ENVIRONMENTAL
RESULTS
ABOUT THE ZONE
The Mid Harbour zone is the second largest of the harbour zones, and is bounded by Facing, Curtis and Boyne Islands. Most shipping enters the harbour along the Gatcombe channels in the southern end of this zone. The northern boundary of this zone also marks the boundary of the Great Barrier Reef Marine Park.​
WATER & SEDIMENT
The Mid Harbour received an overall water quality score of 0.83 (B).
Sediment quality of the Mid Harbour was very good with an overall score of 0.96 (A).
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The following graphs compare the Water and Sediment scores reported for 2025 (top line) to those from 2024.
WATER
SEDIMENT
Very good (0.85-1.00)
Poor (0.25-0.49)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Very Poor (0.00-0.24)
No data available
Overall, Water quality in Mid Harbour scored 0.83 and received a Good (B) grade, similar to the 2024 Report Card (0.80, Good, B). This score was calculated by aggregating the three sub-indicator and associated measure scores (Physicochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and chlorophyll-a, and dissolved metals – aluminium, copper, lead, manganese, nickel and zinc).
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Mid Harbour received a Very Good (A) grade for pH (1.00), total phosphorus (0.88), a Good (B) grade for turbidity (0.70), and Satisfactory (C) results for total nitrogen (0.50) and chlorophyll-a (0.56). All of the six of the dissolved metals received a Very Good (A) grade, indicating that average concentrations for these measures were within the guideline values for this zone.
For Sediment quality, Mid Harbour received an overall score of 0.96 and a Very Good grade (A), a similar result to the previous year. This score was calculated by aggregating one sub-indicator and associated measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc). The results reflect that all concentrations were below the guideline values for this zone. Arsenic (0.73) received a Good (B) grade, reflecting its natural occurrence within the harbour and may not be associated with anthropogenic inputs.
HABITATS
SEAGRASS RESULTS
Meadow 43
Meadow 48
Mid Harbour has two long-term monitoring meadows adjacent to the south-east corner of Curtis Island. Meadow 43, known locally as Pelican Banks, is the largest (baseline = 632 ha) and most productive (baseline = 19 gDWm-2) seagrass meadow assessed for the Report Card. It is also the only meadow where all three indicators are classed as stable or highly stable. Pelican Banks is an intertidal meadow while Meadow 48 is a subtidal meadow neighbouring the eastern side of Quoin Island.
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Seagrass condition in the Mid Harbour improved to a good (B) due to increases in biomass scores at both Pelican Banks (2024: 0.45, 2025: 0.68) and Meadow 48 (2024: 0.54, 2025: 0.81).
CORALS - ZONE SCORE
The 2025 Gladstone Harbour Report Card scores for the Mid Harbour zone are based on data collected from four reefs: Facing Island, Farmers Reef, Manning Reef and Rat Island. The overall score for Coral in the Mid Harbour zone declined slightly (2024: 0.17, 2025: 0.13) and retained a Very Poor (E).
Coral cover scores at both Mid Harbour reefs remained unchanged from the previous year, with minor variations over the past seven years. Both reefs continue to score Very Poor (E), well below the 40% threshold for a satisfactory grade. Scuba surveys indicate the bio-eroding sponge Cliona orientalis is impacting corals across the harbour, particularly Turbinaria colonies at Seal Rocks South, likely limiting coral recovery.
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Farmers Reef was the only reef to receive a Good (B) grade, although declining from a Very Good (A) in 2024. All other reefs scored a Very Poor grade (E) for the tenth consecutive year.
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Juvenile coral density also stayed Very Poor (E); fast-growing Acropora juveniles, which drove higher cover in 2009, are largely absent, restricting recovery. Change in hard coral cover retained a Very Poor (E) grade for the zone for the third year in the row, although Facing Island retained a Poor (D) grade. Low scores demonstrate that coral communities in Gladstone Harbour are still failing to meet expected recovery levels.
MANGROVE RESULTS
The 2025 Gladstone Harbour Report Card incorporates the 2024 Mangroves results. Mangrove condition has historically remained stable due to strong buffering capacity, and since 2019, monitoring has been undertaken every five years. In 2024, the overall grade for Mangroves in the Mid Harbour declined from Satisfactory (C) in 2019 to Poor (D).
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The mangrove extent sub-indicator, which measures changes in canopy cover relative to saltmarsh and saltpan areas, declined from Poor (D) to a Very Poor (E) grade, including a net loss of mangrove area. The canopy condition indicator, based on remote sensing of canopy density and health, retained a Satisfactory (C) grade. However, shoreline condition, assessed through aerial surveys of mangroves bordering Gladstone Harbour’s water quality zones, improved from a Satisfactory (C) to a Very Good (A) in 2024.
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream A. pacificus. The overall score for 2025 was higher than the previous year (2024: 0.54, 2025; 0.69) and improved from a Satisfactory (C) to a Good (B) grade. This is a result of increased catch numbers of Yellowfin bream (2024: 4, 2025: 6), though Pikey bream declined (2024: 8, 2025: 10) bream.