26
Reef Lime Constructions
3mmyear- 1 (Bardach 1961; P.J. Davies 1977; Frankel 1977). The rate of
erosion of the surface of consolidated lime rocks at flats in modern reefs,
which also reached stabilized sea, should be balanced against the vertical
growth of the consolidated reef-flat. The latter may be evaluated within
1-2mm or 2-4kgm- 2 of lime material per year. The rate of erosion should
be within the same range. Its direct estimate by using various me nth ods
resulted in the above-shown range (Table 1.5). This process is most active in
the intertidal zone. Deeper down it decreases more than ten times (Trudgill
1976).
The reef rocks show numerous signs of erosion in a multitude of various
channels, moats, trenches, holes and caves which cut their surfaces and
pierce their body (Ginsburg 1983). This erosion of the reef-flat rocks
proceeds mainly biologically, various boring animals and plants participating
in it. But also abiotic factors take a definite part in this process. The
mechanical erosion caused by them on reef surfaces is largely enhanced by
the abrasive impact of a mass of rubble moved by water. The reef rocks are
subjected also to an intensive weathering process connected with the
crystallization of marine salt inside their porous lime material during the
drying out of sea water left behind in it between the tides. The weathering is
intensified also by an excess of agressive CO2 formed by the decay of the
mass of organic matter produced by reef bottom communities. The
production of CO2 being accompanied by a drop in pH proceeds most
actively at night in pools remaining on reef-flats at low water. The waters of
lagoons are also enriched with free CO2 , especially at night. Passing over the
reef flat it dissolves the lime material on its surface, while microzones
enriched with free CO2 are also forming at night under the thalli of sea
weeds, rubble and detritus, as well as in numerous holes inhabited by their
owners - various benthic invertebrates and fish, which produce CO2 during
respiration. The reef rocks are perforated by numerous boring molds,
filamentous algae, worms, molluscs, and sponges (cf. Sect. 4.2). Their
surfaces are permanently scraped and grazed by benthic animals and fish,
which feed on periphyton and corals (Bak 1976; Trudgill 1983). The boring
molds belong to the genera Aspergillus, Cladosporum, Penicillum,
Phialophora (Kendrick et al. 1982). Among the boring algae penetrating
into the colonies of corals and into solid reef rocks, the most numerous are
the filamentous green algae Ostreobium and blue-green Hormatonema
(Alexandersson 1975; Kobluk and Risk 1977). Their filaments dissolve the
crystals of carbonate and penetrate into the rock material and il) the colonies
of dead and living corals.
The boring polychaete sponges and bivalves make a network of holes in
rock material as well as in coral colonies (Riitzler 1975; Hutchings 1985, cf.
Sects. 5.1.4, 5.2.3, 5.3). They undermine the mechanical durability of corals
and solid reef rocks exposed to the destroying action of surf. In regions of
cyclones, the activity of reef borers is the main cause of destruction of the
branching coral thickets on outer reef slopes and reef-flats (Warme 1977).
Reef Lime Constructions
3mmyear- 1 (Bardach 1961; P.J. Davies 1977; Frankel 1977). The rate of
erosion of the surface of consolidated lime rocks at flats in modern reefs,
which also reached stabilized sea, should be balanced against the vertical
growth of the consolidated reef-flat. The latter may be evaluated within
1-2mm or 2-4kgm- 2 of lime material per year. The rate of erosion should
be within the same range. Its direct estimate by using various me nth ods
resulted in the above-shown range (Table 1.5). This process is most active in
the intertidal zone. Deeper down it decreases more than ten times (Trudgill
1976).
The reef rocks show numerous signs of erosion in a multitude of various
channels, moats, trenches, holes and caves which cut their surfaces and
pierce their body (Ginsburg 1983). This erosion of the reef-flat rocks
proceeds mainly biologically, various boring animals and plants participating
in it. But also abiotic factors take a definite part in this process. The
mechanical erosion caused by them on reef surfaces is largely enhanced by
the abrasive impact of a mass of rubble moved by water. The reef rocks are
subjected also to an intensive weathering process connected with the
crystallization of marine salt inside their porous lime material during the
drying out of sea water left behind in it between the tides. The weathering is
intensified also by an excess of agressive CO2 formed by the decay of the
mass of organic matter produced by reef bottom communities. The
production of CO2 being accompanied by a drop in pH proceeds most
actively at night in pools remaining on reef-flats at low water. The waters of
lagoons are also enriched with free CO2 , especially at night. Passing over the
reef flat it dissolves the lime material on its surface, while microzones
enriched with free CO2 are also forming at night under the thalli of sea
weeds, rubble and detritus, as well as in numerous holes inhabited by their
owners - various benthic invertebrates and fish, which produce CO2 during
respiration. The reef rocks are perforated by numerous boring molds,
filamentous algae, worms, molluscs, and sponges (cf. Sect. 4.2). Their
surfaces are permanently scraped and grazed by benthic animals and fish,
which feed on periphyton and corals (Bak 1976; Trudgill 1983). The boring
molds belong to the genera Aspergillus, Cladosporum, Penicillum,
Phialophora (Kendrick et al. 1982). Among the boring algae penetrating
into the colonies of corals and into solid reef rocks, the most numerous are
the filamentous green algae Ostreobium and blue-green Hormatonema
(Alexandersson 1975; Kobluk and Risk 1977). Their filaments dissolve the
crystals of carbonate and penetrate into the rock material and il) the colonies
of dead and living corals.
The boring polychaete sponges and bivalves make a network of holes in
rock material as well as in coral colonies (Riitzler 1975; Hutchings 1985, cf.
Sects. 5.1.4, 5.2.3, 5.3). They undermine the mechanical durability of corals
and solid reef rocks exposed to the destroying action of surf. In regions of
cyclones, the activity of reef borers is the main cause of destruction of the
branching coral thickets on outer reef slopes and reef-flats (Warme 1977).