Coral reef grows off Sydney beach as warmer waters attract tropical fish

The record-breaking warm water threatening the Great Barrier Reef is having unforeseen consequences further south.

Just off Manly's popular beaches, a sub-tropical coral species is thriving. 

The ABC reports that in the waters of Manly's Shelly Beach, just 10 kilometres from Sydney's CBD, scientists are in search of tropical fish.

Marine ecology professor David Booth says in the last few years that scientists have been looking "we've seen massive changes offshore and inshore in terms of the tropical arrivals".

Tropical fish like the sergeant major and the dusky butterfly fish are calling the harbour city home.

Initially, very few would survive the cool winter temperatures, but now they're pulling through.

"We've seen over 100 species arriving here, and probably five or six of them are the key ones so far that have managed to last until the next year," Mr Booth said.

Sydney's winter waters have increased by 1.5 degrees since 1920, and that's one reason the tropical fish can now survive so far south. 

The other is that their coral homes are spreading.

Just 50 metres from the shore, large sheets of Pocillopora coral are growing, a discovery first made in 1915.

Australia's federal government says "it remains committed to changing the outlook" for the Great Barrier Reef. The government is spending over $1 billion on various initiatives.