Geoscience Reference
In-Depth Information
Table 3.1 Main types of coral reef classified by geomorphological characteristics
Type of reef
Characteristics of reef
Examples
Severely
impacted reefs
Reefs influenced by a nearshore mud-silt
wedge
Conditions of continuous turbidity
Mortality of corals with little or no
recovery
Complete collapse of reef ecosystems
Stone Island reef
Goold Island reef
Alexandra Reef
Significantly
impacted reefs
Patchy reefs
High variability in coral mortality and
recovery
Ecological change in coral reef ecosystems
Selection of sediment-resistant species
Survival of impact-resistant forms of coral
Increased prevalence of soft corals
Palm Island reefs
Halifax Bay reefs
Middle Island reefs
Cape Tribulation reefs
Moderately
impacted reefs
Mid-shelf reefs with limited terrestrial
influence
High cover of living corals
Recovery of corals from severe impacts
Increased coral skeleton porosity
Increased bioerosion of corals
Holbourne Island reef
Slightly impacted
reefs
Offshore reefs with slight terrestrial
influence
Healthy, resilient corals
Terrestrial influence not visible
Geochemical analysis required to reveal
impacts
Wallaby Reef
Kangaroo Reef
Source: Based on information provided by D. Hopley, personal communication, 20 October 2003
be much harder for the recovery of reefs to take place; in other words, it may
now be much easier to 'turn-off' than to 'turn-on' coral growth in many parts
of the Great Barrier Reef. Moreover, this approach suggests that, once a coral
reef is established, it may withstand fairly poor environmental conditions; but,
once a critical ecological threshold is crossed and a phase shift occurs, then the
quality of those conditions may need to be improved significantly for recovery of
that reef to occur. The degradation of parts of the Great Barrier Reef - for both
natural and anthropogenic reasons - therefore increases the vulnerability of the
ecosystem to other disturbances, even the effects of single events such as tropical
cyclones or floods.
The deterioration of the coral reefs within 20 or 25 kilometres of the
Queensland coast, therefore, has probably occurred as the impacts of sediment
and nutrient run-off from the mainland have accelerated the natural tendency
of those reefs to reach a stage of geomorphological senility (Hopley, 1994). The
naturally-occurring mud-silt wedge, which may extend for several kilometres
offshore, encroaches on some nearshore reefs (as in Halifax Bay) and also on
the fringing reefs of some nearshore continental islands. In those locations, the
 
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