Bad timing for coral sex might be an underappreciated threat of climate change.
Spawning is out of sync for at least three widespread coral species in the Red Sea, says Tom Shlesinger, a marine biologist at Tel Aviv University. And warmer seawater temperatures could be playing a role.
Records from the 1980s suggest that whole swaths of corals from particular species typically let colorful egg-sperm bundles float out of their tiny mouths and up into the water on the same few nights a year, Shlesinger says. Released in a big synchronized cloud, the sex cells separate from one another, gaining a chance at fertilization during the brief time that they survive on their own in seawater. It’s “a wonder of nature,” he says.
But after four years of recent monitoring, Shlesinger argues that three of the five species studied no longer tightly synchronize their species-wide gamete releases. And few if any new colonies of these kinds of corals are showing up in recent surveys, so the species might dwindle away in the region, Shlesinger and Yossi Loya, also at Tel Aviv University, warn in the Sept. 6 Science.
Shlesinger didn’t set out to compare local spawning synchrony. But “it’s something that kind of grabbed me,” he says. After realizing some corals weren’t spawning when expected, “I started going to the sea at night.”
By the second year of his questing, he was snorkeling or diving several hours a night during spawning months. Some 150 species of corals mingle in the long, narrow gulf of the Red Sea that stretches northeast past Eilat in Israel and Aqaba in Jordan. Unlike the Great Barrier Reef in Australia, where more than 100 coral species can release their gametes together on the same night, the Red Sea’s corals spawn one species or a few at a time on their own special nights.
Shlesinger had seen corals spawn elsewhere, but the night he finally got the timing right to catch an event in the Red Sea was “magical,” he says. He first spotted small, red egg-sperm bundles drifting up from a single coral. Soon he was swimming through “a colorful snowstorm” of little red capsules rising from hundreds or even thousands of corals.
A whole species can synchronize its spawning to the same half-hour. That precision depends on an interlocking set of environmental cues. Water temperature, sunlight and wind affect the month of the event, researchers have found. The phase of the moon matters in determining the night, and local sunset cues the time.
