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BIO BITS - Coral Spawning

Coral Spawning Courtesy of Shane 'Sharkey' Down

The annual phenomenon known as coral spawning was observed at Low Isles (inshore reefs) on the night of November 6. Quicksilver’s Head of Reef Biosearch Russell Hore said there remains a possibility of a mass spawning at the Outer Reefs in early December.

Mother Nature’s way of maintaining a consistently robust gene pool, coral spawning was unknown to science until 1982, when several marine biologists working on the Great Barrier Reef observed it in the wild for the first time.

Corals have two reproductive methods: asexual and sexual. The asexual process is where the individual polyps split and divide to increase overall size of the colony, and this process occurs continuously throughout the year. However, to maintain a consistently robust gene pool, corals need to have a sexual phase to exchange genes – this is known as coral spawning.

The time of the mass spawning varies from area to area, but at the Great Barrier Reef, it occurs in November to December.

There are a number of environmental cues that the corals rely upon to stimulate them to spawn. Foremost is temperature, requiring an ocean temperature of 26oC or above for the month before for the eggs and sperm to mature. Secondly, they will generally reproduce 4 to 6 nights after the full moon in November or December, when the tides are “neap” (where there is little tidal movement). As opposed to a lot of fish species that take advantage of large outgoing tides to sweep their eggs into the relative safety of open water, corals prefer little water movement so that the fertilized eggs can settle on suitable substrate. Thirdly, it will generally be about 2-3 hours after the sun sets, because it’s nice and romantic, and more importantly most of the plankton feeders will be asleep, giving the eggs more time to settle to the relative safety of the reef.

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Coral spawning was witnessed at Great Adventures' Norman Reef platform on the outer Great Barrier Reef on Monday 7 December!

Photo Courtesy of Shane 'Sharkey' Down