The Great Barrier Reef
178
to the skeletons of modern hermatypic corals), as well
as discrete siliceous spicules within the soft tissues, virtually identical to those seen in their fossil ancestors
from the Lower Cretaceous (160 My) and Triassic
(250 My) respectively. Others have only a solid skeleton
composed of aragonitic crystals (a form of calcium carbonate) with no free spicules (e.g. Vaceletia crypta, with
a continuous fossil record from the Middle Triassic, 245
My, to present). Others have a solid skeleton of either
linked or rigid calcareous spicules (e.g. Plectroninia hindei, with a body plan known from the Mid Miocene, 23
My) or a rigid basal mass of calcite, and some (the socalled ‘ lithistids’) have only siliceous skeletons composed of special spicules called desmas, ranging from
entirely fused and forming a rock hard skeleton to
loosely articulated rendering the body more flexible
(e.g. Theonella swinhoei, with ancestors recorded from
the Tertiary, 65 My). These so-called ‘living fossil’
sponges are usually found in shaded or dark habitats,
such as in crevices, deep caves or under coral rubble,
rarely in full light, and due to their hard coralline texture may be confused with corals by the novice. Similarly, caves and dark crevices are also home to a variety
of soft-bodied demosponges, sometimes lacking pigments (e.g. Petrosia ( Stongyl-ophora) strongylata), sometimes colourful (e.g. Ulosa spongia), and especially the
multitude of frequently brightly coloured calcareous
sponges living on the reef (e.g. Leucetta chagosensis, Levinella prolifera and Soleniscus radovani) (Fig. 17.4C–H).
Reef slope
Between the reef crest and the base of coral reefs, across
the shelf of the GBR, occur large, predominantly heterotrophic sponges that feed on food particles and waste
products filtering down from the coral reef above. On
some reefs, particularly those closer to the coast, these
faunas number several hundred species, which in some
instances occur as large populations. Their morphologies are as diverse as the conditions they live under,
such as flexible whips, fingers and fans adapted for coping with high currents (Ianthella basta, Axos flabelliformis,
Clathria (Thalysias) cervicornis); soft tubes, vases and
other shapes that predominate in silty, turbid water
where inhalant and exhalant pores are located on different surfaces to prevent smothering (e.g. Echinochalina
(Protophlitaspongia) isaaci and Fascaplysinopsis reticulata),
and a number of ubiquitous, amorphous, bulbous, massive, spherical (and other shaped) forms that appear
nearly anywhere they can settle and survive (e.g. Cinachyrella schulzei, Stylissa massa, Stylissa carteri, Acanthella
cavernosa, Amphimedon terpenensis, Pericharax heterorhaphis, and Agelas axifera) (Figs 17.5A–H, 17.6A–H).
Deeper lagoon and inter-reef
Sponges living on the seabed in between the reefs are
generally very different to those found on the coral
reefs, living in high current, low light, turbid waters
where they burrow into soft sandy and muddy sediments (e.g. Oceanapia renieroides and Disyringia dissimilis), in seagrass and Halimeda beds (e.g. Oceanapia
sagittaria), or attached to hard objects on the sea floor
(e.g. Xestospongia testudinaria, Melophlus sarassinorum
and Liosina paradoxa) (Fig. 17.7A, C, G, H). Growth
forms include elongate species with root-like tufts or
bulbs for anchoring in soft sediments and long tubes to
prevent smothering, flexible fans and whips in high
current areas, and massive barrels and volcanoes attached to rock and coral outcrops. This fauna comprises
a significant proportion of the ‘benthos’, providing important habitat for other marine species, ranging from
aggregating fishes to numerous crustacean in-faunas.
In a recent major survey across the length and breadth
of the GBR, conducted under the auspices of the
Cooperative Research Centre for the GBR (CRC Reef),
approximately 1300 morphospecies of sponges
were discovered from the inter-reef region, which is
particularly susceptible to human impacts such as
trawling (see also Chapter 6). Whereas a number of
species living on the coral reef flats may be found on
both sides of the Australian continent, these deeper
water GBR lagoonal and inter-reef species appear to
differ significantly in composition from the fauna found
at similar latitudes on the west coast of the continent.
Reef bioeroders (sponges as ‘parasites’)
A special group of sponges are responsible for significant carbonate recycling on the reef, collectively termed
excavating (‘boring’ or bioeroding) sponges (see also
Chapter 8). They are responsible for extensive damage
178
to the skeletons of modern hermatypic corals), as well
as discrete siliceous spicules within the soft tissues, virtually identical to those seen in their fossil ancestors
from the Lower Cretaceous (160 My) and Triassic
(250 My) respectively. Others have only a solid skeleton
composed of aragonitic crystals (a form of calcium carbonate) with no free spicules (e.g. Vaceletia crypta, with
a continuous fossil record from the Middle Triassic, 245
My, to present). Others have a solid skeleton of either
linked or rigid calcareous spicules (e.g. Plectroninia hindei, with a body plan known from the Mid Miocene, 23
My) or a rigid basal mass of calcite, and some (the socalled ‘ lithistids’) have only siliceous skeletons composed of special spicules called desmas, ranging from
entirely fused and forming a rock hard skeleton to
loosely articulated rendering the body more flexible
(e.g. Theonella swinhoei, with ancestors recorded from
the Tertiary, 65 My). These so-called ‘living fossil’
sponges are usually found in shaded or dark habitats,
such as in crevices, deep caves or under coral rubble,
rarely in full light, and due to their hard coralline texture may be confused with corals by the novice. Similarly, caves and dark crevices are also home to a variety
of soft-bodied demosponges, sometimes lacking pigments (e.g. Petrosia ( Stongyl-ophora) strongylata), sometimes colourful (e.g. Ulosa spongia), and especially the
multitude of frequently brightly coloured calcareous
sponges living on the reef (e.g. Leucetta chagosensis, Levinella prolifera and Soleniscus radovani) (Fig. 17.4C–H).
Reef slope
Between the reef crest and the base of coral reefs, across
the shelf of the GBR, occur large, predominantly heterotrophic sponges that feed on food particles and waste
products filtering down from the coral reef above. On
some reefs, particularly those closer to the coast, these
faunas number several hundred species, which in some
instances occur as large populations. Their morphologies are as diverse as the conditions they live under,
such as flexible whips, fingers and fans adapted for coping with high currents (Ianthella basta, Axos flabelliformis,
Clathria (Thalysias) cervicornis); soft tubes, vases and
other shapes that predominate in silty, turbid water
where inhalant and exhalant pores are located on different surfaces to prevent smothering (e.g. Echinochalina
(Protophlitaspongia) isaaci and Fascaplysinopsis reticulata),
and a number of ubiquitous, amorphous, bulbous, massive, spherical (and other shaped) forms that appear
nearly anywhere they can settle and survive (e.g. Cinachyrella schulzei, Stylissa massa, Stylissa carteri, Acanthella
cavernosa, Amphimedon terpenensis, Pericharax heterorhaphis, and Agelas axifera) (Figs 17.5A–H, 17.6A–H).
Deeper lagoon and inter-reef
Sponges living on the seabed in between the reefs are
generally very different to those found on the coral
reefs, living in high current, low light, turbid waters
where they burrow into soft sandy and muddy sediments (e.g. Oceanapia renieroides and Disyringia dissimilis), in seagrass and Halimeda beds (e.g. Oceanapia
sagittaria), or attached to hard objects on the sea floor
(e.g. Xestospongia testudinaria, Melophlus sarassinorum
and Liosina paradoxa) (Fig. 17.7A, C, G, H). Growth
forms include elongate species with root-like tufts or
bulbs for anchoring in soft sediments and long tubes to
prevent smothering, flexible fans and whips in high
current areas, and massive barrels and volcanoes attached to rock and coral outcrops. This fauna comprises
a significant proportion of the ‘benthos’, providing important habitat for other marine species, ranging from
aggregating fishes to numerous crustacean in-faunas.
In a recent major survey across the length and breadth
of the GBR, conducted under the auspices of the
Cooperative Research Centre for the GBR (CRC Reef),
approximately 1300 morphospecies of sponges
were discovered from the inter-reef region, which is
particularly susceptible to human impacts such as
trawling (see also Chapter 6). Whereas a number of
species living on the coral reef flats may be found on
both sides of the Australian continent, these deeper
water GBR lagoonal and inter-reef species appear to
differ significantly in composition from the fauna found
at similar latitudes on the west coast of the continent.
Reef bioeroders (sponges as ‘parasites’)
A special group of sponges are responsible for significant carbonate recycling on the reef, collectively termed
excavating (‘boring’ or bioeroding) sponges (see also
Chapter 8). They are responsible for extensive damage