#coral spawning

coral babies

Scientists in Australia have achieved the first-ever offseason coral spawning in the history of coral breeding and restoration sciences.

Animal Courtship & Couples in National Marine Sanctuaries

Read the full story at https://sanctuaries.noaa.gov/news/feb21/sealed-with-a-kiss.html

Just in time for Valentine’s Day, we’re highlighting some of our favorite examples of courtship, reproduction, and other fascinating animal interactions in your national marine sanctuaries!

Did you know that only male humpback whales sing? As whales begin to arrive in sanctuary waters in November and the breeding season kicks off, the males really crank up the volume. They sing to locate other whales nearby, compete with other males for females and space, and, most importantly, to attract a mate.

Some of the most fascinating examples of reproduction in the National Marine Sanctuary System come from corals and sponges. Corals can reproduce both sexually – which requires both male and female gametes – and asexually, which requires only one parent coral.

All across the National Marine Sanctuary System, wildlife devote different amounts of time and energy to finding and selecting a mate, forming relationships, and raising offspring (or not). From humpback whales that “serenade” their potential mates to corals that “let it all out,” read on to learn more about the birds and the bees under the sea!

A team of scientists from Southern Cross University have prepared large, floating pools around Moore Reef to collect millions of coral eggs and sperm for relocation to damaged parts of the Great Barrier Reef.

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.

Coral sex can take many forms. Here, little pink bundles that contain both eggs and sperm lift off in synchrony from the colonies of the hermaphrodite branching coral Acropora eurystoma. Other species keep their eggs inside their bodies for fertilization and brooding. CREDIT: T. SHLESINGER

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.

Data from 1980 to 1983 on the five studied species show consistent, synchronous patterns of mass spawning, based on regular lab exams of coral samples plus nighttime swims. But over 225 swim surveys from 2015 through 2018, Shlesinger discovered that only two of the five species still managed to spawn en masse during just a few nights. Three others didn’t synchronize tightly. In 2018, for instance, at least a few big lumps of the brain coral Platygyra lamellinaspawned just about every night from June 12 to July 18. Mini releases don’t create a thick enough soup of gametes to make fertilization likely or for there to be a lot left over after fish finish feasting on the bundles.

The moon still waxes and wanes regularly, but other spawning cues may be wavering out of sync with it. For instance, since 1982, when the earlier surveys were conducted, water in the northern part of the gulf has warmed about 0.31 degrees Celsius per decade, the researchers calculate. (Pollutants, especially hormone-disrupting ones, might also be sabotaging coral reproduction, the scientists say.)

Who's that reaching out from the coral reef of Flower Garden Banks National Marine Sanctuary? A sneaky brittle star!

Every August, the reef-building corals within the sanctuary put on one of the most abundant spawning displays in the entire Caribbean and Gulf of Mexico. Each coral species times its gamete (egg and sperm) release to ensure genetic mixing and that coral larvae can disperse over large distances. The gametes also provide a feast for small animals like this brittle star. 

(Photo: Emma Hickerson/NOAA)