densities between sites, with high island sites being
favored over atoll sites, but no clear relationships were
seen with regards to water quality, in part due perhaps to
relatively low numbers of recruits to all sites over the 5
years of the experiment. Another reason may have been
that all these sites had similar depths and exposure, two
factors which Rice and Macintyre (1982) suggest are
important in determining distributions of this group.
Sipunculans are rarely found in coral substrates which
are not covered with algae and epifauna and this is probably because boring sipunculans feed on debris and sand
trapped in biota. They do not occur in the living portions
of the coral colonies (Rice and Macintyre, 1982).
While most sipunculans recruit by pelagic larvae,
Aspidosiphon brocki is known to reproduce asexually as
well by constricting the posterior end to form a new individual which is then retained in the burrow (Rice, 1970).
Mechanism of boring by sipunculans
Rice and Macintyre (1972) investigated sipunculan burrows using thin sections and studied three species; and
they found fine carbonate skeletal grains in the walls of
most burrows examined suggesting that some mechanical
abrasion has occurred during the formation of them. However, this skeletal material was not always identical to the
framework in which the burrow was created, and they postulate that that it was debris associated with sponge boring
on the walls of the burrow, or debris which had fallen into
the burrow or internal sediment infill which was present
before the sipunculan began to bore. They did find evidence of chemical dissolution as some of the coralline
algal fragments and lithified internal sediment was different to the walls of some burrows. However, not all
burrows exhibited these changes and they concluded
that both mechanical abrasion and chemical action are
involved in burrow formation. Warme (1975) concurs
with this and he suggests that the variety of hooks, spines,
or papillae embedded in the leathery skin of sipunculans
may anchor the worm while they are boring into the substrate and perhaps aid in the mechanical grinding of acid
softened substrate (Warme, 1975). Their borings are variable, most are simple, blind, straight to gently curved or
sometimes highly sinous tubes, containing a single specimen (Rice, 1969; Rice and Macintyre, 1972).
Fossil data for sipunculans
Fossil sipunculans have been recorded from the Burgess
Shale, although some workers have disputed this, but no
records from fossil reefs could be found.
Sponges
Diversity of sponges
The following Orders of sponges include bioeroders,
Hadromerida (Clionaidae, perhaps Spirastrellidae, and the
Alectonidae), the Poecilosclerida (Acarnidae, i.e., the genus
Zyzzya), the Halichondrida (Halichondriidae, i.e., the genus
Amorphinopsis), and the Haplosclerida (Phloeodictyidae,
i.e., the genus Aka) and there are a few “maybe eroders”
in other Orders (Hooper and van Soest, 2002; Schönberg,
pers. comm.). This suggests that the ability to bioerode
has developed several times within the Porifera.
The taxonomy of sponges is currently undergoing major
revisions as many of the so called “cosmopolitan” species
are being described as suites of new species based on
molecular data, even though it is difficult to separate them
morphologically (Xavier et al., in press). Ongoing revisions
of bioeroding sponges indicate that they are more diverse in
the Indo-Pacific (Schönberg, pers. comm.) than in the
Atlantic even though the Atlantic communities are far better
studied (e.g., Rosell and Uriz, 1997). A phylogenetic study
of the genus Cliona has clearly shown that it is polyphyletic
group but Rosell and Uriz (1997) preferred to maintain the
genus until more detailed information was available on
a wider range of taxa within this group.
Succession of sponges
While no data appears to exist on possible succession of
species in coral substrates over time, there has been a
widely held view that species may exhibit various growth
forms with age. It has been suggested that there is an initial alpha (=papillate), later beta (=encrusting), and then
a gamma-massive free living morphology (Hartman,
1958). However, Schönberg (2008) does suggest that
as no single species has ever been followed from settlement to the free living form, and not all growth forms
are found within a single habitat, and as most species are
known only as alpha-papillate forms, it may be that different growth forms represent different species. However,
Rützler (pers. comm.) disputes this and suggest that some
gamma stages have been wrongly linked to certain alpha
stages (e.g., Cliona nigrescens to C. viridis, in the Mediterranean). This apparent ability of some species to exhibit
different growth forms could be very useful for taxonomy
together with molecular data which is increasingly being
used to separate species.
Recruitment of sponges
Recruitment is via pelagic larvae, but information on seasonality is not available. The clionaid sponges, one of the
dominant boring groups, are found in both dead and live
coral as their larvae have the ability to survive direct contact with coral polyps, but their ecological success at
invading coral substrates is largely due to their ability to
undermine and erode the coral skeletal base which is typically dead, thus avoiding contact with the defensive
mucus and nematocysts of the coral polyp.
López-Victoria and Zea (2004) working in the Caribbean found that sponge bored fragments of coral could
be redistributed across the reef and infect new coral fragments. This method of colonization can result in rapid
build up of populations and may occur often after storm
events.
Mechanism of boring by sponges
Detailed studies have been undertaken on the way in
which sponges bore (Rützler and Rieger 1973; Pomponi,
144
BIOEROSION
favored over atoll sites, but no clear relationships were
seen with regards to water quality, in part due perhaps to
relatively low numbers of recruits to all sites over the 5
years of the experiment. Another reason may have been
that all these sites had similar depths and exposure, two
factors which Rice and Macintyre (1982) suggest are
important in determining distributions of this group.
Sipunculans are rarely found in coral substrates which
are not covered with algae and epifauna and this is probably because boring sipunculans feed on debris and sand
trapped in biota. They do not occur in the living portions
of the coral colonies (Rice and Macintyre, 1982).
While most sipunculans recruit by pelagic larvae,
Aspidosiphon brocki is known to reproduce asexually as
well by constricting the posterior end to form a new individual which is then retained in the burrow (Rice, 1970).
Mechanism of boring by sipunculans
Rice and Macintyre (1972) investigated sipunculan burrows using thin sections and studied three species; and
they found fine carbonate skeletal grains in the walls of
most burrows examined suggesting that some mechanical
abrasion has occurred during the formation of them. However, this skeletal material was not always identical to the
framework in which the burrow was created, and they postulate that that it was debris associated with sponge boring
on the walls of the burrow, or debris which had fallen into
the burrow or internal sediment infill which was present
before the sipunculan began to bore. They did find evidence of chemical dissolution as some of the coralline
algal fragments and lithified internal sediment was different to the walls of some burrows. However, not all
burrows exhibited these changes and they concluded
that both mechanical abrasion and chemical action are
involved in burrow formation. Warme (1975) concurs
with this and he suggests that the variety of hooks, spines,
or papillae embedded in the leathery skin of sipunculans
may anchor the worm while they are boring into the substrate and perhaps aid in the mechanical grinding of acid
softened substrate (Warme, 1975). Their borings are variable, most are simple, blind, straight to gently curved or
sometimes highly sinous tubes, containing a single specimen (Rice, 1969; Rice and Macintyre, 1972).
Fossil data for sipunculans
Fossil sipunculans have been recorded from the Burgess
Shale, although some workers have disputed this, but no
records from fossil reefs could be found.
Sponges
Diversity of sponges
The following Orders of sponges include bioeroders,
Hadromerida (Clionaidae, perhaps Spirastrellidae, and the
Alectonidae), the Poecilosclerida (Acarnidae, i.e., the genus
Zyzzya), the Halichondrida (Halichondriidae, i.e., the genus
Amorphinopsis), and the Haplosclerida (Phloeodictyidae,
i.e., the genus Aka) and there are a few “maybe eroders”
in other Orders (Hooper and van Soest, 2002; Schönberg,
pers. comm.). This suggests that the ability to bioerode
has developed several times within the Porifera.
The taxonomy of sponges is currently undergoing major
revisions as many of the so called “cosmopolitan” species
are being described as suites of new species based on
molecular data, even though it is difficult to separate them
morphologically (Xavier et al., in press). Ongoing revisions
of bioeroding sponges indicate that they are more diverse in
the Indo-Pacific (Schönberg, pers. comm.) than in the
Atlantic even though the Atlantic communities are far better
studied (e.g., Rosell and Uriz, 1997). A phylogenetic study
of the genus Cliona has clearly shown that it is polyphyletic
group but Rosell and Uriz (1997) preferred to maintain the
genus until more detailed information was available on
a wider range of taxa within this group.
Succession of sponges
While no data appears to exist on possible succession of
species in coral substrates over time, there has been a
widely held view that species may exhibit various growth
forms with age. It has been suggested that there is an initial alpha (=papillate), later beta (=encrusting), and then
a gamma-massive free living morphology (Hartman,
1958). However, Schönberg (2008) does suggest that
as no single species has ever been followed from settlement to the free living form, and not all growth forms
are found within a single habitat, and as most species are
known only as alpha-papillate forms, it may be that different growth forms represent different species. However,
Rützler (pers. comm.) disputes this and suggest that some
gamma stages have been wrongly linked to certain alpha
stages (e.g., Cliona nigrescens to C. viridis, in the Mediterranean). This apparent ability of some species to exhibit
different growth forms could be very useful for taxonomy
together with molecular data which is increasingly being
used to separate species.
Recruitment of sponges
Recruitment is via pelagic larvae, but information on seasonality is not available. The clionaid sponges, one of the
dominant boring groups, are found in both dead and live
coral as their larvae have the ability to survive direct contact with coral polyps, but their ecological success at
invading coral substrates is largely due to their ability to
undermine and erode the coral skeletal base which is typically dead, thus avoiding contact with the defensive
mucus and nematocysts of the coral polyp.
López-Victoria and Zea (2004) working in the Caribbean found that sponge bored fragments of coral could
be redistributed across the reef and infect new coral fragments. This method of colonization can result in rapid
build up of populations and may occur often after storm
events.
Mechanism of boring by sponges
Detailed studies have been undertaken on the way in
which sponges bore (Rützler and Rieger 1973; Pomponi,
144
BIOEROSION