The Great Barrier Reef
186
which the sponge cells interact at various levels (from
predation to commensalism). In addition to nutrients
acquired through filter feeding activities sponges may
ingest a myriad of toxic chemicals excreted by other
plants and animals from the coral reefs above, which
they modify (sequester) and reuse for their own purposes. The combination of chemicals produced by
normal sponge metabolism, those sequestered from
the seawater, and those produced by or in combination with the resident microbial populations makes
sponges among the most toxic of all life forms, and
hence of great interest to the pharmaceutical industry
(Box 17.1 and Fig. 17.2).
N PREDATION AND DEFENCE
Sponges are most unappetising by human standards
due to a combination of high toxicity and a generally
low ratio of soft tissue to mineral skeleton. The ability
to digest and modify the waste products and chemicals produced by other organisms which live in, on or
near sponges may at least partly account for their diverse, frequently novel and often highly toxic biochemistry. Nevertheless, sponges do have many
recorded predators such as molluscs, echinoderms,
fishes and turtles. On the GBR and in north-western
Australia, sea cucumbers (Synaptula species) are frequently seen congregating on sponges (in particular
branching and lamellate Haliclona, Axos and Ianthella
species), feeding on the mucus exudate. Nudibranchs
are also active feeders on sponge mucus and collagen, and sometimes these molluscs are quite specific
as to the species or genus of sponge upon which they
prey. Nudibranchs also ingest the sponge’s toxic
chemicals, concentrating, modifying and reusing (sequestering) them for their own chemical protection.
The predators are often the same colour as the sponge,
having ingested the sponge’s characteristically
brightly coloured carotenoid pigments. Other documented predators of sponges on the GBR include
green and hawksbill turtles, many species of grazing
fishes and asteroid, ophiuroid and holothurian echinoderms. There is now some good evidence to show
that sponges also use their extensive arsenal of chemicals as both offensive and defensive weapons, such
as repelling predators, deterring parasites and competing for space, and that the concentration, toxicity
and/or secondary modification of particular compounds may vary seasonally and in response to predation intensity.
N PRESERVATION AND IDENTIFICATION
An information sheet on collecting, preserving, histological preparation and lists of characters used for
identification of sponges can be found on the web (see
Additional reading). Collection of sponges within the
Marine Park requires a permit and should also be undertaken with care (both for the sponge and the collector), owing to the often fragile nature of many
specimens that disintegrate upon collection, and the
sharp spicules and toxic mucus/chemicals that may
injure the collector. Underwater and/or on-deck photographs of living specimens are highly recommended
given that body shape and colouration may change
dramatically following preservation. Freezing specimens prior to their preservation may be useful to fix
soluble pigments in colourful species. Sponges are
generally preserved separately in 70–80% ethanol,
with care taken to prevent leaching of pigments between samples, particularly those with aerophobic
pigments that change from yellow to blue and may
stain entire collections. Formaldehyde preservative
should be avoided for most sponges although it is used
briefly as a fixative for calcareans, and air dried specimens are virtually useless for taxonomic identification.
Other specialised fixatives include gluteraldehyde for
detailed cellular ultrastructure studies (do not freeze),
and 100% ethanol, DMSO or laboratory grade silica gel
for storage of DNA samples. Routine histology is required for identification, and includes nitric acid or
chlorine bleach digestion of the silica and calcitic spicule skeletons, respectively. Thin sections of the whole
skeleton can be hand or microtome cut to include details of the ectosome and choanosome. Staining sections for different cellular elements and scanning
electron microscopy are now widely used. Keys to orders, families and genera (see Additional reading) are
largely based on features of the inorganic and organic
skeletons.
186
which the sponge cells interact at various levels (from
predation to commensalism). In addition to nutrients
acquired through filter feeding activities sponges may
ingest a myriad of toxic chemicals excreted by other
plants and animals from the coral reefs above, which
they modify (sequester) and reuse for their own purposes. The combination of chemicals produced by
normal sponge metabolism, those sequestered from
the seawater, and those produced by or in combination with the resident microbial populations makes
sponges among the most toxic of all life forms, and
hence of great interest to the pharmaceutical industry
(Box 17.1 and Fig. 17.2).
N PREDATION AND DEFENCE
Sponges are most unappetising by human standards
due to a combination of high toxicity and a generally
low ratio of soft tissue to mineral skeleton. The ability
to digest and modify the waste products and chemicals produced by other organisms which live in, on or
near sponges may at least partly account for their diverse, frequently novel and often highly toxic biochemistry. Nevertheless, sponges do have many
recorded predators such as molluscs, echinoderms,
fishes and turtles. On the GBR and in north-western
Australia, sea cucumbers (Synaptula species) are frequently seen congregating on sponges (in particular
branching and lamellate Haliclona, Axos and Ianthella
species), feeding on the mucus exudate. Nudibranchs
are also active feeders on sponge mucus and collagen, and sometimes these molluscs are quite specific
as to the species or genus of sponge upon which they
prey. Nudibranchs also ingest the sponge’s toxic
chemicals, concentrating, modifying and reusing (sequestering) them for their own chemical protection.
The predators are often the same colour as the sponge,
having ingested the sponge’s characteristically
brightly coloured carotenoid pigments. Other documented predators of sponges on the GBR include
green and hawksbill turtles, many species of grazing
fishes and asteroid, ophiuroid and holothurian echinoderms. There is now some good evidence to show
that sponges also use their extensive arsenal of chemicals as both offensive and defensive weapons, such
as repelling predators, deterring parasites and competing for space, and that the concentration, toxicity
and/or secondary modification of particular compounds may vary seasonally and in response to predation intensity.
N PRESERVATION AND IDENTIFICATION
An information sheet on collecting, preserving, histological preparation and lists of characters used for
identification of sponges can be found on the web (see
Additional reading). Collection of sponges within the
Marine Park requires a permit and should also be undertaken with care (both for the sponge and the collector), owing to the often fragile nature of many
specimens that disintegrate upon collection, and the
sharp spicules and toxic mucus/chemicals that may
injure the collector. Underwater and/or on-deck photographs of living specimens are highly recommended
given that body shape and colouration may change
dramatically following preservation. Freezing specimens prior to their preservation may be useful to fix
soluble pigments in colourful species. Sponges are
generally preserved separately in 70–80% ethanol,
with care taken to prevent leaching of pigments between samples, particularly those with aerophobic
pigments that change from yellow to blue and may
stain entire collections. Formaldehyde preservative
should be avoided for most sponges although it is used
briefly as a fixative for calcareans, and air dried specimens are virtually useless for taxonomic identification.
Other specialised fixatives include gluteraldehyde for
detailed cellular ultrastructure studies (do not freeze),
and 100% ethanol, DMSO or laboratory grade silica gel
for storage of DNA samples. Routine histology is required for identification, and includes nitric acid or
chlorine bleach digestion of the silica and calcitic spicule skeletons, respectively. Thin sections of the whole
skeleton can be hand or microtome cut to include details of the ectosome and choanosome. Staining sections for different cellular elements and scanning
electron microscopy are now widely used. Keys to orders, families and genera (see Additional reading) are
largely based on features of the inorganic and organic
skeletons.