1977, 1979a, b, and the history of sponge boring studies
has been reviewed extensively by Schönberg 2008).
Sponge erosion involves chemical etching of the substrate
producing cup-shaped fissures and the mechanical removal
of the resultant sponge chips through the sponge oscula and
carried away by water currents (Neumann, 1966; Rützler
and Rieger, 1973; Hatch, 1980). The etching agents are
produced by specialized etching cells with filopodia
which allows very localized application of the agents and
enzymes. Pomponi (1977, 1979a, b) undertook detailed
studies on the ultrastructure of these etching cells and she
suggests that they are capable of protein synthesis, absorption, and intracellular digestion. She also found that carbonic anhydrase activity was associated with etching cell
bodies, their filopodia and the spaces between them,
whereas acid phosphatase activity was most intense on the
outer surfaces of the cell processes but also detectable in
the cell organelles. She argued that phosphatase was
involved in the extra- and intracellular digestion of the
organic compounds of the substrate, and carbonic anhydrase
in the dissolution of the mineral components (Pomponi,
1980). Hatch (1980) was the first worker to provide the biochemical evidence to support the shifting of the carbonate
equilibrium and he discusses how substrate dissolution
may occur. Although Rützler and Rieger (1973) suggest that
only 2–3% of the eroded substrate is chemically dissolved
and the remaining removed mechanically, recent studies
by Zundelevich et al. (2007) suggest that far more is
removed by chemical dissolution but Schönberg (2008)
questions this. It may be that this ratio varies according to
the group and may shift with changing environments (e.g.,
with ocean acidification).
Sponge boring produces characteristic traces, which are
called “chambers” in the substrate which often end in
minute pioneering ducts. The macroscopic patterns of
chamber size and distribution have traditionally been
used for taxonomic purposes (e.g., Rützler, 1974) or for
measuring rates of boring (Rose and Risk, 1985). However, it has been clearly shown that a species can produce more than one kind of trace, a single trace may
have been produced by several sponge species (Bromley
and D’Alessandro, 1989), and these are influenced by
many environmental factors, such as substrate density,
water flow, and quality (Schönberg 2008). Boring also
produces sponge chips which are dislodged mechanically
and then transported out of the sponge galleries. These
chips have characteristic shapes and morphologies which
can be easily recognized in sediments, including lagoonal,
inter reefal areas, concretions within previously bored
substrates, etc.
Species determination can be difficult and chip dimensions have been used with some success to separate species, but sponge chip and sponge scar dimensions vary
within the substrate whereas genera can be differentiated
based on spicule shapes.
They tend to be larger in central established regions of
the sponge boring, and with smaller diameters in pioneer
regions (Rützler and Rieger, 1973). They also vary with
substrate type. Calcinai et al. (2008) working on a species
of Cliona found that while microsculpturing of scars was
similar in different substrates, other microscopic and macroscopic traces varied with substrate. They suggest this is
due to the substrate microtexture.
Rates of boring
Variations in rates of boring by sponges experimentally
(Bak, 1976 and references therein) suggest that rates
vary according to species of sponge, substrate density
(Highsmith et al., 1983; Rose and Risk, 1985; Edinger
and Risk, 1997), location and depth (López-Victoria and
Zea, 2005) on the reef. More material is removed from
massive corals with less porous skeletons than from less
massive more porous species (Buddemeier et al., 1974)
and this has also been observed for the other macroborers
(Hutchings, pers. observ.). Based on field observations
from many geographical locations and experimental studies, other factors are also important in determining rates
and abundances of boring sponges such as water flow
(López-Victoria and Zea, 2005); nutrient or sewage concentration (Hutchings et al., 2005; Holmes, 2000; Holmes
et al., 2000); temperature with rates in the Red Sea varying
with season, and being lower in cooler areas (Mokady
et al., 1993; Zundelevich et al., 2007); and light especially
if the sponge has symbiotic algae (López-Victoria and
Zea, 2005). On impacted reefs, where many species are
under stress, boring sponges thrive (Rützler, 2002;
Márquez et al., 2006). Finally, rates are not constant over
time with larvae or fragments freshly settling or attaching,
having higher rates of growth and erosion; in contrast
established colonies exhibit slow growth and low rates
of erosion (Neumann, 1966; Rützler, 1975).
Habitat modification by sponges
Sponges are important in modifying habitats through
bioerosion, and often physically support corals, preventing collapse after their basal structure has been eroded
(Goreau and Hartman, 1963). They are also important in
reef framework consolidation as they hold corals and rubble together during sediment infilling and lithification
(see Wilkinson, 1983, for more details). Encrusting species of boring sponges can overgrow neighboring corals
(López-Victoria and Zea, 2004; López-Victoria et al.,
2006) and kill the corals.
Sponges in the fossil record
Sponges were among the first metazoans to occur in the
geological records. The first reefs that were constructed
primarily by sponges were in the late Ordovician period,
where sponges had massive, fused, calcareous skeletons,
the Stromatoporidea (Wilkinson, 1983). Kobluk and van
Soest (1989) suggest that as sponges have limited preservable skeletal material, the fossil record on later reefs may
be a poor representation of their importance in fossil reef
systems, although the burrows would still be apparent.
BIOEROSION
145
has been reviewed extensively by Schönberg 2008).
Sponge erosion involves chemical etching of the substrate
producing cup-shaped fissures and the mechanical removal
of the resultant sponge chips through the sponge oscula and
carried away by water currents (Neumann, 1966; Rützler
and Rieger, 1973; Hatch, 1980). The etching agents are
produced by specialized etching cells with filopodia
which allows very localized application of the agents and
enzymes. Pomponi (1977, 1979a, b) undertook detailed
studies on the ultrastructure of these etching cells and she
suggests that they are capable of protein synthesis, absorption, and intracellular digestion. She also found that carbonic anhydrase activity was associated with etching cell
bodies, their filopodia and the spaces between them,
whereas acid phosphatase activity was most intense on the
outer surfaces of the cell processes but also detectable in
the cell organelles. She argued that phosphatase was
involved in the extra- and intracellular digestion of the
organic compounds of the substrate, and carbonic anhydrase
in the dissolution of the mineral components (Pomponi,
1980). Hatch (1980) was the first worker to provide the biochemical evidence to support the shifting of the carbonate
equilibrium and he discusses how substrate dissolution
may occur. Although Rützler and Rieger (1973) suggest that
only 2–3% of the eroded substrate is chemically dissolved
and the remaining removed mechanically, recent studies
by Zundelevich et al. (2007) suggest that far more is
removed by chemical dissolution but Schönberg (2008)
questions this. It may be that this ratio varies according to
the group and may shift with changing environments (e.g.,
with ocean acidification).
Sponge boring produces characteristic traces, which are
called “chambers” in the substrate which often end in
minute pioneering ducts. The macroscopic patterns of
chamber size and distribution have traditionally been
used for taxonomic purposes (e.g., Rützler, 1974) or for
measuring rates of boring (Rose and Risk, 1985). However, it has been clearly shown that a species can produce more than one kind of trace, a single trace may
have been produced by several sponge species (Bromley
and D’Alessandro, 1989), and these are influenced by
many environmental factors, such as substrate density,
water flow, and quality (Schönberg 2008). Boring also
produces sponge chips which are dislodged mechanically
and then transported out of the sponge galleries. These
chips have characteristic shapes and morphologies which
can be easily recognized in sediments, including lagoonal,
inter reefal areas, concretions within previously bored
substrates, etc.
Species determination can be difficult and chip dimensions have been used with some success to separate species, but sponge chip and sponge scar dimensions vary
within the substrate whereas genera can be differentiated
based on spicule shapes.
They tend to be larger in central established regions of
the sponge boring, and with smaller diameters in pioneer
regions (Rützler and Rieger, 1973). They also vary with
substrate type. Calcinai et al. (2008) working on a species
of Cliona found that while microsculpturing of scars was
similar in different substrates, other microscopic and macroscopic traces varied with substrate. They suggest this is
due to the substrate microtexture.
Rates of boring
Variations in rates of boring by sponges experimentally
(Bak, 1976 and references therein) suggest that rates
vary according to species of sponge, substrate density
(Highsmith et al., 1983; Rose and Risk, 1985; Edinger
and Risk, 1997), location and depth (López-Victoria and
Zea, 2005) on the reef. More material is removed from
massive corals with less porous skeletons than from less
massive more porous species (Buddemeier et al., 1974)
and this has also been observed for the other macroborers
(Hutchings, pers. observ.). Based on field observations
from many geographical locations and experimental studies, other factors are also important in determining rates
and abundances of boring sponges such as water flow
(López-Victoria and Zea, 2005); nutrient or sewage concentration (Hutchings et al., 2005; Holmes, 2000; Holmes
et al., 2000); temperature with rates in the Red Sea varying
with season, and being lower in cooler areas (Mokady
et al., 1993; Zundelevich et al., 2007); and light especially
if the sponge has symbiotic algae (López-Victoria and
Zea, 2005). On impacted reefs, where many species are
under stress, boring sponges thrive (Rützler, 2002;
Márquez et al., 2006). Finally, rates are not constant over
time with larvae or fragments freshly settling or attaching,
having higher rates of growth and erosion; in contrast
established colonies exhibit slow growth and low rates
of erosion (Neumann, 1966; Rützler, 1975).
Habitat modification by sponges
Sponges are important in modifying habitats through
bioerosion, and often physically support corals, preventing collapse after their basal structure has been eroded
(Goreau and Hartman, 1963). They are also important in
reef framework consolidation as they hold corals and rubble together during sediment infilling and lithification
(see Wilkinson, 1983, for more details). Encrusting species of boring sponges can overgrow neighboring corals
(López-Victoria and Zea, 2004; López-Victoria et al.,
2006) and kill the corals.
Sponges in the fossil record
Sponges were among the first metazoans to occur in the
geological records. The first reefs that were constructed
primarily by sponges were in the late Ordovician period,
where sponges had massive, fused, calcareous skeletons,
the Stromatoporidea (Wilkinson, 1983). Kobluk and van
Soest (1989) suggest that as sponges have limited preservable skeletal material, the fossil record on later reefs may
be a poor representation of their importance in fossil reef
systems, although the burrows would still be apparent.
BIOEROSION
145