GREAT BARRIER REEF
// Outlook Report 2014
Healthy connections between marine and freshwater habitats are important to the Reef ecosystem
© Matt Curnock
3.7.6 Overall summary of ecosystem health
The past decade of extreme weather events, combined with the continuing poor condition of key processes such as sedimentation and nutrient cycling, have caused the overall health of the Great Barrier Reef ecosystem to deteriorate since 2009. While improved land management practices are beginning to reduce the amount of nutrients and sediments leaving the catchment, there is likely to be a long lag time between these improvements and reductions in pollutants flowing into the Region, and again between that and improvements in related marine processes. The decline in ecosystem health is most pronounced in inshore areas of the southern two-thirds of the Region. In contrast, the continuing good and very good condition of almost all processes in the northern third of the Region and in offshore areas means that the ecosystem in these areas continues to be healthy. Ecosystem processes are integral to the attributes recognised in the world heritage listing of the Great Barrier Reef. The deteriorating condition of many is likely to be affecting its outstanding universal value. One indicator of declining ecosystem health is that crown-of-thorns starfish outbreaks are becoming more frequent. Rather than experiencing outbreaks in a natural cycle of about every 50 to 80 years, the Reef has been affected by three in the past 50 years and a new outbreak has begun. Crown-of-thorns starfish have been a major cause of coral loss in recent decades. There is growing evidence of a link between outbreaks and deterioration in the process of nutrient cycling. The overall grade of ‘good’ for outbreaks of disease, introduced species and pest species is borderline with ‘poor’ due to the severity of crown-of-thorns starfish outbreaks in recent years. Sea temperature is increasing. While other environmental conditions (for example cloud cover and wind) have meant periods of elevated temperature have not been as prolonged as those in the late 1990s and early 2000s, the trend of increasing temperatures places the ecosystem at serious risk into the future. Other processes likely to have a Reef-wide influence on ecosystem health, such as ocean pH and sea level, are also expected to deteriorate into the future. Terrestrial habitats that support the Great Barrier Reef ecosystem are generally in very good condition north of Port Douglas. Further south, in the bulk of the Region’s catchment, all supporting habitats have been substantially modified. This has affected connectivity and the capacity for these habitats to support marine habitats and species. Knowledge of the key variables that contribute to some physical and chemical processes — such as sedimentation, sea temperature, nutrient cycling and freshwater inflow — is improving. There remains a poor understanding and almost no monitoring of many others, especially ecological processes such as connectivity, competition, predation and microbial processes. Monitoring pest introductions remains a gap.