July 16, 2017 Biodiversity Written by Megan Ray Nichols
deep-water corals
When most people think of corals,

they picture the brightly colored structures that live near the surface of the water. But there’s another type of coral that lives in slightly deeper and colder waters as well. This sea creature has a pretty incredible way of surviving its deep-water condition.

What are deep-water corals?

The majority of the coral species we know about live at depths of about 50 to 60 meters below the water’s surface at temperatures as low as 30 degrees Fahrenheit — deeper and colder than the conditions other coral need to survive.

Although these deep-water corals are plentiful, we don’t know much about them, because they’re more difficult to reach. They’re also extremely fragile, which makes them harder to study. Until recently, few scientists displayed the motivation to really research them.

Like tropical corals, deep-water varieties house a wide range of marine life. Unlike tropical corals, though, deep-water corals give off a yellow, orange or red glow. Until the completion of recent research, we didn’t know much about how they survive and why they glow so brightly. As it turns out, the two things are related.

How tropical corals survive

We know more about tropical corals due to their location near the surface, which makes them easier to access. They live in shallow waters with temperatures of about 68 to 90 degrees Fahrenheit.

Tropical corrals live near the surface because they require sunlight to survive. In addition to the many other marine creatures corals play home too, they also host algae called zooxanthellae. Corals depend on these algae, which live inside of them, to survive. The algae perform photosynthesis for the corals, providing them with nutrients and the colors for which they’re famous.

In order to protect their algae from harmful ultraviolet rays, the corals deploy a type of fluorescent protein that acts as a kind of sunscreen for the algae. It absorbs the ultraviolet light and reflects back green light. This gives tropical coral a distinctive green glow, just like deep-water corals’ red, orange or yellow glow.

How deep-water corals survive

Corals that live in deeper water, though, don’t get as much as sunlight because it’s hard for the sun’s rays to penetrate that far below the surface. These corals, recent research suggests, employ a similar tactic to that of their tropical counterparts.

Deep-water corals also use a fluorescent protein, but instead of glowing green, it glows red, orange or yellow. And instead of blocking ultraviolet rays, it takes the little bit of light that reaches that far down into the water and amplifies it so it can reach more algae.

Not much sunlight is able to reach deep-water corals, and much of what does is blue light. Red hues can reach further into the corals than blue ones can, so the corals convert that blue light into shades of red, yellow and orange. This provides the algae with more light and allows them to produce more food.

What does this all mean?

This recent research has expanded scientists’ knowledge of corals that live deeper in the ocean. Some researchers have suggested shallow water corals could adopt this tactic to survive the coral bleaching episodes that have ravaged coral reefs worldwide.

If tropical corals could adapt this strategy, it might help them produce more food for themselves. However, studies indicate the two types of corals have two distinctive types of proteins and shallow water corals couldn’t easily adapt to low-light situations.

The fluorescent pigments in deep-water corals may prove useful to the medical field. Biomedical researchers use these pigments as markers in medical imaging research. Red proteins could be especially helpful, because they can emit light deeper into cells and tissue.

This new research shows the incredible ability of corals to figure out how to survive. It also shows us that tropical corals may not be able to adapt quickly enough to avoid the damage caused by bleaching events. We need to ensure conditions are suitable for corals in shallow waters if they are to survive.


This is a guest post written by Megan Ray Nichols.
nicholsheadshotMegan Ray Nichols is a science writer and the editor of Schooled By Science. She enjoys discussing scientific discoveries and exploring the world around her. Follow her on twitter @nicholsrmegan