Thanks largely to the accumulated knowledge of basic and strategic research, ranging from the Great Barrier Reef Expedition of 1928 to the present, applied scientists and managers now take a lot for granted about the nature and function of the Great Barrier Reef.

Examples of contributions

When the author began to work on coral reefs in the mid-1970s, coral reefs were generally assumed to be very fragile and very stable. With little more than US ecology text books to go on, it was widely assumed that a supposedly benign tropical environment and the high species diversity of coral reefs would combine to dampen out major fluctuations in the abundance of the corals, fish and other creatures which live on reefs. With such background stability, it would be easy to distinguish human-induced instability from nature's balance. There are indeed parts of coral reefs - very sheltered areas in particular - where those concepts do sum up the situation very well.

However, it is misleading to suppose that the concepts apply to all parts of all reefs. For a manager asked to 'do some-thing' because a reef has degraded, there is a need to be reasonably sure the degradation is not natural. Some of the research findings relevant to this issue relate to variability in space and time.

In terms of spatial variability, seventeen different types of 'coral community' have been identified on reefs at different distances from land, and across depth zones and reef-tops within individual reefs⁵. Like vegetation types across a landscape, the abundance of different plants and animals in these communities varies according to many factors: wave energy and turbidity; the types and numbers of fish and other grazing organisms; the ecological succession, and the history of disturbance; the quality of the water flowing onto the reefs⁶.

As regards temporal variability, GBR coral reefs are periodically disturbed by events like cyclone waves, floods and crown-of-thorns starfish.

• Cyclones and floods are directly generated by global weather systems and their frequency and severity are greatest in anti-El Nino years⁷.These events also affect ocean productivity and other aspects of the ecosystem function, possibly including the generation of crown-of-thorns outbreaks.
• It is also plausible that the frequency and severity of floods and outbreaks of crown-of-thorns starfish may have been changed by humans: by damming and land and water use in the case of floods, and by unknown factors affecting survival of one or more stages of the starfish's life cycle.
• Shallow monitored sites on reefs which had had their entire perimeters badly damaged by crown-of-thorns starfish became picture post-card beautiful' in around a decade, whereas deeper and sheltered sites have often been slow to even begin recovery, due to either poor supply of coral larvae, poor survival, or both (Figures 2a and 2b).
• Concerns about losses among the slower growing components of the coral community are underscored by data suggesting that the recently observed 15-year interval between outbreaks may only be sustainable at some locations. At others, it would lead to fairly rapid reduction and eventual loss of all the impressive ancient colonies - like a forest without its ancient trees (Figure 2c).
• On the Great Barrier Reef, unlike reefs in calmer equatorial latitudes, wholesale destruction of large areas of corals by cyclone-generated waves is a normal occurrence¹⁰. Calculation suggests that a coral that would have a 50% chance of reaching 60 years of age at Lizard Island (latitude 16°S) would have only a 10% chance if it had happened to settle instead on a reef off Mackay (latitude 2I°S).

The destructive influence of cyclones on coral reefs is very patchy due to sheltering effects and differences in the vulnerability of different coral community types and ages.

The other 70% - diverse shapes and ages of a few years to a few decades - are highly vulnerable and apparently disturbed by cyclones, in a very patchy manner, every few decades.

With such wide ranging background variability, managers asked to 'do some-thing' in response to reports of change in coral reefs must first make some difficult assessments: whether or not human influence has prematurely initiated an otherwise 'normal' change; or whether or not human influence has caused an abnormal change. They may, for example, institute some form of management or mitigation of human influence (for example in terms of anchoring, divers, land or sea-based pollution, over-fishing, destructive fishing, collecting or harvesting).

Long-term monitoring of GBR coral reefs indicates that it is not reasonable to expect coral reefs to be 'picture-post-card beautiful' in all places at all times, but monitoring alone cannot answer the questions: 'Can this reef state be considered satisfactory at this place and time?' and, for large sections of the GBR, 'How many reefs in various states and stages of recovery are expected?' These questions require an understanding of reef ecology and environment based on ongoing multi-disciplinary research.