Scales of Structures, Scales of Processes: The Great Barrier Reef, Australia
From RAWorkbook
The Great Barrier Reef provides an example of how to identify cross-scale structures and processes that influence resilience. Running 2000 km along the northeast coast of Australia the GBR is the largest coral reef system in the world, covering an area of about 350,000 km2. The reef system is comprised of about 3,000 individual reefs, and is structured and influenced by processes that occur across a range of scales- from seconds to millennia in time and from fractions of meters to the globe. Human-mediated processes also span multiple scales, from harvesting individual organisms such as sea cucumbers, snails, and fish, to regional-scale land use that alters nutrient and sediment inputs, to global warming that raises ocean temperatures and causes coral bleaching.
Ecosystem Scales
The reef structures shown across these scales are subjected to broader-scale processes and disturbance. Tropical cyclones, tsunamis, crown of thorn outbreaks, and warming events occur at scales of thousands of kilometers. Yet following these disturbances, other factors, such as over-fishing, climate change, or disease can eliminate local larvae sources, thereby limiting the ability of reefs to recover at local scales. Without larval sources these reefs can undergo phase shifts to an algae-dominated state. Species with larger dispersal ranges can re-colonize areas where local larval sources no longer exist. For this reason, maintaining connections between reefs that accommodate how far species are able to disperse, contributes to a system’s resilience.
Degradation of a number of small reef patches can lead to larger-scale collapse. When a reef flips to an algal-dominated state, it can no longer supply larvae to surrounding areas. As subsequent disturbances occur, with fewer larval sources, more reefs shift to algae-covered rubble. A cascade of such phase shifts can dramatically increase the size of the altered area.
Scales of Humans and Management
Other impacts on the system such as fishing, may be felt locally yet can be driven by processes happening at a variety of scales and across multiple domains (e.g., social, economic, and ecological). In the case of fishing, complex interactions involving fish stocks, ease of access, market demands, and rules and regulations, among others, may be all influenced by processes and dynamics at local, regional and global scales.
Reef-wide concern over the impacts of drilling and mining led to the establishment of the Great Barrier Reef Marine Park Authority in the mid 1970s. This federal funded institution focused on restricting activity throughout the entire reef area. Over the past three decades a multi-scale management structure has developed that links local advisory groups with state and federal agencies. The Park authority had assumed that the sheer size of the entire barrier reef would be resilient in the face of any of the disturbances.
However, by the late 1990s, spurred in part by reports of large-scale reef collapses in the Caribbean Sea, scientists became concerned that an increase in bleaching events (and other unknown effects of climate change), as well as increased fishing pressure would make the reefs in the GBR more vulnerable to a loss of resilience. Using new analyses of long-term monitoring data, and the above arguments, managers went to parliament to change the scales of management. Parliament acted, which resulted in rezoning the entire GBR and a net increase in protected areas.
