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 2022-23 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 2022-23 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. Alternative data sources are to be identified for reporting offshore water quality as from the 2023-24 reporting year.

Key results

• The overall coral condition grade in 2022-23 for the Offshore zone remained ‘good’ since the previous year with the score unchanged at 61. The condition assessment is based on surveys of 9 offshore coral reefs. Offshore coral condition is assessed from the juvenile density, coral cover, and coral change indicators.
• The score for juvenile density decreased, whilst the scores for coral cover and coral change increased.
• Hard coral cover increased to its highest level since 2016-17 for the offshore zone and the grade improved from ‘poor’ to ‘moderate’.
• Impacts of coral bleaching from the 2020-21 summer accumulated heat stress event were minimal on surveyed reefs.
• The 2022-23 reef surveys recorded no potential, incipient or active crown-of-thorns starfish outbreaks in the offshore zone.
• All reefs have shown a general improvement in coral cover following impacts from heat stress and crown-of-thorns starfish between 2016 and 2018.

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