The northern boundary of the Central inshore reporting zone area extends north-east from Cape Grafton just south of Cairns to the offshore boundary and includes enclosed coastal, open coastal and mid-shelf waters.
The southern boundary of the Central zone extends due eastward from the mainland just south of the Moresby River at Double Point to the boundary of the offshore waters.
The major rivers discharging into the central zone are the Mulgrave River the Russell River and Johnstone River. The Moresby River discharges into the southern coastal area of the Central zone. Numerous smaller waterways drain coastal sub catchments that discharge into the Central zone.
Water quality in the Central zone is affected by plumes of sediments, nutrients and pesticides from rivers discharging directly into the zone but also from the plumes of southern rivers, particularly the Tully/Murray, which are carried north by prevailing currents.
The area includes Fitzroy Island to the north, the High Island Group some 12km north-east of Deeral, the Frankland Island group approximately 16 km due east of Deeral and Normanby Island located between the High Island group and the Frankland Island group. These islands provide fringing shallow water environments that support coral reef ecosystems.
The overall grade for the Central zone remained ‘moderate’ with the score increasing slightly from 57 in 2017-18 to 59.
The diagram below shows the detailed results for each indicator by year. Click on the timeslider to see data from previous years.
The water quality grade in 2018-19 for the Central inshore zone was ‘moderate’ and scored 58.
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 derived from in-situ water samples taken at ten locations and from water quality loggers at four locations from inshore waters extending from sites at Fitzroy Island in the north to sites at the Frankland Island Group in the south. In addition, passive pesticide samplers are located at High Island.
The water clarity score of 70 (‘good’) increased from 41 (‘moderate’) in 2017-18. Water clarity is comprised of total suspended solids (‘good’) and turbidity (‘good’).
Nutrients scored 21 (‘poor’) and decreased from 53 (‘moderate’) in 2017-18. Nutrients are comprised of oxidised nitrogen (NOx), particulate nitrogen (PN), both graded ‘very poor’ and particulate phosphorus (PP) graded ‘poor’. NOx, PN and PP concentrations were highest at sites closest to the mouth of the Russell-Mulgrave . Concentrations of all three nutrient indicators were highest during and following high river discharges between December and February.
The chlorophyll a score in the Central zone was 51 (‘moderate’).
Using the pesticide risk metric pesticides were graded ‘very good’ and scored 89, equating to greater than 99 percent of species protected.
The overall coral grade in 2018-19 for the Central inshore zone was 60 (‘moderate’) and decreased from a ‘good’ grade in 2017-18.
The coral grade is comprised of the density of juvenile hard corals score of 41 (‘moderate’), the macroalgae cover score of 64 (‘good’), the coral cover score of 66 (‘good’), the change in coral cover score of 73 (‘good’), and the coral community composition score of 58 (‘moderate’).
The decline of coral condition in the Central zone to ‘moderate’ was due to the lowering of the index score by one since it was on the threshold of ‘good’ in 2017-18. The indicator that declined the most was macroalgae cover, whilst low scores for macroalgae cover and juvenile coral density continued at Franklands West sites.
Further information about recent changes in the coral index for the central zone are available from the latest Marine Monitoring Program inshore coral report (Thompson et al. 2020).
There is currently no seagrass monitoring undertaken in the Central zone and consequently no seagrass grade can be calculated for this zone.
The fish index is currently under development and will be available in future report cards.