Introduction - The Great Barrier Reef: An Environmental History - page 5

The decline of the Great Barrier Reef
Concerns about the condition of the Great Barrier Reef (and of other coral reefs
worldwide) increasingly focus on the global-scale threats to these ecosystems
presented by climate change, especially the effects of coral bleaching, ocean
acidification and sea-level rise. Such concerns are acute since it is now recognised
that, under conditions expected to occur in the twenty-first century, global
warming and ocean acidification will compromise the ability of corals to form
robust carbonate skeletons, with the result that coral reef ecosystems are expected
to become less diverse and to have reduced capacity to maintain carbonate reef
structures (Hoegh-Guldberg et al., 2007, p1737). In addition, those broad-scale
changes are likely to interact synergistically with other impacts, exacerbating
the effects of water pollution and disease, and thereby forcing coral reefs closer
towards thresholds for functional collapse. Consequently, rapid climate change in
conjunction with a range of other impacts is expected to lead to the widespread
degradation and destruction of corals and coral reefs worldwide, with serious
implications for tourism, reef-associated fisheries, coastal protection and human
communities dependent upon reef resources (Hoegh-Guldberg, 1999; Lough,
1999; Hoegh-Guldberg et al., 2007; Veron, 2009). Within that broader context,
the resilience of coral reef ecosystems to the effects of climate change could be
enhanced if other (regional and local) environmental stresses are minimised.
From this perspective, it becomes important to characterise and understand the
extent to which the Great Barrier Reef is - and has already been - affected by
those other environmental stresses, including historical ones.
Although the current, global-scale threats to coral reef ecosystems - especially
those due to climate change - are formidable ones, the deterioration of coral reefs
may have commenced much earlier than those threats were first recognised. Many
reports suggest that the condition of the Great Barrier Reef has declined since
European settlement commenced in Queensland, as a result of direct exploitation
and the development of adjacent coastal land. In particular, the terrestrial runoff
of sediments, nutrients and other pollutants has probably caused a substantial
deterioration of water quality in parts of the Great Barrier Reef, and those
effects - together with the over-exploitation of reef resources - have significantly
degraded some nearshore coral reefs and seagrass communities. The Queensland
Environmental Protection Agency (QEPA, 1999, p5.4) reported that nutrient
inputs to the Great Barrier Reef lagoon have increased substantially over the
decadal timescale due to extensive land clearing, catchment development and
coastal runoff, and that the relatively enclosed and shallow nature of the lagoon
makes it relatively susceptible to the effects of eutrophication and deteriorating
water quality. Williams (2001, pp3-4) argued that sediment discharges
have increased by three or four times, nitrogen discharges have doubled and
phosphorus quantities have increased by six to ten times since 1800; as a result,
the impacts of terrestrial runoff of nutrients and sediments on coastal parts of the
GBRWHA - due to both past and current land use practices - have become a