Interpreting the data: Spatial and temporal variability
Interpreting the data: Spatial and temporal variability
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| The variability and complexity of coral reefs makes it very difficult for scientists to detect and identify clear declines in coral reef condition that is attributable to human influences. However, subtle signs of reef dysfunction are now apparent on some inshore reefs |
The spatial and temporal variability of coral reefs makes it very difficult to identify a decline in coral reef condition that is clearly attributable to human activities. These long-term studies have shown that even in the absence of direct human impacts, coral cover, growth and degradation vary considerably over time. To date, these studies have not indicated a clear, overall reef wide decline in coral condition with increasing settlement and human influence in the region. Nevertheless, this is neither unexpected nor a cause for complacency as explained below:
- Given the natural variability of coral reef ecosystems and the lack of data predating European settlement, clear signals of reef decline would most likely appear only after many more years of survey data was collected.
- Readily observable symptoms of stress can lag far behind the onset of ecosystem dysfunction. As such, conclusive evidence of a decline may only be found after major and potentially irreversible impacts have occurred, by which time it may be too late to initiate a response to alleviate the pressures causing the decline.
- Declines in reef condition are likely to be patchy, occurring only in some areas and at certain times. The high cost of monitoring programs means that existing studies are capable of detecting only relatively large and uniform changes in coral reef condition and are not designed to detect these types of subtle, patchy declines.
- Pressures on reef condition are likely to affect the biological and ecological functions of the reef (for example, the ability to recover from disturbances), and would occur before clear trends in coral cover appeared. There are no long-term studies that explicitly monitor the condition of these ecological functions, and even if such data were available, our ability to interpret this information is limited by our incomplete understanding of these processes.
There is also considerable evidence suggesting that degradation of ecological processes on inshore reefs has occurred. Surveys on some inshore reefs have indicated that recovery from crown-of-thorns starfish outbreaks is taking longer than previously recorded, while other surveys have reported altered community composition and reduced recruitment success. Surveys have also shown that coral cover on inshore reefs adjacent to heavily modified catchments is lower than expected based on comparisons between inshore and offshore reefs in relatively pristine areas. While it cannot be proven that these observations are attributable to human activities, they indicate that the ecological capacity of these reefs to recover and reproduce is declining. Furthermore, these are the changes most likely to occur as a result of chronic, excessive pressure on coral reef ecosystems caused by human activities. Current studies into these issues are limited in both geographical and temporal scales, however given the potential pressures these reefs are experiencing (see Pressure) these observations of ecological dysfunction are of increasing concern to reef managers.
Interpreting the data: Ecological complexity
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| The GBRMPA is taking action to reduce pressures on the Great Barrier Reef before widespread declines occur |
Another confounding factor concerns the nature of reef communities themselves. Coral reefs in different places and at different times are likely to support different coral communities, each with their own unique suite of ecological characteristics and mechanisms. As such, different reef communities (or even the same reef at two different times) may respond differently to similar environmental changes or disturbance events. For example, the susceptibility to cyclones and subsequent recovery rate of reefs dominated by fast growing Acroporid corals is much higher than that of reefs dominated by slow growing but more robust Porites corals. This ecological complexity makes it very difficult to accurately interpret long term monitoring data.
Current conditions assessment
- Clear pressures on the coral reefs of the Great Barrier Reef exist, many of which are known to have directly contributed to the degradation of coral reefs in other parts of the world (See Pressure).
- Considering the difficulties in detecting and identifying the subtle signs of human induced declines, the absence of a reef wide decline in the condition of coral reefs does not mean that coral reefs are not under pressure.
- Evidence suggests that some coral reefs in the Great Barrier Reef are experiencing increasingly unsustainable levels of stress that have caused subtle, localised declines in the condition of these reefs.
- The GBRMPA is taking action to reduce the pressures on the Great Barrier Reef in the short term to ensure that widespread declines in coral condition do not occur at a later stage (See Response).