Glowworms- By the Light of the Full Moon

During particular times of the year, it is nearly impossible to walk the beach at night and not witness a green glow flicker in the water. This phenomenon, known as bioluminescence, occurs in many organisms, from bacteria to fish to worms. Because there is much to be learned about this interesting occurrence, such as when and why it occurs, researchers have found it to be a fascinating topic to study. Two such researchers, Dr. Gary Gaston of the University of Mississippi and Jennifer Hall from International Zoological Expeditions, have spent the past three years studying bioluminescence as well as the reproductive ecology and behavior of glowworms (Odontosyllis luminosa) at South Water Caye in southern Belize.

The term "glowworm" has generally been used loosely. Glowworms are usually defined as crawling, luminous insects that emit light either continuously or in prolonged glow rather than in brief flashes like that of the firefly. Some scientists have given the larvae of terrestrial luminescent beetles (fireflies) the name glowworm. These larvae produce bioluminescence by a chemical reaction that occurs between oxygen in the air and two chemicals found in special organs located on the underside of the insects' abdomen. Despite the glow given off by these larvae, they are not the glowworm species that the South Water Caye research focused on.

Unlike the terrestrial glowworms, the preferred habitat of the tiny bioluminescent worms found at South Water Caye is in the soft-sediment (seagrass beds) found throughout coastal areas of the Caribbean. Little is known about how this species of glowworm produces the bioluminescence, but previous research has established that bioluminescence among these glowworms is correlated to reproductive events, such as spawning, when eggs are released.

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The aforementioned researchers set out to discover more about the spawning events of these marine glowworms. They learned that like so many other marine creatures, glowworms choose to spawn in the days following a full moon. At this time, female glowworms leave the sediment and swim toward the water surface, releasing bioluminescent egg masses into the surrounding environment, resulting in a bright green glow near the water surface. This event is thought to attract males, which in turn also emit bioluminescence. When male and female glowworms meet at the water's surface, the females begin what appears to be a mating ritual, spinning in circles and releasing eggs. Males participate in this ritual by swimming around the females, releasing gametes. The entire spawning process of females usually lasts two to three minutes.

It is clear that bioluminescence between these marine glowworms is linked to lunar cycles and used as a means of attracting mates, but it also likely functions as a chemical defense against predators. One thing is certain, there is a lot that remains to be learned about these fascinating and complex creatures that glow under the moon.

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