Large Porites brain coral recorded spawning at Norman Reef, about midday on Monday during heat wave by Down Under Cruise and Dive. Photo: Down Under Cruise and Dive/GBRMPA
Large Porites brain coral recorded spawning at Norman Reef, about midday on Monday during heat wave by Down Under Cruise and Dive. Photo: Down Under Cruise and Dive/GBRMPA

Great Barrier Reef’s wild display starts early

THE Great Barrier Reef's big sex show has undergone a premature release, with Cairns experiencing a rare daytime coral spawning.

While a majority of corals on the natural wonder were expected last night to start to release their eggs and sperm into the water en masse, the annual biological phenomenon was triggered about midday on Monday at Norman Reef, about 60km northeast of Cairns.

Large brain coral recorded spawning at Norman Reef, about midday on Monday during heat wave by Down Under Cruise and Dive. Photo: Down Under Cruise and Dive/GBRMPA
Large brain coral recorded spawning at Norman Reef, about midday on Monday during heat wave by Down Under Cruise and Dive. Photo: Down Under Cruise and Dive/GBRMPA

Downunder Dive and Cruise reported to the Great Barrier Reef Marine Park Authority that its divers observed a large brain coral spawning in 5m of water for at least 45 minutes at the location at the height of Cairns' heatwave.

Divers Den operations manager Tobi Schnell said passengers on board one of the tour company's liveaboard boats also observed spawning during a dawn dive at nearby Saxon Reef.

"We're running boats the next three nights, so expecting a pretty good spawning this year," he said.

GBRMPA has reported above-average sea surface temperatures for the Reef - but not by as much as temperatures over the land, which peaked at more than 40C yesterday.

Reef Teach marine biologist Gareth Phillips, however, did not believe the daytime coral spawning had been influenced by Cairns' record-breaking extreme heat.

"Daytime spawning is still quite special, but it's not unheard of, and it's certainly not a sign that the Great Barrier Reef is all out of whack," he said. "Just like some humans, I guess some men can't hold it as long as other men.

"Some people mature earlier, and some later.

"Some corals are exactly the same."

GBRMPA chief scientist David Wachenfeld confirmed the daytime spawning was unusual.

He said mass spawning on the Reef traditionally occurred after a full moon, and only after rising water temperatures had stimulated the maturation of reproductive cells within adult corals.

"The day length, tide height and salinity levels also appear to be factors in deciding when the event will happen," he said. "Sudden changes in temperature or any other changes in the natural process appears to influence coral spawning."



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