Coral is reproducing in broad daylight
Vetea Liao stayed late. Three or four times per week, the Tahitian-born marine scientist takes off to dive in the early morning hours. He prefers to begin when the first rays of sunlight penetrate the horizon’s surface. However, that morning, November 2014, the sun was warming the waters off Moorea Tahiti’s twin island in French Polynesia when Liao could get into the water. Looking towards the bottom, Liao spotted the familiar branches of Porites rus, a common coral found on the archipelago’s western islands. It appears like a ginger root with strawberries. Liao also spotted something new which he’d not seen before. A fine fog was rising out of the coral. It appeared as if the coral was burning.
Liao was looking for his Moorea colleagues. French Centre for Island Research and Environmental Observatory (CRIOBE). This was the first time anyone had seen something like this. One person suggested the possibility that the coral was sexually active. This was a risky theory.
Coral reproduction is believed to be mostly the case at nighttime. Based on environmental signals–the complete moon or temperature variations or even the length of darkness, corals release tiny egg-like clouds and sperm in the water, which are fertilized. They then flounder with the current and settle on a new reef area. Scientists have observed corals spawning at night only once before 2014, but not before in French Polynesia. Could P. Rus Liao be watching be doing this, as well?
While he visited the lagoon numerous times, Liao didn’t see the coral haze again. In 2018, a friend noticed misty water from her deck that overlooks another lake in Tahiti. Like Liao’s first encounter, it was just two hours after dawn. With the confirmation of the timing to go looking, Liao soon got proof that the haze had been what his friend had suspected as a sure indication of coral spawning in the daylight. In the following two years, the researcher and twelve others also recorded morning spawning events on Tahiti, Moorea, and four other islands of the archipelago. P. the rus sex, as he discovered, occurs similarly to clockwork, five days after the moon is full, from October until April, approximately two hours after sunrise, roughly 7:15 am within French Polynesia. On deeper reefs, P. Rus is the one to do the dirty work after 10:00 am.
Liao currently has a team comprising more than 100 locals – families, schoolchildren, fishers, and divers who have reported 226 spawning events with P. rus who have surveyed over 100 coral reefs across 14 islands, including several remote atolls. “Without citizens, it would have taken ages to know all this,” Liao states.
In the year 2020, the marine biologist Camille Leonard witnessed the precision of spawning in the morning at CRIOBE in the area where she was observing P. rus coral growth in tanks while divers were examining an adjacent reef. “The Porites spawned at the exact same minute [in the two places],” Leonard claims. Liao’s timing was perfect. “Okay, he knows what he’s doing,” Leonard says. Leonard.
This remarkable synchrony goes far beyond Polynesia. In December 2022, after studying Liao’s work via Facebook, Coral scientists Victor Bonito with Reef Explorer Fiji P. rus recorded coral spawning at sunrise for two hours in Fiji, over three thousand kilometers away. Similar to Reunion Island. Reunion is located 15,000 kilometers further away, in the Indian Ocean. However, reports of spawning during the day are generally highly uncommon. Liao isn’t published yet with his findings, which he conducts via the non-profit organization Tama No Te Tairoto (Children of the Lagoon in Tahitian) in addition to his job as a full-time researcher and developer of sustainable pearl farming methods for France’s Department of Marine Resources. According to him, the publishing process is second to sharing his knowledge with locals who have assisted in the survey of the reefs.
The team’s work is remarkable. “I have not heard of such an extensive citizen science project for coral spawning before,” says James Guest, a coral researcher at Newcastle University in England who established the Coral Spawning Database. Her contributions to this database, which collects and makes available data on coral spawning time in the Indo-Pacific, fill in the gaps in science regarding the Porites corals. “In the Indo-Pacific particularly,” Guest states, “there’s so much focus on Acropora [corals].”
Also impressive is that this breakthrough is already used to benefit the coral’s good. Through Liao’s research, two of the largest companies for environmental consulting within French Polynesia now recommend that developers stop their work near the coast during the P. Rus spawning time to ensure that reproduction is not disturbed.
The climate is shifting as it continues to change; according to Guest, corals belonging to the Porites Genus could become dominant in reefs throughout the Indo-Pacific. Porite corals are vital, he claims. They can withstand situations that can be challenging for other corals, like extreme heat, ocean acidification, and murky water. They also have a higher frequency of spawning. “It’s fair to say they are a bit more resistant,” Guest adds. However, “if [their reproduction] is disrupted, reef recovery could be slower or nonexistent,” Guest adds.
What is the trigger for the specific timing for spawning of P. rus, however, remains to be determined. It could be an exact quantity of sunlight, a particular rise in temperature, or something else. But Liao still needs to be done investigating. With the funds from Tama Taroto’s funds, he has recently put up lights on the reefs to determine if spawning could be linked to a particular frequency of light. “Maybe it will remain a mystery,” he admits. If Liao can pinpoint the cause, corals all over the globe continue to reproduce at the right time and in the light of day.