GREAT BARRIER REEF
// Outlook Report 2014
Outlook report 2009: Overall summary of ecosystem health
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 in 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.
As outlined in the Great Barrier Reef Outlook Report 20091, the notion of ‘health’ can be applied to both individual organisms and an ecosystem as a whole. An ecosystem is considered healthy if it is able to maintain its structure and function in the face of external pressures.2 In order to systematically assess the health of the Great Barrier Reef ecosystem, its main physical, chemical and ecological processes are considered (Figure 3.1).
Figure 3.1 Major physical, chemical and ecological processes
The health of the Great Barrier Reef ecosystem is assessed by considering its physical, chemical and ecological processes as well as the condition of its supporting terrestrial habitats. Outbreaks of pests and diseases are also considered as a guide to overall health.