Marine
zones
KEY FINDINGS FROM OUR 2025 REPORT CARD
The Townsville Dry Tropics Waterways Report Card tells the story of our waterways from rivers to reef, to show the overall health of aquatic ecosystems. This includes areas off our coastline, such as Cleveland Bay, Halifax Bay, and much further from the coast in the Offshore Marine Zone beyond Magnetic and Palm Islands.
Cleveland Bay water quality remained ‘good’
In the 2023-2024 reporting year, Cleveland Bay waters saw improvements in physical-chemical properties, returning similar results to those two years earlier (before dropping in last year’s Report Card). Phys-chem looks at turbidity and total suspended solids (a combination of inorganic solids like sediment, sand, silt and organic solids such as algae, bacteria, and decaying plant and animal matter). These improvements in phys-chem, resulted in the Cleveland Bay open coastal zone rising from a ‘good’ grade to ‘very good.’
The Magnetic Island Sub-Zone retained a ‘good’ water quality grade. Nutrients improved slightly, but physical-chemical properties and chlorophyll a both dropped from ‘very good’ to ‘good.’
Cleveland Bay enclosed coastal waters also saw a drop in the Chlorophyll a grade, falling from ‘very good’ to ‘good.’
Water quality in Halifax Bay remained ‘good’
Although, declines were seen in Chlorophyll a scores, in two of the three zones. Because chlorophyll a reflects the level of phytoplankton in the water, a low score indicates a rise in phytoplankton populations.
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Phytoplankton are microscopic algae whose growth is closely linked to the availability of nutrients. Measuring chlorophyll a gives a clearer picture of nutrient enrichment than directly measuring nutrients alone.
Higher chlorophyll a concentrations indicate algal blooms, which turn the water green and reduce water clarity, and generally result in a greater abundance of macroalgae on coral reefs close to the coast.
For habitat, which includes seagrass meadows and coral reefs, Cleveland Bay receives a ‘poor’ grade, dropping from ‘moderate’
This drop was driven by seagrass, which saw the health of seagrass meadows decline from ‘good’ to ‘poor,’ mainly due to changes in the density or amount of seagrass growing. However, the overall size of the meadows and variety of seagrass species observed hasn’t changed much, which is favourable for recovery.
The loss in density seen across the region was influenced by widespread environmental pressures, including Severe Tropical Cyclone Kirrily, and periods of cloudy skies, strong winds, and high waves. All of these reduce sunlight reaching the seagrass, and without light, seagrass struggles to grow.
When tough environmental conditions keep happening year after year, seagrass doesn’t get the break it needs to recover.
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Discover more about seagrass in our StoryMap - Guardians of the Bay.
Coral in Cleveland and Halifax Bays have retained the same grades as last year, ‘poor’ and ‘moderate’ respectively
Macroalgae (seaweed) continues to be of concern, with 4 of 7 coral reefs receiving a ‘very poor’ grade again. There were slight improvements at one reef, Pandora South, which saw macroalgae grades increase from ‘very poor’ to ‘poor,’ meaning there was less seaweed at the site than the previous year. And the remaining 2 reefs, retained a ‘very good’ for macroalage. Aside from the improvement at Pandora South, macroalgae results have remained the same at all reefs for the fourth year in a row.
Corals and seaweed compete on a reef, but once macroalgae takes hold, it’s hard for coral to make a comeback. Macroalgae are quick to dominate. Their ability to grow fast and tall, limits sunlight reaching corals already on the reef, and seaweed takes up valuable space needed by baby corals to settle and grow. The number of juvenile corals on all reefs bar one, was graded as ‘very poor’ or ‘poor.’
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Dive into our Corals of the Townsville Region StoryMap, to discover the reefs in Halifax and Cleveland Bays.
Offshore Marine Zone
Coral reefs furthest from the coast, in the Offshore Marine Zone, remained ‘good,’ with the greatest improvements seen at Davies Reef and John Brewer Reef. The later showing signs of recovery following a recent crown-of-thorns starfish outbreak.
It’s important to note, however, that most of the surveys were conducted during the fifth mass bleaching event since 2016 on the Great Barrier Reef. Bleaching is a sign of stress, but corals are still alive and are recorded as live corals. Therefore, the results haven’t captured how many corals recovered or died following the bleaching.
But what the results show is the condition of each reef prior to bleaching. Counts of baby corals remained strong with a ‘very good’ at 7 of 9 reefs surveyed, and 4 reefs had an overall habitat grade of ‘moderate,’ whilst 5 reefs scored a ‘good.’ This provides a valuable baseline to understand impacts of the bleaching event.
Recent survey data for individual reefs and regions can be explored on the Australian Institute of Marine Science’s Reef Monitoring Dashboard. Their coral cover data is taken from manta tow surveys, whilst grades in the Report Card use data recorded during fixed site surveys.
Manta tow surveys observe the standard reef slope habitat around the perimeter of an entire reef, whilst fixed site surveys look at a smaller section of the reef, but in more detail.
