Many of the key processes of the Great Barrier Reef ecosystem are changing and this is negatively affecting the health of the ecosystem.

Increased sedimentation and inputs of nutrients and pesticides to the ecosystem are affecting inshore areas, causing algal blooms and pollutants to accumulate in sediments and marine species, reducing light and smothering corals. Sea temperatures are increasing because of climate change, leading to mass bleaching of corals, and increasing ocean acidity is affecting rates of calcification. These processes combined are essential to the fundamental ecological processes of primary production and building coral reef habitats on the Great Barrier Reef.

It is considered that the overall food web of the Great Barrier Reef is being affected by declines in herbivory in inshore habitats because the urban coast dugong population is a fraction of its former population; in predation on reef habitats because of potential reef-wide differences in coral trout and shark numbers on reefs open and closed to fishing; and in particle feeding on reef habitats because of the reduction in at least one species of sea cucumber.

Combined with more frequent outbreaks of disease and pests and changes in other physical, chemical and ecological processes, declines in these processes mean that the health of the Great Barrier Reef ecosystem is reduced.

Current state and trends of physical processes

The physical processes of the Great Barrier Reef are changing, in particular sedimentation and sea temperature. Further changes in factors such as sea temperature, sea level and sedimentation are expected because of climate change and catchment runoff.

• Ocean currents
• Cyclones and wind
• Freshwater inflow
• Sedimentation
• Sea level
• Sea temperature
• Light

Current state and trends of chemical processes

For much of the Great Barrier Reef, the chemical environment has deteriorated significantly, especially inshore close to developed areas. This trend is expected to continue. Acidification of all Great Barrier Reef waters as a result of increased concentrations of atmospheric carbon dioxide is an emerging serious issue which is likely to worsen in the future.

• Nutrient cycling
• Pesticide accumulation
• Ocean acidity
• Ocean salinity

Current state and trends of ecological processes

Most ecological processes remain intact and healthy on the Great Barrier Reef, but further declines in physical and chemical processes are expected to affect them in the future. There is concern for predation, as predators are much reduced in many areas. Populations of large herbivores (such as dugongs) are severely reduced, however populations of herbivorous fish remain intact.

• Microbial processes
• Particle feeding
• Primary production
• Herbivory
• Predation
• Symbiosis
• Reef building
• Competition
• Connectivity

Current state and trends of outbreaks of disease, introduced species and pest species

Outbreaks of diseases appear to be becoming more frequent and more serious on the Great Barrier Reef. Outbreaks of pest species appear to be above natural levels in some areas.

• Outbreaks of diseases appear to be becoming more frequent and more serious on the Great Barrier Reef. Outbreaks of pest species appear to be above natural levels in some areas.
• Outbreaks of disease
• Outbreaks of crown-of-thorns starfish
• Introduced species
• Other outbreaks