Australia
currents are reversed with a weak southward flowing
current in the north, but stronger in more southerly
latitudes. These patterns of current flow are altered by
patterns of tidal flow, particularly in the areas of more
complex reef networks, but there remains a predominant
pattern of water movements along the continental shelf,
with little cross-shelf movement.
Although best seen as a continuous reef complex, it
is possible to distinguish a number of ecological regions
within the Great Barrier Reef.
Torres Strait
In the far north of Australia the continental shelf forms a
wide connecting platform across the Torres Strait to Papua
New Guinea. As most of the islands in the Torres Strait
fall under Australian jurisdiction so do the reefs and
waters of the Strait. There is considerable freshwater and
sediment input from the Papua New Guinea coastline,
however there are several very extensive platform reefs
across the relatively shallow waters of the Strait. The
westernmost areas have the shallowest and most turbid
waters. A large chain of reefs runs between Prince of
Wales Island and Moa Island. Like other reefs in the area,
these show a very clear east-west alignment associated
with the high velocity tidal currents running through the
area. The Warrior Reefs further to the north and east run
in a chain towards the coastal town of Daru in Papua New
Guinea. Sediment loads are high in this area, and much of
the shallow surface of these reefs is dominated by soft
muds, although they are fringed by coral on their eastern
margins. Finally there is a wide area of platform reefs
around Darnley Island, stretching out towards the edge of
the continental shelf and the near continuous line of reefs
which mark the northern edge of the outer barrier reef.
Northern section
Due east of Cape York the continental shelf remains wide,
but it then narrows rapidly towards Raine Island and continues as a platform typically less than 50 kilometers wide.
The most distinctive feature of this sector of the Great
Barrier Reef is the well developed ribbon-type barrier reefs
on the outer edge: long narrow ribbon reefs typically less
than 500 meters wide but extending up to 25 kilometers
in length and separated by relatively narrow passes. They
are located right on the edge of the continental shelf,
and depths drop rapidly to over 1 000 meters only a few
hundred meters from the eastern edges of some reefs. For
about 80 kilometers, in the northernmost sector of these
ribbon reefs, there are spectacular deltaic formations in the
channels between the reefs. Rather like river deltas, these
have been formed in the calmer waters behind the reef
by the deposition of sediments from the powerful currents
which flow between the reefs. The banks of sediments have
then formed a substrate for new reef development.
Inshore of the ribbon reefs there are well developed
mid-shelf and inner shelf reefs, while there are also
wide areas of submerged //a/imei/a-dominated shoals
and banks. This is one of the only areas where there are
fringing reefs directly adjacent to the mainland coast,
although coral cover and diversity are limited. Raine
Island just off the continental shelf has the largest nesting
populations of green turtles in the world as well as some
of the most important seabird rookeries. There are only
a few high islands on the continental shelf, notably the
Flinders group and Lizard Island. These have important
and extensive fringing reefs.
Central section
This section extends from Mossman in the north to the
barrier reef offshore from the Whitsunday and Lindeman
Islands. Over this area the continental shelf gradually
widens, with reef development largely restricted to its
outer third. Closer to the mainland the waters are subject
to considerable fluctuations in turbidity and salinity due
to the seasonal flooding of rivers. The reefs in this area
are younger than those to the north. Many have lower and
less extensive reef flats, and coral cays are largely absent,
while their outer reef crests are often only clearly developed on the windward southeastern margins. Overall the
reefs are less tightly packed and hence do not form such a
continuous barrier The main reefs are also set back a little
from the true edge of the continental shelf, although there
are several reefal shoals close to the outer shelf margin
which rise to within 10 meters or so of the surface and
have active coral growth. Over relatively short geological
timescales these could evolve into ribbon reef systems
similar to those observed to the north. In addition to the
barrier reef structures there are important fringing reef
communities associated with a number of high island
groups, notably the Palm Islands and the Whitsunday and
Lindeman Islands to the south.
The Swain and Pompey
Connplexes
This is the sector of the Great Barrier Reef where the
continental shelf is at its widest and the main reefs are
furthest from shore. The Pompey Complex has a number
of submerged reefs on the edge of the continental shelf.
However, about 10 kilometers back from this edge is a
vast and complex array of very large reef platforms
separated by countless meandering channels making a
nearly solid mass of reefs nearly 200 kilometers in length
and up to 20 kilometers wide. The high tidal range in this
area drives strong currents reaching up to 10 knots, which
currents are reversed with a weak southward flowing
current in the north, but stronger in more southerly
latitudes. These patterns of current flow are altered by
patterns of tidal flow, particularly in the areas of more
complex reef networks, but there remains a predominant
pattern of water movements along the continental shelf,
with little cross-shelf movement.
Although best seen as a continuous reef complex, it
is possible to distinguish a number of ecological regions
within the Great Barrier Reef.
Torres Strait
In the far north of Australia the continental shelf forms a
wide connecting platform across the Torres Strait to Papua
New Guinea. As most of the islands in the Torres Strait
fall under Australian jurisdiction so do the reefs and
waters of the Strait. There is considerable freshwater and
sediment input from the Papua New Guinea coastline,
however there are several very extensive platform reefs
across the relatively shallow waters of the Strait. The
westernmost areas have the shallowest and most turbid
waters. A large chain of reefs runs between Prince of
Wales Island and Moa Island. Like other reefs in the area,
these show a very clear east-west alignment associated
with the high velocity tidal currents running through the
area. The Warrior Reefs further to the north and east run
in a chain towards the coastal town of Daru in Papua New
Guinea. Sediment loads are high in this area, and much of
the shallow surface of these reefs is dominated by soft
muds, although they are fringed by coral on their eastern
margins. Finally there is a wide area of platform reefs
around Darnley Island, stretching out towards the edge of
the continental shelf and the near continuous line of reefs
which mark the northern edge of the outer barrier reef.
Northern section
Due east of Cape York the continental shelf remains wide,
but it then narrows rapidly towards Raine Island and continues as a platform typically less than 50 kilometers wide.
The most distinctive feature of this sector of the Great
Barrier Reef is the well developed ribbon-type barrier reefs
on the outer edge: long narrow ribbon reefs typically less
than 500 meters wide but extending up to 25 kilometers
in length and separated by relatively narrow passes. They
are located right on the edge of the continental shelf,
and depths drop rapidly to over 1 000 meters only a few
hundred meters from the eastern edges of some reefs. For
about 80 kilometers, in the northernmost sector of these
ribbon reefs, there are spectacular deltaic formations in the
channels between the reefs. Rather like river deltas, these
have been formed in the calmer waters behind the reef
by the deposition of sediments from the powerful currents
which flow between the reefs. The banks of sediments have
then formed a substrate for new reef development.
Inshore of the ribbon reefs there are well developed
mid-shelf and inner shelf reefs, while there are also
wide areas of submerged //a/imei/a-dominated shoals
and banks. This is one of the only areas where there are
fringing reefs directly adjacent to the mainland coast,
although coral cover and diversity are limited. Raine
Island just off the continental shelf has the largest nesting
populations of green turtles in the world as well as some
of the most important seabird rookeries. There are only
a few high islands on the continental shelf, notably the
Flinders group and Lizard Island. These have important
and extensive fringing reefs.
Central section
This section extends from Mossman in the north to the
barrier reef offshore from the Whitsunday and Lindeman
Islands. Over this area the continental shelf gradually
widens, with reef development largely restricted to its
outer third. Closer to the mainland the waters are subject
to considerable fluctuations in turbidity and salinity due
to the seasonal flooding of rivers. The reefs in this area
are younger than those to the north. Many have lower and
less extensive reef flats, and coral cays are largely absent,
while their outer reef crests are often only clearly developed on the windward southeastern margins. Overall the
reefs are less tightly packed and hence do not form such a
continuous barrier The main reefs are also set back a little
from the true edge of the continental shelf, although there
are several reefal shoals close to the outer shelf margin
which rise to within 10 meters or so of the surface and
have active coral growth. Over relatively short geological
timescales these could evolve into ribbon reef systems
similar to those observed to the north. In addition to the
barrier reef structures there are important fringing reef
communities associated with a number of high island
groups, notably the Palm Islands and the Whitsunday and
Lindeman Islands to the south.
The Swain and Pompey
Connplexes
This is the sector of the Great Barrier Reef where the
continental shelf is at its widest and the main reefs are
furthest from shore. The Pompey Complex has a number
of submerged reefs on the edge of the continental shelf.
However, about 10 kilometers back from this edge is a
vast and complex array of very large reef platforms
separated by countless meandering channels making a
nearly solid mass of reefs nearly 200 kilometers in length
and up to 20 kilometers wide. The high tidal range in this
area drives strong currents reaching up to 10 knots, which