Marine
zones
KEY FINDINGS FROM OUR 2024 REPORT CARD
The Townsville Dry Tropics Waterways Report Card brings together monitoring data for Cleveland Bay, Halifax Bay, and the Offshore Zone beyond Magnetic and Palm Islands.
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The 2024 Report shows Cleveland Bay water quality has declined from ‘very good’ to ‘good’.
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In the 2022-2023 reporting year, Cleveland Bay water showed decline in physical-chemical properties, a measurement that considers turbidity, total suspended solids, and ‘Secchi depth’ — another technique used to assess water clarity.
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​Waters of the Magnetic Island Sub-Zone on the other hand, received a ‘very good’ grade for physical-chemical properties.
Conversely, where nutrient levels are concerned, Cleveland Bay receives a ‘very good’ overall, but the Magnetic Island Sub-Zone receives a ‘very poor’ for nutrients.
Reasons for these results may be many. Considerations include that the Magnetic Island Sub-Zone is subject to stringent Water Quality Objectives in line with its World Heritage Area values. Additionally, its proximity to the infrastructure of Magnetic Island’s residential areas is a factor. These results have been consistent for the last five years, with further investigation required to identify possible causes for these specific grades.
For concentrations of Chlorophyll a, Cleveland Bay receives a grade of ‘very good’, as does the Magnetic Island Sub-Zone. Chlorophyll a is used by microscopic organisms that conduct photosynthesis and form the base of the marine food web, providing essential energy and nutrients to higher levels of life.
While it is fundamental to support the food web, excess availability of Chlorophyll a can increase the proliferation of microscopic organisms in the water column. This then can contribute to turbidity and lower light availability, negatively affecting coral and seagrass.
For habitat, Cleveland Bay receives a ‘poor’ grade
Habitat grades for Cleveland Bay are calculated using cover, composition, and health data of seagrass and coral in Cleveland Bay.
The 2024 Townsville Waterways Report Card shows seagrass in Cleveland Bay has declined slightly against the previous reporting year, but its area of coverage has increased for several meadows across the Bay.
Coral in Cleveland Bay has fluctuated over the last four years, receiving a ‘poor’ grade in the most recent Report Card.
Macroalgae is settling into Cleveland and Halifax Bays — potentially taking up valuable real estate for young corals.
Significantly, 5 of 7 coral monitoring sites in Cleveland and Halifax Bays show a concerning amount of macroalgae (seaweed), resulting in ‘very poor’ grades recorded at Geoffrey Bay, Pandora South, Havannah South, Pandora North, and Havannah North.
The presence of macroalgae as a dominant component of a reef ecosystem indicates a disturbance or imbalance in the system, often associated with excess nutrients and coral decline.
Juvenile coral in the Offshore Zone continues to recover
All coral reefs in the Offshore Zone receive habitat grades of ‘good’ or ‘moderate’ in this year’s Report Card, with juvenile coral density graded ‘very good’ at 7 of 9 surveyed reefs.
