Both female and male Bermuda fireworms (Odontosyllis enopl) luminesce during a precisely timed mating display in the fall.

© James B. Wood

The mating ritual of the Bermuda fireworms (Odontosyllis enopla) is precisely timed. Beginning on the third night after the full Moon in summer and fall, at 55 minutes after sunset, spawning females come up from the seafloor and secrete a bright bluish-green luminescence that attracts males.

“It’s like they have pocket watches,” said Mercer R. Brugler, a Museum research associate and lead author on a new study published on August 8, 2018, in the journal PLOS ONE investigating the phenomenon and the fireworms’ physiological changes during mating.

The fireworms’ bioluminescence was first documented in 1492 by Christopher Columbus and his crew, who described witnessing a mysterious lighting event that looked like “the flame of a small candle alternately raised and lowered” before making landfall in America. The stunning display went unexplained until the 1930s, when scientists identified Columbus’ description as the mating behavior of Bermuda fireworms, which are known to live throughout the Caribbean.

Sunset in Ferry Reach in Bermuda, where the fire worms were collected for the study.

© AMNH/M. Siddall

“The female worms come up from the bottom and swim quickly in tight little circles as they glow, which looks like a field of little cerulean stars across the surface of jet black water,” says Mark Siddall, a curator in the Museum’s Division of Invertebrate Zoology and author on the study. “Then the males, homing in on the light of the females, come streaking up from the bottom like comets—they luminesce, too. There’s a little explosion of light as both dump their gametes in the water. It is by far the most beautiful biological display I have ever witnessed.”

Just prior to this swarming event, the worms’ four eyes become enlarged and pigmented, and their nephridia (an organ similar to vertebrate kidneys) adjust to store and release gametes.

Siddall, Brugler, and colleagues looked at the full set of RNA molecules, known as the transcriptome, of a dozen female fireworms from Ferry Reach, Bermuda. They found that the fireworms’ seasonal light show was due to the production of a special luciferase enzyme in their genes, similar to those found in copepods, fungi, and jellyfish. But the team’s findings show the fireworms’ enzymes to be unique among bioluminescent organisms across the tree of life.

“It’s particularly exciting to find a new luciferase because if you can get things to light up under particular circumstances, that can be really useful for tagging molecules for biomedical research,” said Michael Tessler, a postdoctoral fellow in the Museum’s Sackler Institute for Comparative Genomics and co-author on the paper.

Read the full study.