Lunar luster triggers mating orgies, guides travelers and even can even provoke magical transformations
One November night each year, beneath the full moon, more than 130 species of corals simultaneously spawn in Australia’s Great Barrier Reef. Some corals spew plumes of sperm, smoldering like underwater volcanoes. Others produce eggs. But most release both eggs and sperm, packed together in round, buoyant bundles as small as peppercorns and blushed in shades of pink, orange, and yellow.
At first, the parcels wait in the lips of corals. Then, in stunning unison, numerous corals lose their seeds, which hover momentarily above their parents, preserving the shape of the reef in an effervescent echo. Gradually, the bundles drift skyward.
The first time marine biologist Oren Levy witnessed this phenomenon, in 2005, he was near Heron Island, off the east coast of Australia. Fish, marine worms, and various predatory invertebrates zipped through the water, feeding on the coral confetti, which rose slowly from the reef in huge quantities. “It’s like the whole ocean wakes up,” says Levy, who now heads a marine ecology research team at Bar Ilan University in Israel. “You can watch videos, you can hear about it, but once you are actually in the midst of the biggest orgy on this planet, there’s nothing else like it.”
Corals continue to reproduce in the Great Barrier Reef today, though the sections that have escaped the ravages of climate change are rapidly shrinking. Swimming near the surface of the sea that memorable night 12 years ago, Levy encountered dense pink mats of accumulating eggs and sperm. There, drenched in moonlight, gametes from different colonies began to fuse and form free-swimming larvae, which would eventually settle on the seafloor, bud, and construct new coral citadels—a process now more vital than ever.
The moon is not the only environmental cue the corals use to achieve sexual synchrony on such a massive scale; water temperature and day length also matter. Yet the moon’s presence seems to be crucial. If the sky is too cloudy, and the moon obscured, the corals will often not spawn. Sometimes they delay until the next full moon. In the course of their studies, Levy and his colleagues revealed that not only do corals have light-sensitive neurons tuned to the dim blue wavelengths of moonlight, they also have genes that change their activity level in sync with the waxing and waning moon, regulating reproduction.
Scientists have known for centuries that the moon alters Earth’s ecosystems through gravity. As it spins around our planet, warping space-time, the moon contributes to a complex contortion of the oceans, producing twin bulges we call the tides. In turn, the daily marriage and separation of land and sea transforms the topography of numerous species’ homes and the access they have to food, shelter, and each other.
The moon also stabilizes Earth’s climate. Earth does not have perfect posture; it is tilted along its polar axis, circling the sun at an angle of about 23 degrees. The moon acts as an anchor, preventing the Earth from varying its axial tilt by more than a degree or two. Without the moon, our planet would likely wobble about like a dreidel, tilting a full 10 degrees every 10,000 years, and possibly oscillating the global climate between ice ages and hellish heat the likes of which no species has ever endured.
What is becoming increasingly clear, however, is that the moon also influences life in a more surprising and subtle way: with its light. Most organisms possess an array of genetically encoded biological clocks that coordinate internal physiology and anticipate rhythmic changes in the environment. These clocks are wound by various environmental cues known as zeitgebers (time givers), such as light and temperature.
Sunlight is the best-studied zeitgeber, but it turns out that for many aquatic creatures, moonlight is just as crucial. In the past few years, scientists have rekindled a long-neglected curiosity about the moon’s power to manipulate life, reviving studies on biology’s secret moon clocks.