How healthy is the Great Barrier Reef?

If the Great Barrier Reef was a person, doctors would describe it as a patient with serious chronic conditions that have to be closely monitored and managed. It wouldn’t yet be in intensive care, but hospital reports would certainly describe its condition as serious and multiple treatments would be administered to assist with recovery.

The analogy between a coastal/marine ecosystem and a human body can be appropriate when talking about their ‘health’ because both are complex, dynamic systems in which the overall picture is the sum of many parts.

We can describe a person as ’not doing well’ or ’pretty good considering’, but that glosses over the specifics of, say, strong bones but a weak heart, or that a number of problems might be linked back to a poor diet or a childhood illness.

The same could be said about the Great Barrier Reef. While the overarching scientific consensus is that the Reef’s ecosystems continue to be in poor condition, to understand why – and what that means – we need to look at the various parts. You can think of the different ecological components of the Reef as different organs that play different roles, and the different regions of the Reef as different parts of the body.

The overall health of a reef is determined by the state of – and pressures on – its water quality, wetlands, estuarine ecosystems and seagrasses, as well as its coral and other species.

Studies show that the quality of sea water in inshore areas of the Reef is in moderate to poor condition, largely because increased land run-off, made worse during floods, carries sediments and pollutants with it. Examining coral cores has revealed how this run-off has increased since the start of European settlement, and we now know that nutrients, sediment and pesticides are in the Reef’s waters all year round.

Inshore seagrass meadows are also affected by these contaminants, leaving them vulnerable to stresses such as reduced light. Along the Reef, seagrass is considered to be in poor condition, despite being more abundant in some areas. Of concern is poor reproductive effort, indicating a low capacity to recover from disturbances.

Mangroves and saltmarshes also continue to be affected by excess nutrients, sediment and pesticide loads, especially during periods of high rainfall, with damage due to tropical storms noted in some areas.

Excess nutrients, as observed after significant flood events, are also believed to be one of the main factors behind outbreaks of coral-eating crown-of-thorns starfish, which can devastate the Reef.

Overall, the condition of many coastal freshwater wetlands continues to be affected by all of these factors, as well as things such as changing water quality and invasive species. Wetlands are critical in supporting the healthy functioning of the Reef. They can improve water quality by filtering out land-based pollutants, but they are, in turn, negatively affected by those pollutants.

And what about coral?  Extensive bleaching in 2016 caused significant coral mortality, particularly north of Port Douglas, yet a number of inshore reefs escaped major damage. Severe coral bleaching affected the central third of the Great Barrier Reef in early 2017 associated with unusually warm sea surface temperatures and accumulated heat stress.

While coral cover has declined in the Cairns–Cooktown area in recent years because of cyclones and crown-of-thorns starfish, hard coral cover in areas south of Cairns has increased during a period of low disturbance. Similarly, mid-shelf and outer-shelf reefs in the southern half of the Reef have shown ability to recover.

This highlights two important things. The health of such a large Reef will always vary from place to place at different times, and it will always be affected by natural phenomena such as cyclones and tropical storms, which then have flow-on effects.

When we look at how the Great Barrier Reef is faring as a whole – given its size - we need to think in terms of its resilience: how well equipped is it to recover from climatic disruptions when they inevitably come? Just as people find it easier to fight through an annual dose of the flu if they are otherwise fit and healthy – in simple terms – the Reef is better able to bounce back from a cyclone if it’s not under stress in other ways. Improvements in water quality can significantly help reefs recover faster.

Unfortunately, the Reef is under greater and more constant stress from factors such as climate change, land run-off and coastal development. Increasing sea temperatures, as a result of climate change, are the highest and most immediate risk for the Reef. Sea surface temperatures of the Great Barrier Reef have increased by 0.8°C (on average) since the late 19th century and will continue to rise. Climate records highlight the unusual nature of this recent warmth and also provide evidence of more frequent extreme rainfall and river flows.

Scientists are continually monitoring the Reef’s ’vital signs’.

A new monitoring and evaluation program, the Reef 2050 Integrated Monitoring and Reporting Program (RIMReP), is being developed to provide a comprehensive understanding of how the Reef 2050 Plan is progressing. The program will include information about ecosystem health, biodiversity, water quality, heritage, community benefits, economic benefits and governance — the seven themes that make up the Reef 2050 Plan.

A key monitoring and modelling component to be integrated into RIMReP is the Paddock to Reef program. It was established in 2009 to provide data on management practices, catchment indicators, catchment loads and the health of the Reef across a range of scales.

These programs will help determine the best response to the Reef’s health needs, and the right mix of prevention and treatment.

Last updated
13 February 2019