Gabe Watson was an experienced diver

An Australian court has sentenced a man to four-and-a-half years in prison over the death of his bride on their scuba-diving honeymoon on Great Barrier Reef.

Christina Watson, 26, drowned while diving with her husband, David Gabriel Watson, an experienced diver, 11 days after their wedding in 2003.

The sentence came after Watson pleaded guilty to manslaughter having previously denied murder charges.

Prosecutors said he had failed in his duty as his wife's dive buddy.

'Survival extinguished'

Prosecutor Brendan Campbell said Watson had failed to give her emergency oxygen when she needed it.

Watson allowed Christina to sink to the ocean floor without making any serious attempt to rescue her and also failed to inflate her buoyancy vest or remove weights from her belt to allow her to surface, Mr Campbell said.

"He virtually extinguished any chance of her survival," he told the court hearing, in Brisbane.

An instructor races to Tina Watson, seen lying on the sea floor

A dive instructor found novice scuba diver Christina Watson lying on the bottom of the ocean after her husband, known as Gabe, had surfaced.

In mid-2008 a coroner found it was likely Watson killed his wife by holding her underwater and turning off her air supply.

The American couple were on their honeymoon in Australia.

Watson, who has since remarried, voluntarily returned to Australia last month to face his murder charge.

Christina's father Tommy Thomas, her sister Alanda and friend Amanda Phillips travelled from their native Alabama to attend the court hearing.

Prosecutors had sought a five-year jail term for Mr Watson, with the possibility of parole after 18 months.