Ocean temperatures around Australia were below 2022 record values. The condition of the Great Barrier Reef remained stable.

Ocean surface temperatures were above average everywhere around Australia but below the record  temperatures observed the previous year. Mean sea surface temperature was 0.54 °C above 1961–1990 average, lower than the previous year and 0.09 °C above the 2000–2022 average. The increase in temperature is in line with clearly rising ocean temperatures since around 1970.
Australian region average sea surface temperature expressed as the difference from 1961-1990 average values (BoM / NOAA)
The Great Barrier Reef (GBR) did not experience a mass bleaching event in 2023. Marine surveys of hard coral cover, an indicator of overall reef health, are undertaken each year ending June. Data for 2022/23 showed that the recovery of hard corals after a bleaching event in early 2022 stabilised in 2022/2023. Relatively few crown-of-thorns starfish outbreaks were recorded.
An El Niño developed in the second half of 2023, and sea temperatures increased towards the end of the year. In December, Tropical Cyclone Jasper caused potentially damaging wind speeds and high river flows. The impacts of these changes on the reef are not yet known.
Hard coral cover across the Great Barrier Reef (AIMS)