This episode is brought to you by the Music for Scientists album, now available on all streaming services.

To start listening, check out the link in the description. [ ♬ Intro ]. Coral reefs have always been known for their beauty, but lately, they’ve ratcheted things up a notch.

Marine biologists are seeing corals that are normally drab in vibrant pinks, greens, even purples. As pretty as they are, though, these vibrant visuals are a warning that the animals are really stressed out— and if things get much worse, they might not make it at all. A coral reef is a natural condominium made by thousands of tiny animals called polyps.

But coral polyps can’t build reefs on their own. They rely on microscopic algal partners that take shelter in their tissues. The algae photosynthesize, meaning they use pigments to capture the sun’s energy to make food — some of which they eat, some of which they give to the coral.

And by absorbing high-energy light, those pigments also act as a natural sunblock. But they can’t protect the corals from heat. And heat-stressed algae abandon their coral pals.

And without the algae’s pigments, you can see right through the polyp tissue to the coral’s white, mineral skeleton — which is why this phenomenon had been dubbed coral bleaching. This bad breakup sickens the coral, and if the coral stays single for too long, it will die. Sadly, since the 1980s, corals have been bleaching regularly worldwide as ocean temperatures rise from global climate change.

But in many places, scientists are seeing something else: colorful corals, in flamboyant greens, reds, pinks, and purples. After looking closer, they figured out these colors are a way for the corals to fight back against bleaching. Essentially, they’re making their own sunblock.

See, like algae, corals can produce pigments. These pigments don’t make food, but they do protect them from light stress because they reflect some high-energy light. They also absorb some of it and then re-emit it as longer, less damaging wavelengths — essentially converting that light to a different color.~ And that’s literally why they’re so vibrant — the color we see is that converted light!

Now, corals actually produce these pigments all the time. It’s just that, usually, they’re only made in the growing edges of the coral that algae haven’t had the chance to colonize, because that’s where the animals experience the most intense light. But a 2020 study found that, when a coral bleaches, the light bouncing around in the white coral skeleton can stimulate all the coral’s tissues to produce them.

And this infusion of coral pigments gives the bleached coral a colorful hue. So ultimately, that’s why colorful corals are showing up all over the world — because they’re seriously stressed and missing their internal partners! The good news is that a coral’s pigments may help restore its relationship with algae.

In lab experiments, coral tissues that turned pink had more algae partners after about a month. That may be because the algae “sensed” the kind of light they love most: those longer wavelengths coming from the coral’s pigments! Plus, field evidence in Panama showed that bleached corals that deployed their blue or green pigments had better survival.

So, the colorful pigments that evolved to protect a coral’s growing edges before algal partners arrive seem to help them recover when those partners abandon them. That is, assuming the heat stress is temporary. If it’s too severe or sustained, the coral may die before its algal pals can return.

So, we still need to worry about worldwide coral bleaching. But, we can be grateful that corals have a colorful trick to pull through a short-term hot flash. It’s amazing how science can help us understand the beauty of the world around us.

So can music — and that’s basically what the Music for Scientists album is about. It was written and recorded by Patrick Olsen, and inspired by all the beauty and elegance in the world — from teeny microbes to the vastness of the universe. It’s also an homage to the people of science who explore this beauty and help us understand it better — because we’re all better off knowing the truths about the world, like the real reason corals get so colorful.

And, most importantly, it’s just really good music. Like, the song Aristarchus in the Rain is quite catchy! You can hear for yourself by clicking that link in the description. [ ♬ outro ].