Great Barrier Reef

Water quality remains a significant and ongoing threat to the site, with land-based runoff—particularly sediment, nutrients, and pesticides—continuing to degrade coastal and inshore ecosystems and compounding the impacts of climate change. The 2021–2022 Reef Water Quality Report Card underscores this challenge, reporting very poor progress towards the dissolved inorganic nitrogen (0.7%) and sediment (0.8%) reduction targets. In contrast, very good progress was achieved for particulate phosphorus and moderate progress for particulate nitrogen. Notably, the Burdekin catchment saw a 3% reduction in dissolved inorganic nitrogen due to improved sugarcane growing practices, while sediment reductions of 5.3% in the Murray (Wet Tropics) and Endeavour (Cape York) catchments were linked to streambank repair and improved grazing land management—bringing the Murray catchment to its target for the first time. Pesticide risk conditions remained largely unchanged, though improved in the Murray, likely due to drier conditions. Loss of riparian vegetation totalled 47,519 hectares (0.78%) between 2018 and 2021, primarily in the Burdekin, Fitzroy, and Burnett Mary regions. Wetland loss slowed (<0.05%), and freshwater floodplain wetlands were generally in good condition but under moderate pressure. Inshore marine condition remained moderate, with coral in poor condition, seagrass improving to moderate, and water quality declining to moderate. Importantly, grazing land ground cover targets were met for the first time since 2012, helped by above-average rainfall across all regions.

The 2022 Scientific Consensus Statement (SCS), released in August 2024 (Waterhouse et al. 2024), brings together the latest scientific evidence to understand how land-based activities are influencing water quality in the Great Barrier Reef (GBR), and how these influences can be managed to improve water quality outcomes for the GBR. The SCS made eight overarching conclusions. The first five of these are:
1. Historical and continuing land management and catchment modification impair Great Barrier Reef water quality through extensive vegetation degradation, changed hydrology, increased erosion, and expansion of fertilised land uses, urban centres and coastal developments.
2. Pollutant loads from the catchment area to the Great Barrier Reef have increased from pre-development loads by 1.4 to 5 times for fine sediments, and 1.5 to 3 times for dissolved inorganic nitrogen (with variations depending on basins).
3. Poor water quality, particularly elevated levels of fine sediments, nutrients and pesticides, continues to have detrimental impacts on Great Barrier Reef ecosystems. The greatest impacts are on freshwater, estuarine, coastal and inshore marine ecosystems.
4. Human-induced climate change is the primary threat to the Great Barrier Reef and poor water quality can exacerbate climate-related impacts. Good water quality is critical for healthy and resilient ecosystems and supports recovery from disturbances such as mass bleaching and extreme weather events. Meeting water quality improvement targets within the next ten years is imperative.
5. While several land management practices and remediation actions are proven to be cost-effective in improving water quality, translating these into more substantial pollutant reductions will require significant scaling up of the adoption of these actions, prioritisation of pollutant hotspots, and greater knowledge of the costs and potential co-benefits of practice adoption.

Furthermore, in February 2025, a severe weather event in north Queensland has carried vast amounts of river discharge affecting approximately 50,000 km² of the reef – stretching across inshore, mid-shelf, and outer reefs as well as seagrass meadows and other marine ecosystems. Satellite imagery shows major flooding across nearly every river basin from Cairns to Mackay; plumes from 10 major river basins merged to form extensive and widespread flood plumes, extending more than 700km along the coastline and 100km offshore in some places (James Cook University, 2025). The Burdekin River, one of the largest contributors to flood plumes on the GBR, recorded its biggest peak flood discharge since 2009. Such flood plumes result in prolonged low light and sediment build-up that can smother seagrass and weaken corals, increasing their vulnerability to bleaching and disease. Elevated nutrients are also carried into the marine environment leading to higher levels of macroalgae overgrowth on coral reefs, lower coral coverage, and less new coral growth. Sediments delivered by the plume can remain active for months after the flood event and can cause prolonged reductions in water clarity.

Assessment of land clearing trends—based on satellite monitoring through the Statewide Landcover and Trees Study (SLATS)—shows some progress. A report released in December 2022 showed overall broadscale clearing in 2019–20 fell by nearly 40 per cent state-wide and 16 per cent in reef catchments from the previous year. A subsequent report released July 2024 shows overall clearing in 2021–22 fell another 7 per cent statewide and 13 per cent in reef catchments. This is a total reduction of nearly 23 per cent statewide and 21 per cent in reef catchments in two years. It is important to note that 78 per cent of this overall clearing was re-clearing of areas that had previously been lawfully cleared. Vegetation in riparian areas is important for water quality as it increases streambank stability and helps intercept overland flows, preventing sediment and nutrient generation from erosion. The Reef Water Quality Report Card 2021 - 2022 released in May 2024 showed limited progress towards the target overall with 47,519 hectares (0.78%) cleared during this period. Most of this loss occurred in the Fitzroy, Burnett Mary and Burdekin regions.

Preliminary mapping of all reef catchments has been delivered through the Queensland Gully and Streambank Mapping Program and enhanced mapping of the high priority catchments is complete. This will inform the prioritisation of future investment primarily through its application in the Reef Report Card water quality catchment models.

Outbreaks of crown-of-thorns starfish (COTS) remain a serious threat affecting reefs across the GBR Region. The causes of COTS outbreaks on the GBR are complex, and the exact combination of factors that lead to primary COTS outbreaks are not fully understood (Caballes et al., 2024; Pratchett et al., 2017). In addition to the influence of nutrient run-off, fishing pressure, coral prey availability, oceanographic circulation patterns and reduced predation (Pratchett et al., 2017; Sweatman, 2008), temperature has been shown to affect reproduction and settlement of COTS (Caballes et al., 2021). COTS therefore remain the subject of ongoing research interest.

Since 2019, a build-up of COTS at Lizard Island (Chandler et al., 2023) and Cape Grenville (Pratchett et al., 2022) has been identified and is thought to represent the start of a new primary outbreak. Increasing evidence suggests that the Swain Reefs, Cape Grenville and Townsville–Innisfail sectors (Matthews et al 2020; Brodie et al 2017) are particularly susceptible to COTS outbreaks and may play crucial roles in overall outbreak wave dynamics or initiation.

Active management of COTS outbreaks has become more effective over the past decade due to various improvements, including adopting an integrated pest management approach (Westcott et al., 2021), developing a single shot injection technique, advances in computer-aided modelling and prediction, and increasing vessel capacity.

In 2018, funding for the COTs Control Program was increased enabling the program to expand from two to six vessels, meaning control vessels could be deployed in the far north and far south of the GBR for the first time. Since 2019, increased effort has led to the suppression of outbreaks at both individual reef and regional scales, and new evidence demonstrates that the control program is minimising coral loss at target reefs, making the COTS Control Program more strategic and effective than previous control programs on the GBR. The programme has been successful in holding the densities of COTS below set thresholds on 75% of 57 priority reefs between Port Douglas and Townsville (State Party of Australia, 2019). However, COTS outbreaks continue to be most severe in the Southern Region (Swain Reefs) and between Port Douglas and Lizard Island. Isolated and less severe outbreaks are persisting offshore Townsville and the Whitsundays.

The COTS Annual Report Dashboards are available online, and provide an overview of the COTS Control Program and delivery outcomes, COTS outbreaks and coral cover status across all reefs actioned by the Program.

The Queensland and Australian Governments have made progress in addressing fisheries-related management actions since the last IUCN Outlook in 2020, particularly in response to the 2022 Reactive Monitoring mission. Substantial management changes have been implemented through the Sustainable Fisheries Strategy 2017-2027 (SFS), as well as additional regulatory changes to protect snapper, pearl perch and Spanish mackerel. The SFS Year 7 progress report identifies that 30 of 33 actions have been delivered by 2023-2024. Significant reforms in 2024 removed gillnet fisheries from the Great Barrier Reef World Heritage Area (GBRWHA), significantly reducing risk to particular threatened, endangered and protected species.

Queensland’s fisheries are managed under a sustainability framework, and key fish stock assessments indicate favourable outcomes. About 93% of fish stocks are considered to have no sustainability concerns. In comparison, 7% are depleted or depleting and have rebuilding strategies in place with targeted conservation and fisheries management interventions to aid recovery.

Notably, there has been significant progress in phasing out large mesh gillnet fishing in the GBRWHA, with the vast majority of associated licences now compulsorily retired. Research has demonstrated that the GBR’s no-take zones significantly enhance fishery sustainability by contributing nearly half the coral trout catch via larval dispersal and spill over of mature fish (Bode et al., 2025), underscoring the value of spatial protection strategies. This commitment therefore marks an important step forward. Smaller mesh nets (Queensland Fisheries Symbol N11 and bait collection nets), which also pose bycatch risks to threatened species, remain permitted throughout the GBR World Heritage area. While these nets present a lower risk profile than large mesh gillnets, and do not have the same potential to interact with bycatch or threatened, endangered, and protected species, their use within the property may require further evaluation using an evidence based approach to ensure that the use of these nets does not damage the OUV. A transitional gillnet fishery (remaining 28 ‘NX’ licences) will operate under strict conditions, including electronic monitoring, until June 2027.

Further progress in implementing the Queensland Government’s Sustainable Fisheries Strategy (SFS) has fallen behind schedule. Key actions, such as rolling out independent monitoring, are significantly delayed (IUCN Consultation, 2025) and conditions have been amended with independent monitoring and validation to commence implementation by 15 December 2025. The Queensland government was granted an extension to its Wildlife Trade Operation, originally due by May 2024, of a validated and quantitative data collection system in the East Coast Otter Trawl Fishery. Stock assessments, which are critical for sustainable fisheries, have also proven difficult to maintain at the planned frequency. As a result, some 2027 SFS targets appear unlikely to be met, especially those concerning rebuilding fish stocks, avoiding overfishing, and maintaining Wildlife Trade Operation accreditations. However, significant progress has been made in the last 12 months with completion of the Onboard Monitoring Field Trial, and establishment a federal funding agreement to support Sustainable Fisheries and Marine Animal Protection.

At present, several fish stocks remain overfished or depleted, and remain open to fishing within the GBR despite their status. The Queensland Sustainable Fisheries Strategy stipulates that fisheries should close if stocks fall below 20% of unfished biomass, which must be enforced in order to conserve the site's OUV.

Further concerns relate to the overall responsiveness and implementation of harvest strategies across several GBR fisheries. In some cases, decision rules that would warrant more precautionary action have been triggered, such as in the Reef Line Fishery, but corresponding management responses have not followed (IUCN Consultation, 2025). Similarly, key strategies in the East Coast Inshore Fishery have not been updated following major changes to gillnet fishing, raising questions about alignment between harvest methods and regulatory frameworks.

Despite increased investment in fisheries management, ensuring compliance remains challenging. While mandatory electronic monitoring has been introduced for NX gillnet vessels, verifying the fate of bycatch, particularly its condition upon release, remains a challenge. Independent data validation in the trawl fishery has also progressed slowly, even as underreporting of interactions with threatened species (e.g., sea snakes) continues (Australian Marine Conservation Society & WWF-Australia, 2025).

The establishment of net-free zones (NFZs) in key dugong habitats has provided some added protection for threatened species. However, smaller mesh gillnets remain permissible within these areas, and other biologically significant habitats remain open to large mesh gillnet use until the full transition is completed in 2027. Once fully removed, these nets’ phase-out is expected to improve outcomes for many vulnerable species. Otter trawling is permitted in approximately 34% of the property, although this area is not all viable and economic fishing area. The 2024 GBR Outlook Report highlighted intensive trawl activity in deep areas of the outer southern Reef, where several species remain at high risk from trawling, according to a 2023 Queensland ecological risk assessment.

Meanwhile, in the Queensland Coral Fishery, 200,052 kg is available in the coral fishery through individual transferable quota across 9 categories. An additional 88,422 kg is available through competitive commercial catch limits. Under quota arrangements 40,687.65 kg was landed in the 2023-2024 financial year (20.34% of the limit), and 21,428 kg was landed under the competitive catch limits (24.23% of the limit). While 2022 reforms introduced species-specific quotas and restrictions on CITES-listed species, concerns remain about the fishery’s ecological effects, including potential localised depletion and risks to endemic species. International scrutiny has increased: the UK banned all coral imports from the fishery in 2021, followed by the EU’s 2022 ban on five coral species. Many harvested species are particularly vulnerable to climate-induced bleaching, and recent studies confirm the high thermal sensitivity of some of the fishery’s most valuable target species.

Recreational fishing pressure also continues to grow. While it must be noted that not all recreational vessels are fishing, between 2008 and 2024, the number of registered recreational vessels in Queensland increased by almost 40,000 to a total of 261,290 (Qld Dept of Transport and Main Roads, 2025). Enhanced access to GPS and sonar technology has expanded fishing effort—particularly in inshore zones—raising concerns about cumulative impacts on key habitats. However, it should also be noted that permit fees are used to restock 3 million native and threatened fish in over 60 waterways.

Overall, it is important to note the progress made in reducing the threat of fishing in the site, including the phase-out of large mesh gillnets and reforms under Queensland’s Sustainable Fisheries Strategy. However, key challenges remain, such as delays in independent monitoring, gaps in harvest strategy implementation, and continued fishing of overfished stocks. As highlighted by Baker et al. (2024), fisheries management is only partially effective in delivering outcomes, and while this remains the case, the threat posed by fishing remains high.

Compared to other threats, direct impacts from tourism remain low. The marine tourism industry is a key partner in the protection and management of the Great Barrier Reef. Many tourism operators ensure their activities are best practice by following the Responsible Reef Practices for tourism operators. High Standard Tourism Operators voluntarily operate to a higher standard than required by legislation as part of their commitment to ecologically sustainable use. These operators are independently certified as meeting best practice standards for the key areas of protection, presentation and partnership. Nonetheless, some impacts from tourism, and recreational activities in general, occur and include direct impacts through anchor damage, vessel groundings, boat strikes, damage to corals by divers and snorkellers, disturbance of wildlife, emissions from vessel operations, as well as potential indirect impacts, such as the potential for the introduction of invasive species (GBRMPA, 2019a).

Between 2019-22, some three thousand ships transited through the region, making approximately 11,000 separate voyages each year (GBRMPA, 2024). These ships include trade vessels (bulk carriers, gas tankers, container carriers, vehicle carriers, general cargo ships) and non-trade vessels (cruise ships, superyachts, tug and tows, naval vessels). The region is home to four active cruise ship berths (Bundaberg, Gladstone, Townsville and Cairns), and many cruise ship anchorages, with an annual demand forecast of up to 150 cruise ships through the Port of Cairns (GBRMPA, 2024).

The Australian Maritime Safety Authority (AMSA), along with the Great Barrier Reef Marine Park Authority and Maritime Safety Queensland, regulate shipping activities in the GBR by administering special measures under international and domestic law. These measures include designated shipping areas, navigation markers, compulsory pilotage, mandatory vessel monitoring and reporting, ship routing and shore-based monitoring. The operation of the GBR and Torres Strait Vessel Traffic Service (Reef VTS) now covers the entire GBR Region, providing 24-hour monitoring and tracking of all shipping traffic within the region. This service can divert ships in the event of a traffic conflict, intervene to prevent a maritime incident, monitor maritime incidents, support investigations of potential breaches of legislation, and support effective response to incidents. Emergency response arrangements include an emergency towing vessel that responds to stricken ships, pollution, and search and rescue operations.

Shipping activities in the GBR are further managed under a comprehensive regulatory framework including the Transport Infrastructure Act 1994, which supports integrated planning of transport infrastructure, and the Transport Operations (Marine Safety) Act 1994, which balances marine safety regulation with maritime industry efficiency. The Transport Operations (Marine Pollution) Act 1995 and associated regulations give effect to MARPOL Annexes I–V in Queensland waters, managing discharges such as oil, noxious liquids, garbage, sewage, and ballast water. For Annex VI (air pollution), federal legislation under the Protection of the Sea (Prevention of Pollution from Ships) Act 1983 applies. Port-specific protocols, including the Queensland Coastal Contingency Action Plan and First Strike Response Deeds, provide detailed oil spill response procedures.

Threats from shipping include greenhouse gas emissions, ship groundings, vessel strikes on megafauna (especially whales), waste discharge, spread of invasive marine species, oil spills, marine debris, propellor wash causing the resuspension of sediment (especially when operating on low tides), antifoulant paint and noise pollution. Smith et al. (2020) predicts a three- to five-fold increase in risk to humpback whales from ship strikes over the next ten years.

To address the risk of vessel strikes, national guidance and strategies have been developed, including the National Strategy for Reducing Vessel Strike on Cetaceans and Other Marine Megafauna. The Reef VTS system, compulsory pilotage areas, and routing measures also contribute to vessel strike mitigation.

Management of biosecurity threats from invasive marine species is shared across jurisdictions, with ports designated as First Points of Entry under the Biosecurity Act 2015 (Cth). In Queensland, all individuals and entities have a general biosecurity obligation under the Biosecurity Act 2014. The Queensland Seaports eDNA Surveillance (Q-SEAS) program, jointly implemented by ports and Biosecurity Queensland, provides early warning detection using cutting-edge molecular methods and has received national recognition.

Noise pollution from shipping is being addressed through initiatives such as underwater noise monitoring (e.g., Port of Townsville Channel Upgrade Project), participation in the Environmental Ship Index and NEPTUNES voluntary reporting programs, and the work of Ports Australia’s Noise Subcommittee. This includes collaboration on the development of National Anthropogenic Underwater Noise Guidelines and international standards for ship noise reduction.

The North-East Shipping Management Plan (North-East Shipping Management Group, 2019) provides the framework for the management of risks, and complements the Reef 2050 Plan. Since 2014, five oil spills from ships have been reported, one being a moderate-size oil spill and four minor ones (GBRMPA, 2019a). The latest comprehensive assessment of impacts of ship anchorages was undertaken in 2013, but it is estimated that impacts remained at the same level given that shipping traffic has been maintained at similar levels (GBRMPA, 2019a).

Additional management responses include sediment resuspension mitigation through routing, timing of vessel transits, and operational procedures at ports. The use of antifoulant paints is subject to international and national controls under MARPOL and domestic regulation, limiting harmful substances. Furthermore, measures to manage marine debris include strict garbage discharge regulations under MARPOL Annex V, with discharge distances from nearest land defined for the GBR outer boundary.

The catchments, coastline and islands of the region occupy a wide range of different land uses but grazing and cropping are dominant. Many of the important agricultural industries in the catchment are at historical highs, particularly beef, bananas and cotton, which have all recorded their highest annual production numbers and land use areas since 2010 (GBRMPA, 2024). The area under cropping has declined in the Fitzroy and Mary-Burnett catchments but has increased in other reef catchments and are at or around their historical maximums (GBRMPA, 2024). The catchment includes the Bowen Basin, which is the most commercially valuable coal-bearing region in Queensland. In 2021–22, of the 54 operating coal mines in Queensland, 49 were in the reef catchment producing 135.4 million tonnes of metallurgical coal and 68.6 million tonnes of thermal coal. Between 2015–16 and 2022–23, the number of development licences for coal increased slightly (GBRMPA, 2024). Population growth drives coastal development and population growth is higher in the GBR region than anywhere else in Australia (GBRMPA, 2024). In June 2022, the catchment population was 1.25 million and is expected to rise to 1.53 million by 2046. The growth of coastal communities generates a variety of impacts, including increased recreational fishing and other direct uses of the region, coastal development, and land-based runoff. Coastal infrastructure, such as roads, marinas and boat ramps, housing development and the demand for more urban support services, such as sewage and stormwater treatment and energy infrastructure, will increase with an expanding population (GBRMPA, 2024).

Twelve ports are located in the GBR region, and all come under the Sustainable Ports Development Act 2015 (Qld). Five of these ports (Gladstone, Hay Point, Mackay, Abbot Point and Townsville) have been designated as priority ports under the Queensland legislation. Four other ports are also significant for specific purposes (i.e. Cairns, Cape Flattery, Lucinda, Mourilyan) along with three smaller community ports. These ports provide vital links between Queensland, the rest of Australia and the world enabling the export of agricultural and mineral commodities (especially coal), the import of goods (such as petroleum, cars and household items that sustain regional communities) as well as supporting commercial tourism (especially cruise ships), defence activities and local communities.

Many of these ports periodically maintain or improve their maritime port infrastructure, which includes maintenance dredging, and in some cases, capital dredging programs. All dredging and material disposal activities in the region’s ports are managed under both Queensland and Commonwealth legislation. Maintenance dredging requirements depend on the local port characteristics, and the total amount of reported maintenance dredge material removed from the GBRWHA between 2019 and 2023 (approximately 6.2 million cubic metres) was 1.5 times that for the preceding 5 years (GBRMPA, 2024). Since 2019, three key capital dredging campaigns have occurred within the ports of Cairns, Townsville and Gladstone. A total of 4.99 million cubic metres of capital dredge material was removed, with that material being used for port reclamation works.

Extension of existing ports through reclamation and dredging continue to pose locally significant threats to the OUV of the property. Impacts from such port developments include loss and degradation of critical habitat for marine megafauna; fragmentation of dugong, turtle and dolphin populations through habitat loss and degradation; subsequent resuspension of maintenance dredge spoil from shallow dumping grounds and the impacts of the actual dredging leading to plumes which then have adverse consequences for nearby habitats including fringing reefs.

The impacts from port activities therefore range from direct removal of habitat, for example, by capital and maintenance dredging of the seafloor, to reclamation of port waters, through to indirect environmental impacts, such as intermittent noise pollution, spills (cargo and pollutants) and light pollution from port infrastructure. While some of these impacts associated with port operations have been reduced, others persist, for example direct impacts continue to occur from coal dust contamination which escapes as coal is transferred between train and ship (GBRMPA, 2019a; 2024). Impacts of additional coastal development also remain of concern, as has been highlighted in the Reef 2050 Plan and the Scientific Consensus Statement (Waterhouse et al., 2017 and 2024; Schaffelke et al., 2017).

Diseases are known to have affected a number of organisms, including corals, turtles, dolphins, urchins, sponges, molluscs, seagrasses, fishes and crabs. For example, at least 8 different coral diseases have been reported in the region. White spot disease can cause mortality in crustaceans; while there are no known occurrences in the World Heritage property, the disease was found in wild crustaceans in northern Moreton Bay in 2020. The H5N1 bird flu has not yet been found in Australia, despite the virus being found on every other continent (Australian Government, 2025). Its presence in Australia could have catastrophic impacts on many bird populations in the World Heritage property. The Australian government is working collaboratively with the Queensland and other state and territory governments to enhance preparedness and national response capabilities. The prevalence of coral disease and disease outbreaks are frequently linked to environmental stress, including rising sea temperatures, storm events, decreased water quality and nutrient enrichment (GBRMPA, 2024). Predators can also affect coral disease by damaging protective tissues and exposing corals to infections, transmitting diseases between corals, or acting as reservoirs for pathogens (GBRMPA 2024). Increased susceptibility is caused by stress from both acute and chronic influences. Marine turtles suffer from various pathogenic diseases, and there may be links between immunosuppression and exposure to environmental pollution. However, disease has only been attributed as the cause of death in a small number of stranded marine turtles in the past 5 years (GBRMPA, 2024). High disease rates in some commercially caught coral trout in 2016 may have been influenced by heavy bleaching on source reefs. With increasing global warming and poor water quality, disease prevalence may also increase in fish species. Consequences will vary depending on the disease and duration of outbreak but could have major effects at a broad scale (Brodnicke et al. 2019; GBRMPA, 2019a).

Climate change poses the biggest threat to the long-term conservation of the Great Barrier Reef (GBR) and its OUV (GBRMPA, 2019a; 2024). Of most concern are ocean warming, the increasing frequency and intensity of extreme weather events, and acidification. The back-to-back coral bleaching that occurred in 2016 and again in 2017 was unprecedented, impacting the upper two-thirds of the length of the GBR. The 2020 bleaching was severe and the most widespread ever recorded (ARC Centre for Coral Reef Studies, 2020; GBRMPA, 2020). 25% of coral reefs overall were severely impacted – more than 60% of corals were bleached, with 25% of reefs severely impacted (GBRMPA, 2020).This followed the highest monthly sea surface temperatures (in February) ever recorded on the GBR since the Bureau of Meteorology’s records began in 1900. The proportion of severely bleached reefs in 2020 was exceeded only by 2016, and 2020 was, at the time, the second-worst mass bleaching event of the five experienced on the Great Barrier Reef since 1998.

The 2022 coral bleaching event was the first mass bleaching event on the GBR during the La Nina phase of the El Niño-Southern Oscillation (ENSO). Historically, these produce cooler summer conditions on the GBR, with higher rainfall and higher cloud cover. Severe bleaching (more than 60% of community coral cover bleached) affected 43% of reefs surveyed (AIMS, 2024). Worst affected was the Central region of the GBR, where the most heat stress occurred. The majority of the reefs bleached were exposed to moderate levels of heat stress (NOAA Degree Heating Week 5-8°C-weeks), which has been linked to bleaching but with lower levels of mortality.

From January to March 2024, a summertime marine heatwave (prolonged above average water temperatures) led to the fifth mass coral bleaching event on the GBR since 2016. The 2024 event, which was part of the fourth global mass bleaching event, had the largest spatial extent of bleaching recorded to date on the GBR, spanning all three regions (Northern, Central and Southern) (Cantin et al. 2025). In January 2025, sea surface temperatures were 1 to 2ºC above average, with the highest temperature anomalies recorded in the Northern and Central regions, leading to bleaching-level heat stress accumulations. There was some reprieve in February with the arrival of monsoonal cloud and rain but in mid-March 2025, sea surface temperatures increased in the Far Northern region to 1.1ºC above average. In contrast, temperature anomalies remained steady in the Northern region (0.8ºC) and the Central region (0.4ºC) above average.

The GBR has recently been impacted by three tropical cyclones. Cyclone Jasper in December 2023 (Category 5 – but only Category 2 when traversing the GBR) and Cyclone Kirrily in January 2024 (Category 3) impacted the Central GBR. In early March 2025, severe Tropical Cyclone Alfred caused severe wind and wave conditions in the eastern part of the Southern GBR Region. Temperatures dropped in the Southern region in the wake of Cyclone Alfred but were still 0.3ºC above the long-term average. North Queensland continued to be inundated by heavy rainfall in February-March 2025, with many local communities already recording their highest ever monthly rainfall totals. In February, major to moderate flooding levels occurred across nearly all river basins between Cairns and Mackay. Satellite imagery showed extensive and significant flood plumes from all affected river systems extending more than 700 km along the coastline, spread across inshore, mid-shelf and outer reefs, seagrass meadows and other marine ecosystems (James Cook University, 2025).

A recent report by AMCS and WWF (2025) summarised the impacts of such extreme weather events – mass coral bleaching and two tropical cyclones - on the GBR during the summer of 2023-24, utilising recent in-water observations (i.e., to 10 February 2025) from the Australian Institute of Marine Science (AIMS) website. The AIMS website divides the GBR into 11 sectors for monitoring purposes; some of the monitoring results are “complete” and others are “in progress”. The full suite of results are on the website, but the AMCS & WWF report (2025) highlights the following concerns:
• Princess Charlotte Bay: a relative decline of ~23% in hard coral cover between 2024 and 2025.
• Cooktown / Lizard Island: hard coral cover was down from 31.5% in 2024 to 21.0% in 2025; a relative decline of 33% in coral cover. Mortality during the 2024 mass coral bleaching event caused the single largest annual decline in sector-wide hard coral cover since surveys began.
• Cairns: hard coral cover was down from 34.4% in 2024 to 22.1% in 2025; a relative decline of nearly 36% in coral cover. The combined impacts of the 2024 mass coral bleaching event and Tropical Cyclone Jasper produced the largest annual sector-wide decline hard coral cover since monitoring began.
• Pompey: Coral bleaching was recorded on the majority of surveyed reefs, although the level of bleaching varied within and among reefs, ranging from 0% to 100%. Surveys are continuing.
• Capricorn Bunker: hard coral cover was down from 56.2% in 2024 to 33.1% in 2025; a relative decline of 41% in coral cover. The mass coral bleaching event, storm swell impacts, and coral disease have caused the single largest annual decline in hard coral cover for this sector in 39-years.

As the principal cause of decline in coral cover on the GBR is temperature driven, the above impacts point to the need for urgent action to drastically reduce global greenhouse gas emissions to safeguard the OUV of the world’s largest coral reef ecosystem.

Marine debris, especially plastics, is a cause for concern due to its abundance, durability and persistence in the marine environment, and its consequent environmental, economic, aesthetic and human health impacts. Ocean currents transport marine debris throughout the world’s oceans making the GBR region vulnerable to debris derived from a combination of marine and land-based sources (Kroon et al., 2020). Likely sources include commercial fishing boats, large commercial, military and recreational vessels, sewage and storm water, industrial facilities including aquaculture, tourism boats and coastal tourism activities, recreational visitors and beachgoers, and riverine transport of waste from landfills and other inland sources (GBRMPA, 2024).

The quantity and relative contributions of types of marine debris collected along the GBR’s coast and islands vary from north to south. Smaller plastic particles, including microplastics (less than 5 millimetres) are consistently detected in GBR surface waters and can represent up to 50 per cent of marine debris in some areas (GBRMPA, 2024). Remnant plastic pieces (hard and solid) (227,395 items) and plastic lids and tops, pump spray and flow restrictors (100,430 items) remained the most common categories of debris collected from 2019 to 2022 (Tangaroa Blue 2023). In addition to plastics, other items, such as glass, rubber, and foam comprise a substantial proportion of total debris found in Australian waters, both in coastal and offshore areas (GBRMPA, 2024).

There is a regulatory framework in place to manage ship-sourced pollution in Queensland. Australia is party to all six annexes of the International Convention for the Prevention of Pollution from Ships (MARPOL), the main international convention for addressing ship sourced pollution including oil, noxious liquid substances, packaged harmful substances, garbage, sewage, and air pollution. The Australian Maritime Safety Authority (AMSA) give effect to MARPOL in Australia though the Protection of the Sea (Prevention of Pollution from Ships) Act 1983. This includes roll back provisions for states and territories to give effect to MARPOL in their coastal waters. Queensland gives effect to Annexes I to V in the Transport Operations (Marine Pollution) Act 1995 (TOMPA) and Regulation 2018 (TOMPR).

For limited types of garbage permitted to be discharged to sea under Annex V (such as food scraps), as well as a number of other waste types across other Annexes, discharge provisions are generally set as a minimum distance from nearest land. For discharge purposes, MARPOL defines nearest land for North East Australia by coordinates which are generally the outer boundary of the Great Barrier Reef.

More than 250 non-native marine species have been recorded in Australian waters, though this figure is likely an underestimate due to the difficulty of detecting cryptic or morphologically similar species. Introduced terrestrial and freshwater species are also present in the GBR catchment (GBRMPA, 2024; DAFF, 2024).

In December 2022, the white colonial sea squirt (Didemnum perlucidum) was detected for the first time on tourism infrastructure within reef habitat in the Great Barrier Reef Marine Park, specifically at Moore Reef offshore from Cairns. Although the species has been known in major Queensland ports for at least five years (and in other Australian jurisdictions for over a decade) this detection, which was self-reported by a tourism operator, marked its first known occurrence in reef habitat. The Reef Authority established an incident management team to work with tourism operators, Gunggandji Traditional Owners, and other partner agencies to determine the nature and extent of the outbreak, with the results informing a management response. Due to the species’ high reproductive capacity and rapid growth, complete eradication is not considered feasible (GBRMPA, 2024).

Since 2019, two additional non-native marine species have been detected within the region. The black scar oyster (Magallana bilineata) has been found in several locations including Mission Beach, Mourilyan Harbour, Cairns, Port Douglas, Cooktown, and Elim Beach, representing the first record of this species in Australia. Its invasive potential is still being evaluated. The Asian green mussel (Perna viridis) has also been intercepted in the region, including incursions in Escape River (2019) and Cairns (2021), and on multiple transiting vessels; however, no established wild populations are currently confirmed (DAF, 2024).

Pathways for marine pest introductions include hull biofouling, internal seawater inlets, movement of aquaculture stock and equipment, and larval transport via ballast water. Managing these pathways is widely recognised as the most effective strategy for minimising biological invasions in marine environments, where eradication and control efforts have often proven unsuccessful (Hayes & Sliwa, 2003; Bax et al., 2003; GBRMPA, 2024).

To address these risks, GBRMPA collaborates with federal and state biosecurity agencies under the National System for the Prevention and Management of Marine Pest Incursions. Key measures include the designation of most Queensland ports as First Points of Entry under the Biosecurity Act 2015, requiring risk-based inspections and compliance with antifouling and ballast water regulations; Implementation of the Queensland Seaports eDNA Surveillance (Q‑SEAS) program, a nationally recognised early detection initiative using molecular techniques to monitor for invasive marine species; Alignment with national response planning frameworks, including the Marine Pest Plan 2018–2023 and coordination through the Marine Pest Sectoral Committee.