These underwater fireworks come from ‘sea fireflies’ looking for mates
In 2017, two evolutionary biologists snorkeling off the coast of Panama made a dazzling discovery.
Night fell over the shallow waters of Bocas del Toro, and James Morina professor emeritus at Cornell University, turned on his underwater flashlight to get a glimpse of the seafloor.
In response, hundreds of tiny blue lights came to life, rippling out in waves.
“We were both swearing into our snorkels in surprise,” he said Todd Oakleya professor at the University of California, Santa Barbara.
In a paper published On Wednesday, in Proceedings of the Royal Society B, the scientists detailed the courtship rituals of a new species of ‘sea firefly’ – a tiny crustacean, no bigger than a grain of sand, that stages a spectacular underwater display by sneezing up glowing mucus.
But these are not simple flashes. Like the synchronous group displays of lightning bugs on land, the sea fireflies’ light show is a carefully choreographed dance in harmony with the rhythm of the night sky.
“It’s an underwater fireworks display — the best Fourth of July you’ve ever seen,” he said Nicolai Hensleya postdoctoral fellow at Cornell who studies animal behavior and led the new study.
The creatures behind the eerie Panamanian light show are called ostracods. Dr. Hensley compares the tiny crustaceans to sesame seeds with eyeballs. Under a microscope you can make out the shrimp-like body of an ostracod, encased in a transparent shell.
A bizarre organ called the ‘upper lip’ makes many ostracods bioluminescent. The upper lip contains two chemicals that, when combined, create a bright blue burst.
“It literally looks like a handlebar mustache of glowing light right above their mouth,” said Dr. Hensley.
Ostracods around the world use their luminous snot for many purposes, such as performing courtship displays or forcing predators to spit them out (apparently the mucus tastes very bad). But Dr. Morin said the sea fireflies light display was “on steroids” the night he and Dr. Oakley observed them, and coordinated in a way that other species have not.
The team studied this mysterious population of sea fireflies, which go by the temporary name “EGD” (for “eager grassbed thunder”), and convinced them to perform encores of the light show in captivity. Now the researchers think they have pieced together the individual steps of EGD’s courtship dance.
The romance begins at nautical twilight – an interval when the sun has set, the moon has yet to rise, and the sea fireflies’ only competition for brightness is the light of the stars. Each male rises from the grass beds and then descends in a tight, corkscrew dive, sneezing between four and eight blobs of light while doing so. The result is stunning, the scientists agreed, like an array of Christmas lights or a string of glowing pearls.
EGD males are highly suggestive, the team found. The first male to produce glowing snot sets off a chain reaction while his neighbors follow suit, resulting in ripples of light. And the further away a sea firefly is from its nearest rival, the more snot beads it produces – perhaps because it has a better chance of courting females when its competitors are out of reach.
Although bioluminescence is common in the ocean, this kind of coordinated group display is impressive for a creature the size of a sesame seed, said Edith Widdera bioluminescence expert and CEO of the Ocean Research and Conservation Association, who was not involved in the study.
Dr. Widder praised Dr.’s research. Hensley because it provided “rare” insight into bioluminescent courtship, which is usually beyond the reach of scientists. She said the phenomenon is a striking example of convergent evolution, as both water and land fireflies separately evolved similar phenomena, even though the last common ancestor of the two creatures lived about 500 million years ago.
In some ways, Dr. Widder added, EGD’s light show is even more ingenious than that of their winged cousins: the firefly must give away its position when its light flashes, but the sea firefly can create distance between itself and its regurgitated light. . It’s like a glowing, coded map: the females of the species know how to “read” the display to find their snotty lovers, while predators continue to follow their tracks.
Dr. Hensley said he marveled at how this incredible dance played out, unnoticed and yet so close to civilization. In the seagrass beds of Bocas del Toro where the species was discovered, as the ostracods form their underwater constellations in the hope of finding love, you can hear the thumping bass from the discoteca just off the beach.