51
6. Seabed Environments, Habitats
and Biological Assemblages
C. R. Pitcher, P. J. Doherty & T. J. Anderson
physical factors. Overlaid on the broad patterns, the
majority of variation in the biota results from a multitude of biological and stochastic processes.
N GEOPHYSICAL CONTEXT AND PROCESSES
Offshore from Townsville in the central GBR (about
18.2–19.2°S), where most previous studies have been
conducted, the continental shelf is about 120 km wide.
On the outer 40–50 km of the shelf, an open matrix of
coral reefs rises from 50–70 m depth. Between the coast
and the reef matrix, a 75 km wide stretch of water
known as the GBR Lagoon is almost devoid of reefs
possibly due to the action of frequent cyclones.
North of 18°S, the shelf narrows (to about 50 km
wide) and becomes shallower (typically 30 m, rarely
50 m). The outer shelf becomes delimited by a nearly
continuous barrier of ribbon-like reefs; with steep descents to the abyss beyond. Platform reefs are common,
often quite densely packed across the mid- and outershelf, and the GBR Lagoon becomes narrower (30 km
to 20 km).
South of 19°S, to 22°S, the shelf broadens to as much
as 250 km and generally becomes much deeper with
substantial areas 70 m. Two lines of hard-packed
reefs, the Pompeys, with narrow channels between,
The modern Great Barrier Reef rises from a shallow
(0–100 m) continental shelf of about 210 000 km², between the north-east Australian coast and the Coral
Sea. While shallow coral reefs are widely recognised as
an iconic habitat, they occupy only five percent of the
region. This chapter is about the diversity of benthic
habitats and biota of the deeper lagoon and inter-reefal
seabed areas of the remainder of the region.
Only a small fraction of this vast deeper seabed had
been examined by marine biologists during the 20th
century. Extensive new information was provided during 2003–2006 by the GBR Seabed Biodiversity Project,
which mapped the distribution of seabed habitats (including mud, sand and gravel flats; algae and seagrass
beds, sponge and gorgonian gardens, hard and shoal
grounds) and their associated biological diversity of
more than 7000 species, many new to science, across
the length and breadth of the GBR Marine Park.
The GBR seabed has alternated between terrestrial
and marine environments, due to repeated glacial periods over geological history (Chapters 2 and 3). Today’s seabed habitats and biodiversity still partly
reflect this history and are broadly influenced by
coastal processes (Chapter 11) on one side and oceanic
processes (Chapter 4) on the other, with numerous
subpatterns due to regional differences in several
6. Seabed Environments, Habitats
and Biological Assemblages
C. R. Pitcher, P. J. Doherty & T. J. Anderson
physical factors. Overlaid on the broad patterns, the
majority of variation in the biota results from a multitude of biological and stochastic processes.
N GEOPHYSICAL CONTEXT AND PROCESSES
Offshore from Townsville in the central GBR (about
18.2–19.2°S), where most previous studies have been
conducted, the continental shelf is about 120 km wide.
On the outer 40–50 km of the shelf, an open matrix of
coral reefs rises from 50–70 m depth. Between the coast
and the reef matrix, a 75 km wide stretch of water
known as the GBR Lagoon is almost devoid of reefs
possibly due to the action of frequent cyclones.
North of 18°S, the shelf narrows (to about 50 km
wide) and becomes shallower (typically 30 m, rarely
50 m). The outer shelf becomes delimited by a nearly
continuous barrier of ribbon-like reefs; with steep descents to the abyss beyond. Platform reefs are common,
often quite densely packed across the mid- and outershelf, and the GBR Lagoon becomes narrower (30 km
to 20 km).
South of 19°S, to 22°S, the shelf broadens to as much
as 250 km and generally becomes much deeper with
substantial areas 70 m. Two lines of hard-packed
reefs, the Pompeys, with narrow channels between,
The modern Great Barrier Reef rises from a shallow
(0–100 m) continental shelf of about 210 000 km², between the north-east Australian coast and the Coral
Sea. While shallow coral reefs are widely recognised as
an iconic habitat, they occupy only five percent of the
region. This chapter is about the diversity of benthic
habitats and biota of the deeper lagoon and inter-reefal
seabed areas of the remainder of the region.
Only a small fraction of this vast deeper seabed had
been examined by marine biologists during the 20th
century. Extensive new information was provided during 2003–2006 by the GBR Seabed Biodiversity Project,
which mapped the distribution of seabed habitats (including mud, sand and gravel flats; algae and seagrass
beds, sponge and gorgonian gardens, hard and shoal
grounds) and their associated biological diversity of
more than 7000 species, many new to science, across
the length and breadth of the GBR Marine Park.
The GBR seabed has alternated between terrestrial
and marine environments, due to repeated glacial periods over geological history (Chapters 2 and 3). Today’s seabed habitats and biodiversity still partly
reflect this history and are broadly influenced by
coastal processes (Chapter 11) on one side and oceanic
processes (Chapter 4) on the other, with numerous
subpatterns due to regional differences in several