend on seafood for their survival, especially the many people who fish directly on coral reefs. Furthermore, the loss of biodiversity that disappearing coral reefs entail would result in a decline in species that could potentially advance science, and quite notably, a loss of natural beauty. For these reasons, the fact that Australia’s emblematic Great Barrier Reef has begun to wither away has many people worried, with various environmental groups being determined to do what they can to thwart further degradation.

Rising sea temperatures

To be able to thwart the degradation of the Great Barrier Reef and other coral reefs, one must first understand that coral degradation is caused, among other things, by rising sea temperatures. Specifically, what warmer water does to corals is stressing the algae that live inside them. The algae, which normally provide corals with building material in the form of oxygen and sugar, as a result of the stress, slow down their photosynthetic activities. This slowdown in oxygen and sugar production, subsequently, renders the algae unproductive and rather useless for corals, causing the corals to instinctively eject the stressed but colorful algae from their bodies.

Bleached corals

What remain after algae have been ejected from corals are the corals’ white limestone skeletons, commonly referred to as bleached corals. Bleached corals are one step away from dying, and if colder water and new algae don’t soon provide new building material and thereby resuscitate the bleached corals, they will decompose.