Explaining coral bleaching in a simple way

In a just a few weeks I’ll be visiting Australia’s Great Barrier Reef on a four-day live aboard trip to the Outer Ribbon Reefs and Lizard Island. I studied tropical marine biology at university and I’m really excited about learning more about the reef from the on-board marine biologist.

Knowing that it can be hard to explain in simple terms what a coral is and what coral bleaching and ocean acidification are, I’m curious to see how the marine biologist communicates coral science to the guests and how much detail they go into.

But this is preamble to a future blog, today I want to show you a really good infographic I found that explains coral bleaching in a simple way.

Earlier this year, NOAA scientists announced that a third global coral bleaching event was on its way and last week, NOAA announced that the event is now underway with widespread bleaching in Hawaii which will soon spread to the Caribbean. Long term forecasting by the NOAA Coral Reef Watch predicts a 60% probability of bleaching due to thermal stress across the southern hemisphere between February and May in 2016. (See here for more details)

But what exactly is coral bleaching and why does it matter? NOAA defines coral bleaching as follows, “when corals are stressed by changes in conditions such as temperature, light, or nutrients, they expel the symbiotic algae living in their tissues, causing them to turn completely white.” Because this doesn’t quite explain everything, especially if you don’t know much about coral biology, NOAA has also made an infographic that I think explains coral bleaching pretty well.

coral bleaching infographic
An infographic by NOAA that explains what coral bleaching is. Credit: NOAA. View the infographic here.

The infographic splits the bleaching process into three stages using simple diagrams that show healthy coral, stressed coral and bleached coral. These diagrams illustrate how algae lives in the tissue of a coral and provides it with food in a relationship that benefits both parties. When conditions become stressful, algae leaves the coral, leaving it looking white or ‘bleached’ in appearance. In a separate column that uses a contrasting colour, the causes of bleaching are listed with a brief explanation of each one.

The only thing the infographic doesn’t fully explain is what happens after a coral becomes bleached and why it worries scientists. Without this information, people may not understand the significance of coral bleaching and the impact it has on the entire coral reef ecosystem. Overall, I think the infographic would be suitable for a range of audiences who are unfamiliar with coral biology but I think it’s missing the ‘so what?’ element.

I’m now on the lookout for an infographic that explains ocean acidification in a simple way. If you know of one, let me know!

Find more learning resources at the NOAA Coral Reef Conservation Programme website.

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