Corals come in a variety of shapes, sizes, and colors and build vast coral reefs that serve as shelters for vast amounts of biodiversity in the ocean. However, they are not known for being fast.
This is because, of the more than 6,000 species of coral known to science, most are gregarious, or individual animals that make homes next to each other and on top of each other. And as adults, these corals become motionless.
However, there is another type of coral that is less well known and less studied that is completely solitary. And some of these animals, known as mushroom corals, can even walk.
“They're very small,” says Brett Lewis, a marine ecologist and microscopist at the Queensland University of Technology in Australia. “And they're adorable.”
Dr. Lewis recently subjected a 1-inch-long mushroom coral to experiments using a time-lapse camera and an aquarium cut off from all other light.
On one side of the aquarium there were slivers of white light, similar to those seen in shallow coastal habitats. The other emitted a small beam of blue light, similar to the kind seen slightly deeper in the ocean. In each of the three tests, the mushroom corals showed a strong preference for blue light and were inching towards it, Lewis reported Wednesday in the journal PLoS One.
As for how mushroom corals actually move, Dr. Lewis' research has revealed that their mechanism is strikingly similar to how one of coral's closest relatives, jellyfish, moves.
“Jellyfish are able to move through the water by twisting and contracting the muscles inside and around their edges in time with the bell-shaped pulsations,” he says.
Dr Lewis said mushroom corals have a body shape similar to a jellyfish bell and spend a long time inflating the outermost tissues of their bodies before quickly releasing them. “This allows the coral to jump across the substrate in a sort of forward-jumping manner,” he says.
To be clear, mushroom corals can move, but it takes a long time. In the time-lapse video, the coral appears to be quite active. But in real time, it can take hours for a mushroom coral to move just a few inches. In the study, a series of “periodic pulses” moved the mushroom corals 220 millimeters over a period of one to two hours.
“I looked at this for a long time, wondering if it was going to explode,” Dr. Lewis laughed. “I thought, 'Christ Almighty, it's going to take a long time for this to happen.'”
The idea that corals migrate was first proposed in 1992 and first documented in 1995, but the scientists who first described their behavior did not have the highest resolution videography at their disposal. did. This meant that scientists could not fully explore the biomechanics required for corals to swim. But now Dr. Lewis and his team have shed light on this little-known corner of marine biology.
The study “provided more detailed information about the movement mechanisms and behavior,” said Bart Hoeksema, a coral taxonomist at the University of Groningen in the Netherlands who was not involved in the new study.
There are many reasons why mushroom corals want to migrate. This animal often begins its life among colonial corals. However, these habitats tend to be crowded and exposed to waves. Mushroom corals are then obliged to migrate to deeper, calmer waters, where they colonize sandy bottoms along with other conspecific corals. This also helps animals reproduce.
Migration “could help them escape adverse situations, such as being buried under a layer of sand, falling over, or getting too close to aggressive space-seeking competitors, such as toxic sponges.” Dr. Hoksema said.
The gradual movements of mushroom corals may seem insignificant when compared to the distances traveled by other migrating creatures such as wildebeest, monarch butterflies, and arctic terns. But such creeping movements have been beneficial to this species for hundreds of millions of years.
“On their scale, they are very small, so this is a very large movement for them,” Dr. Lewis said. “They have a very simple system that moves the length of their body in a very short amount of time. It's a sprint for them.”
