Full moon sparks remarkable mass coral spawning

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One of the most spectacular natural events in Western Australia, the annual mass autumn spawning of corals, is predicted to occur off parts of the coast next week, between 27 and 30 March.

Department of Environment and Conservation Marine Science Program Leader Dr Chris Simpson said the event occurred in the Dampier Archipelago, Ningaloo Marine Park and Abrolhos Islands, over the period of the lowest tidal range, seven to ten nights after the full moon.

'This fascinating event in the coral reproductive cycle looks something like a pink, underwater snow storm and it attracts many divers and photographers each year,' Dr Simpson said.

'The coral spawning occurs at night, usually on an ebbing tide, beginning about an hour after sunset and continuing for two to three hours.

'Although most corals in WA spawn in autumn, a few species also spawn during spring, contrasting with the Great Barrier Reef where most corals spawn in spring/early summer.'

Dr Simpson said water temperatures along WA's coastline over the past few months had been unusually high, causing coral stress that results in coral bleaching and mortality if it persists.

'Bleaching has been recorded on many WA coral reefs in the past month, from the tropical north to the temperate coral reefs off Shark Bay and the Abrolhos Islands where it had not been previously observed,' he said.

'The higher than usual ocean temperatures are mainly due to the La Nina weather pattern which causes the Leeuwin Current to flow strongly along WA's coast bringing warm water further south than usual.

'La Nina is often also associated with calmer weather in WA, which reduces flushing of lagoon waters causing further warming of shallow, coastal waters by the sun.

'If calm conditions occur during the coral spawning period this year it will increase the risk of coral spawn slicks forming on the ocean surface reducing oxygen and causing mortality in coral, fish and other reef biota.'

Dr Simpson said these events had occurred several times on WA coral reefs in the past and were important natural disturbances on our reefs. He said coral spawn slicks were often confused with large algal blooms.

'These blooms are usually a reddish-brown in colour, earning them the name ‘red tide', and are often confused with the pink coral spawn which also floats on the sea surface.'

DEC is calling for people who see coral slicks, distressed, floating or washed up fish or bleached corals, to take photographs and record the time, date and location of these observations and pass this information onto their local DEC office.

'Public assistance will help us to better understand where these natural disturbances are occurring, which is likely to be in vulnerable areas like shallow, protected or semi-enclosed parts of bays and lagoons.'

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