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 ENVIRONMENTAL 
RESULTS 

Gladstone Healthy Harbour Partnership GHHP report card

AREA: 95.73 km2

 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. This zone contains two monitored seagrass meadows, including the largest seagrass meadow in the harbour at Pelican Banks. Within the zone, coral reefs occur along the western side of Facing Island and on the south-east tip of Curtis Island. The northern boundary of this zone also marks the boundary of the Great Barrier Reef Marine Park.

This zone has six water and sediment monitoring sites, two monitored seagrass meadows, four coral monitoring sites, two fish monitoring sites and three mangrove monitoring sub-zones.

Gladstone Healthy Harbour Partnership GHHP report card

 WATER & SEDIMENT 

The Mid Harbour received an overall water quality score of 0.82 (B). 

Sediment quality of the Mid Harbour was very good with an overall score of 0.97 (A).

The following graphs compare the Water and Sediment scores reported for 2023 (top line) to those from the previous year.

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)

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No data available

Overall, Water quality in Mid Harbour scored 0.82 and received a good grade (B), similar to the 2022 report card. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physiochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminum, copper, lead, manganese, nickel and zinc).


Within the Physiochemical sub-indicator, Mid Harbour received a score of 1.00 and a very good grade (A) for pH indicating that the average pH was well below the guideline value. This zone received a score of 0.58 and a satisfactory grade (C) for turbidity indicating that average turbidity was within the guideline value range. 


Within the Nutrient sub-indicator group, total nitrogen (0.63) received a satisfactory grade (C) indicating concentrations for this measure were within guideline values. In contrast, total phosphorus (0.71) and chlorophyll-a (0.65) received good grades (B), indicating that average concentrations for these measures were below the guideline values.


All six Dissolved metals received high scores (1.00) and very good grades (A) indicating that average concentrations were well below the water quality guideline values.


For Sediment quality, Mid Harbour received an overall score of 0.97 and a very good grade (A), also 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).


In 2023, six of the seven Metal and metalloid sub-indicator measures received very high scores (1.00) and very good grades (A), while one measure – arsenic – received a score of 0.82 and a good grade (B). These results reflect that all concentrations were below the guideline values.

Gladstone Healthy Harbour Partnership GHHP report card

 HABITATS 

SEAGRASS RESULTS

Meadow 43

Meadow 48

Mid Harbour has two monitored meadows adjacent to the south-east corner of Curtis Island. Meadow 43, known locally as Pelican Banks, is the largest and most productive 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 (Meadow 43) is an intertidal meadow while Meadow 48 is a subtidal meadow neighbouring the eastern side of Quoin Island. 

The overall condition of the Mid Harbour Seagrass was graded satisfactory (C) with a score of 0.57. This is a decrease from the previous report card (2022: 0.67; good grade, B). In Meadow 43, changes in species composition from the foundation species Z. muelleri ssp. capricorni (the species which were abundant during the 2022 report card reporting period), to small less persistent Halodule uninervis and Halodule ovalis during this period contributed to the lower meadow biomass score. Additionally, Meadow 43 is subject to high levels of herbivory from dugongs and turtles that may be altering the species composition and restricting recovery. Although there was a small decline in scores, the overall grade for Meadow 48 was good (B) the same as the previous year. 
 

CORALS RESULTS

The 2023 Gladstone Harbour Report Card scores for the Mid Harbour 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 was 0.15 and graded very poor (E), indicating a very poor condition. 


Compared to the 2022 results, coral cover scores increased marginally at Manning Reef, decreased in Rat and Facing Islands and remained the same at Farmers Reef. Minor score variations have been observed over the past six years; however, these scores are still substantially lower than the 40% threshold required to receive a satisfactory grade (C) with both harbour zones graded very poor (E) for coral cover. 


Scuba surveys indicated that the bio-eroding sponge Cliona orientalis continues to impact the coral community across the whole harbour and in particular, colonies Porites and Cyphastrea on reefs in the Mid Harbour zone. Sponge prevalence is likely contributing to a lack of coral cover recovery across the harbour. 


Farmers Reef was the only reef to receive a satisfactory grade (C) for macroalgae cover due to an improved score from the previous year (2022: 0.28, 2023: 0.56), indicating lower macroalgae cover. All other reefs scored a very poor grade (E) for the eighth consecutive year. Macroalgae communities are more variable at reefs in the Mid Harbour zone, where cover and composition vary both from year to year. In 2023, communities at the four Mid Harbour reefs were dominated by the red macroalgae Asparagopsis or the brown macroalgae Lobophora


The harbour-wide density of juvenile corals has continued to decline, receiving a very poor grade (E) for the fifth consecutive year. Farmers Reef and Rat Island were the only reefs to increase scores compared to the previous year (2022: 0.27 and 0.07, 2023: 0.31 and 0.10, respectively) although grades remained consistent. All other reefs decreased scores and remained with very poor grades (E). High coral cover in 2009 was linked to abundant representation of Acropora juveniles a fast-growing, branching coral; however, in 2023, this juvenile family was notably lacking across the harbour. Recovery of corals may be limited until this family appears and survives.


Overall, in Gladstone Harbour changes in hard coral cover has been graded poor (D) for the past six years. In 2023, the change in hard coral cover score for the Mid Harbour (0.22) declined and was graded very poor (E) for the first time since 2017. In general, the ongoing low scores and very poor grades demonstrates recovery of coral communities continues to fall short of modelled expectations.

MANGROVE RESULTS

No mangrove assessment was conducted in 2023, results are from monitoring conducted in 2019. The overall zone score for the Mid Harbour was 0.55 (C) indicating a satisfactory condition for mangroves in this zone. This was a result of a poor score for mangrove extent (0.39), and satisfactory scores for canopy condition (0.63) and shoreline condition (0.63).

This overall score for 2019 was identical to the score recorded in 2018. 

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 FISH & CRABS 

 FISH RECRUITMENT RESULTS 

Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall score for 2023 was lower than the previous year (2022: 0.57, 2023: 0.49) and declined one grade to

poor (D). This decline in score is a result of a decrease in number of bream caught during the 2022–23 reporting period

(2022 report card: 15 fish, 2023 report card: 11 fish).

Fish health is assessed though two sub-indicators, Fish condition and Fish Health Assessment Index (HAI). 
The overall score for Fish health in 2023 was 0.81 and received a good grade (B). The 2023 results were calculated by the average of the Fish HAI score (0.90; results carried over from 2021) and new assessment of Fish condition which scored similar to the previous year (2022: 0.74, 2023: 0.73).  
 

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