a nucleus (coral rubble, shell fragment, etc.) to form
rhodoliths. These are common in reefal environments
and growth rates of $1.6 mm/year have been determined
(Ballantine et al., 2000), although much slower growth
rates have also been suggested. In the Caribbean, filamentous algae are estimated to produce 700 g C/m
2
/year and
macroalgae 1,170 g C/m
2
/year (Rasser and Riegl, 2002),
whilst a study from Jamaica determined the carbonate
production of coralline algae using artificial tiles to be
between 70 and 150 g/m
2 /year (Mallela, 2007).
Modern reefal environments contain abundant algal
material but only few of those form mats and biofilms,
which trap, bind, and cement sedimentary material and
form accretionary structures. These binding structures of
which the finer-bound matrix is preserved, called stromatolites, dominated the shallow shelves during early Earth
(Allwood et al., 2006; Grotzinger and Knoll, 1999). At
present, shallow marine stromatolites occur around the
world but are often very limited in extent. The most
famous modern stromatolite occurrences are in Shark
Bay (Western Australia) (Logan, 1961), Lagoa Salgada
(Brazil) (Lemos et al., 1994), Highborne Cay and Exuma
Sound (Bahamas) (Dill et al., 1986; Dravis, 1983),
Teikehau Atoll (French Polynesia), Chetumal Bay
(Belize), etc. These structures are covered with biofilms
of microorganisms (in Shark Bay $90% cyanobacteria
and 10% archaea), which trap, bind, and cement sedimentary particles. Early work from Shark Bay showed that two
major types of stromatolites exist: (1) the eualgalcyanobacterial stromatolites (generally coarse grained)
and (2) the cyanobacterial stromatolites (fine grained)
(Awramik and Riding, 1988). There, the algal eukaryotes
produce subtidal columnar stromatolites due to their extracellular gel formation, which trap and bind sediment and
biogenic fragments (e.g., ooids, mollusks, diatoms). Similarly, the stromatolites from Exuma Sound (Bahamas) are
also coarse grained with dascylads and cyanobacteria,
which trap sands that are then bound and cemented by
acicular aragonite and chasmolithic green algae (Dravis,
1983). More recent investigations into the microorganisms associated with stromatolites demonstrated
a uniquely high diverse community of cyanobacteria, bacteria, and aechaea (Burns et al., 2004).
Polychaetes
Sedentary polychaetes, including serpulids, sabellariids,
and sabellids, are another important encrusting group of
organisms. Most polychaetes have a tube constructed by
sediment particles and mucus (organic compounds), in
which they live or grow erect attached to each other, which
may form large aggregates. The branchial crown of
sabellids functions both in respiration and in the collection
of suspended particulate matter from the surrounding water
(Bonar, 1972). The tube formation is a consequence of
burrowing as sand particles adhere to the mucous sheets
secreted by the mucous cells of the epidermis. The first portion built of the tube is a small, transparent mucous
cylinder, about 2-mm long (Kirtley, 1994). The worms
collect small fragments of minerals, diatom frustules,
sponge spicules, and other small objects of manageable size
and implant these reinforcements in the delicate mucus.
Later in their tube building, the worms choose among
a greater variety of materials. Into upper parts of the cylinder are set angular quartz grains, small fragments of broken
mollusk shells, fecal pellets, and other materials – all
arranged in an overlapping spiral pattern that rises to the
base of the flared opening. Tube formation and growth of
2.5–5 cm may occur within 2 months (Naylor and
Viles, 2000) and the tube particle sizes are often coarser
than the mean particle size of surrounding sand. In addition,
flat, platy and elongate particles are preferentially used.
A study from Florida showed that most sand particles
ranged between 0.25 and 0.5 mm (Main and Nelson,
1988). In the Caribbean, analysis of modern polychaete
worm tubes showed distinct micritic peloidal lamellae
morphologies (Fischer et al., 2000). Histological investigation of the tubes of Dodecaceria showed that the tube
formation is related to two processes. The initial process
is weakly controlled by the worm itself (matrix mediated).
The worm produces acidic organic mucus substances,
which are enriched between the soft tissue and the tube
wall. The mucus has an antifouling capability and inhibits
the mineralization of the mucus for a certain time. Within
polychaete tubes, the mineralization events of the mucus
are responsible for the stromatolitic microfabric of the
tubes. Within the spaces between the primary lamellae,
nonspecific extracellular polymeric substances–rich mucus
is enriched, which controls the formation of fibrous aragonitic crystals and peloidal fabrics. Hence, the mucus plays
an important role during the organomineralization process,
which is not controlled directly by the organism (Fischer
et al., 2000).
Sabellariid reefs flourish best where vigorous wave and
current action cause the suspension and transport of sandsize particles (Kirtley, 1994). In some areas (e.g., east and
northeast Brazil and southwest India), sabellariid reefs
may extend laterally for thousands of kilometers along
the shores of modern seas (Pandolfi et al., 1998). The
sabellariids occur in densities as many as 15,000–60,000
individuals/m
2 and are known to have life spans as long
as 10½ years (Kirtley, 1994). Aggregations of sabellariid
worms create geological formations called worm reefs
(Main and Nelson, 1988) and have been reported from
around the globe, including Europe (Kirtley, 1992; Naylor
and Viles, 2000), Taiwan (Chen and Dai, 2009), Hawaii
(Pandolfi et al., 1998), Fiji (Bailey-Brock et al., 2009), etc.
Summary and conclusion
Coral reef environments host many organisms that
actively precipitate mineral matter, encrust or bind sedimentary particles together. The binding organisms of
modern reefal ecosystems are critically important as they
contribute calcium carbonates to the reef framework, bind
particles and rubble and thus stabilize the substrate, and
BINDING ORGANISMS
137
rhodoliths. These are common in reefal environments
and growth rates of $1.6 mm/year have been determined
(Ballantine et al., 2000), although much slower growth
rates have also been suggested. In the Caribbean, filamentous algae are estimated to produce 700 g C/m
2
/year and
macroalgae 1,170 g C/m
2
/year (Rasser and Riegl, 2002),
whilst a study from Jamaica determined the carbonate
production of coralline algae using artificial tiles to be
between 70 and 150 g/m
2 /year (Mallela, 2007).
Modern reefal environments contain abundant algal
material but only few of those form mats and biofilms,
which trap, bind, and cement sedimentary material and
form accretionary structures. These binding structures of
which the finer-bound matrix is preserved, called stromatolites, dominated the shallow shelves during early Earth
(Allwood et al., 2006; Grotzinger and Knoll, 1999). At
present, shallow marine stromatolites occur around the
world but are often very limited in extent. The most
famous modern stromatolite occurrences are in Shark
Bay (Western Australia) (Logan, 1961), Lagoa Salgada
(Brazil) (Lemos et al., 1994), Highborne Cay and Exuma
Sound (Bahamas) (Dill et al., 1986; Dravis, 1983),
Teikehau Atoll (French Polynesia), Chetumal Bay
(Belize), etc. These structures are covered with biofilms
of microorganisms (in Shark Bay $90% cyanobacteria
and 10% archaea), which trap, bind, and cement sedimentary particles. Early work from Shark Bay showed that two
major types of stromatolites exist: (1) the eualgalcyanobacterial stromatolites (generally coarse grained)
and (2) the cyanobacterial stromatolites (fine grained)
(Awramik and Riding, 1988). There, the algal eukaryotes
produce subtidal columnar stromatolites due to their extracellular gel formation, which trap and bind sediment and
biogenic fragments (e.g., ooids, mollusks, diatoms). Similarly, the stromatolites from Exuma Sound (Bahamas) are
also coarse grained with dascylads and cyanobacteria,
which trap sands that are then bound and cemented by
acicular aragonite and chasmolithic green algae (Dravis,
1983). More recent investigations into the microorganisms associated with stromatolites demonstrated
a uniquely high diverse community of cyanobacteria, bacteria, and aechaea (Burns et al., 2004).
Polychaetes
Sedentary polychaetes, including serpulids, sabellariids,
and sabellids, are another important encrusting group of
organisms. Most polychaetes have a tube constructed by
sediment particles and mucus (organic compounds), in
which they live or grow erect attached to each other, which
may form large aggregates. The branchial crown of
sabellids functions both in respiration and in the collection
of suspended particulate matter from the surrounding water
(Bonar, 1972). The tube formation is a consequence of
burrowing as sand particles adhere to the mucous sheets
secreted by the mucous cells of the epidermis. The first portion built of the tube is a small, transparent mucous
cylinder, about 2-mm long (Kirtley, 1994). The worms
collect small fragments of minerals, diatom frustules,
sponge spicules, and other small objects of manageable size
and implant these reinforcements in the delicate mucus.
Later in their tube building, the worms choose among
a greater variety of materials. Into upper parts of the cylinder are set angular quartz grains, small fragments of broken
mollusk shells, fecal pellets, and other materials – all
arranged in an overlapping spiral pattern that rises to the
base of the flared opening. Tube formation and growth of
2.5–5 cm may occur within 2 months (Naylor and
Viles, 2000) and the tube particle sizes are often coarser
than the mean particle size of surrounding sand. In addition,
flat, platy and elongate particles are preferentially used.
A study from Florida showed that most sand particles
ranged between 0.25 and 0.5 mm (Main and Nelson,
1988). In the Caribbean, analysis of modern polychaete
worm tubes showed distinct micritic peloidal lamellae
morphologies (Fischer et al., 2000). Histological investigation of the tubes of Dodecaceria showed that the tube
formation is related to two processes. The initial process
is weakly controlled by the worm itself (matrix mediated).
The worm produces acidic organic mucus substances,
which are enriched between the soft tissue and the tube
wall. The mucus has an antifouling capability and inhibits
the mineralization of the mucus for a certain time. Within
polychaete tubes, the mineralization events of the mucus
are responsible for the stromatolitic microfabric of the
tubes. Within the spaces between the primary lamellae,
nonspecific extracellular polymeric substances–rich mucus
is enriched, which controls the formation of fibrous aragonitic crystals and peloidal fabrics. Hence, the mucus plays
an important role during the organomineralization process,
which is not controlled directly by the organism (Fischer
et al., 2000).
Sabellariid reefs flourish best where vigorous wave and
current action cause the suspension and transport of sandsize particles (Kirtley, 1994). In some areas (e.g., east and
northeast Brazil and southwest India), sabellariid reefs
may extend laterally for thousands of kilometers along
the shores of modern seas (Pandolfi et al., 1998). The
sabellariids occur in densities as many as 15,000–60,000
individuals/m
2 and are known to have life spans as long
as 10½ years (Kirtley, 1994). Aggregations of sabellariid
worms create geological formations called worm reefs
(Main and Nelson, 1988) and have been reported from
around the globe, including Europe (Kirtley, 1992; Naylor
and Viles, 2000), Taiwan (Chen and Dai, 2009), Hawaii
(Pandolfi et al., 1998), Fiji (Bailey-Brock et al., 2009), etc.
Summary and conclusion
Coral reef environments host many organisms that
actively precipitate mineral matter, encrust or bind sedimentary particles together. The binding organisms of
modern reefal ecosystems are critically important as they
contribute calcium carbonates to the reef framework, bind
particles and rubble and thus stabilize the substrate, and
BINDING ORGANISMS
137