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.
The overall score for the offshore marine zone has declined slightly from 75 in the previous year to 74 in 2018-19 with the grade remaining ‘good’.
The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.
The overall water quality grade in 2018-19 for the offshore zone remained ‘very good’.
Water quality grades are based on water quality guideline trigger values established for the waters of the Great Barrier Reef Marine Park that, if exceeded, identify the need for management responses. The guidelines are not targets or assessments of pollutant loads entering the marine environment. The results are from remote sensed water quality indicators of offshore waters sourced from the Marine Water Quality dashboard provided through the Bureau of Meteorology.
The water clarity score of 98.2 (‘very good’) in the Offshore zone is comprised of a total suspended solids (TSS) score.
The chlorophyll a score in the Offshore zone was 100 (‘very good’).
These grades have remained consistent with those of 2014-15 onwards with very little change in the scores have occurring.
The overall coral grade in 2018-19 for the Offshore zone remained ‘moderate’ with the score decreasing from 51 to 48.
The scores for the coral cover indicator decreased from 28 in the previous year to 26 (remaining ‘poor’). The score for the juvenile coral indicator decreased 71 to 68 (remaining ‘good’), and the score for the coral change indicator decreased slightly from 53 to 51 (remaining ‘moderate’), since the previous year.
The offshore coral indicator and index scores were based upon the surveys of the Long Term Monitoring Program (LTMP) in 2018-19 and the Representative Areas Program (RAP) in 2017-18 and represented 15 separate reefs in the Wet Tropics region as specified in the methods technical report (WTW 2020).
Coral cover was the lowest scoring indicator with an overall grade of ‘poor’, and of the 15 reefs surveyed four were graded ‘very poor’, nine were graded ‘poor’ and two were graded ‘moderate’. Change in coral cover was graded ‘moderate’ whilst juvenile density was graded ‘good’ and for both indicators the grade of reefs ranged from ‘poor’ to ‘very good’.
The fish index is currently under development and will be available in future report cards.
Sweatman, H. 2018. Long‐term Reef Monitoring Program Annual summary report on coral reef condition 2017/18. Australian Institute of Marine Science. Townsville.