Offshore

The single Offshore zone includes all offshore waters within the Wet Tropics NRM marine region. It extends east from the boundary of the mid-shelf water to the boundary of the Great Barrier Reef Marine Park, and is bordered north and south by the Wet Tropics NRM marine region.

Water quality in the Offshore zone is less affected by plumes of sediments, nutrients and pesticides from river discharge than the inshore zones due to its distance from the land. The boundary is typically a minimum of 20 km from the mainland. The closest point to the Offshore zone boundary is Cape Kimberley, just north of the Daintree estuary (approx. 14 km from the mainland).

The Offshore zone includes numerous coral reefs, 15 of which are included in the offshore coral surveys for the Report Card. Unlike the inshore zone where coral reefs often occur in the shallow fringing waters of continental islands, the coral reefs in the Offshore zone predominantly grow on limestone platforms that are relics of past phases of reef growth. These coral reefs provide habitats for an immense diversity of organisms including hard and soft coral species, ascidians, bryozoans, molluscs, fish, turtles and marine mammals.

For 2023-24 an overall score and grade for the offshore marine zone was not available due to insufficient data. To produce an overall grade and score at least two of the three indices are required.
For 2023-24 there was no water quality monitoring program in place to allow for reporting on offshore water quality. For previous years offshore water quality results were obtained from the BoM Marine Water Quality (MWQ) dashboard which was decommissioned in 2021.

It is intended that a marine fish index will be developed in the future to contribute towards the assessment of waterway health for the Offshore zone.

Key results

• Offshore coral monitoring for 2023-24 was conducted before Tropical Cyclone Jasper and the severe marine heat wave which occurred over the summer.

• The offshore coral index remained ‘good’ and increased from 61 to 65 since the previous year.

• Coral cover remained ‘moderate’ although the majority of reefs had an increase in coral cover.

• Juvenile density indicator remained ‘very good’ and the score increased from 84 to 92.
  Coral change remained ‘moderate’ and the scores increased at six reefs and decreased at three reefs.

• There were no Potential, Established or Severe Outbreaks of crown-of-thorns starfish recorded on offshore reefs.

• Low levels of hard coral bleaching were recorded at several reefs before the severe marine heat wave whilst medium to high levels of bleaching were recorded at all reefs from aerial surveys following the severe marine heat wave.

The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.