The natural context of changes in the Great Barrier Reef - The Great Barrier Reef: An Environmental History - page 38

impacts of terrigenous sediment deposition on coral reefs have been exacerbated
by high water velocities: this is because high rates of sediment accumulation have
coincided roughly with the effective wave zone, which has caused re-suspension
of the sediments, representing a natural process of deteriorating water quality
over the last 6,000 years (Hopley, 1994). Again, a geomorphological perspective
suggests that caution is required in interpreting the deterioration of nearshore
coral reefs in the Great Barrier Reef: it is not possible to attribute that deterioration
solely to anthropogenic influences, as there are also geomorphological reasons
for the decline in water quality in the region. Indeed, from a geomorphological
perspective, the deterioration of the nearshore coral reefs of the Great Barrier
Reef is almost inevitable, since the control exerted by sea level no longer allows
juvenile reefs to form.
This morphogenic perspective provides a natural, large-scale context for the
accounts of historical changes in the Great Barrier Reef that follow. Those recent
changes should be interpreted against a background of the high vulnerability of
fringing and nearshore regions reefs as a result of their Holocene evolution. The
anthropogenic activities that are described in subsequent chapters - including
coral mining and coral collecting - have affected some coral reefs that already
had limited capacity to recover from environmental stresses. In some cases,
the impacts of those activities probably caused the complete mortality of
parts of some reefs; the degradation of the reefs at Goold Island, Kings Reef
and Alexandra Reef may have occurred in this way. Yet some anomalies
exist in this framework: Middle Reef, near Townsville, for instance, appears
to display an unusual degree of resistance to mortality, despite experiencing
highly turbid water conditions; on that reef, one oral history informant stated,
an 'absolutely amazing amount of coral' was foun d. 1 The reefs of Halifax Bay,
similarly, contain some apparently resilient reefs, possibly as a result of their
more stable foundations on Pleistocene gravels. Nevertheless, this model of
geomorphological controls on the Holocene evolution of the Great Barrier
Reef provides a valuable means of interpreting the impacts of human activities
and changes in vulnerable coral reefs.
Tropical cyclone damage to coral reefs
During the Holocene evolution of the Great Barrier Reef, coral reefs have also
experienced geomorphological changes due to tropical cyclone-related wave
action, including abrasion as coral fragments and other debris are thrown against
coral colonies. The patterns of occurrence and severity of tropical cyclones in the
Great Barrier Reef have been reconstructed by several authors. Puotinen et al.
(1997) documented the historical frequency and paths of some cyclones in the
Great Barrier Reef, demonstrating the recurrent nature of those storms in the
region. Nott and Hayne (2001) and Nott (2003) have reconstructed the severity
of tropical cyclones in the region, showing that some of those storms could
be exceptionally destructive. Tropical cyclones, therefore, represent another