Biological Factors of Formation and Erosion
Table 1.6. Annual rates and depths of erosion of reef-fiat
rock surfaces in the intertidal zone; data by Davies (1983);
Riitzler (1975), Trudgill (1976), Hudson (1977), Bromley
(1978)
Location
Florida
Bikini atoll
Bermuda
Australia
GBR of Australia
Aldabra atoll (upper part of
intertidal zone)
Same, medium part
Same, lower part
3-13
1
2.4-7.0
1-2
0.4-6.0
1.3-9.0
2.2-2.6
1.1-4.4
Depth (mm)
1.5-6.0
0.5
1.2
0.5-1
0.2-2.9
0.6-4.0
1-3
0.5-2.0
27
Among the most common benthic reef borers there should be mentioned
the sponges Ciiona, Anthosigmella, Siphonodyction, the bivalves
Lithophaga,
Gastrochaena,
Petricola,
the
vermetid
gastropods
Dendropoma, the sipunculid worms Phascolosoma, the polychaetes Eunice
(miticulata), Polydora, Fabricinus, Hypiscomus (elegans), the barnacles
Lithophrya (dorsalis), and the urchins Echinometra. On reef flats off the
Virgin Islands, in a zone covered by coralline algae, they are active over
30% of their total surface, thus furthering their destruction by surf (Adey
1975; Bak 1989).
An approximate estimate of the rate of erosion of reef-flat rock gives its
annual value as up to several kg m -2 (Table 1.6). Alone the boring sponges
in places of infestation may destroy 7-20kgm- 2 year- 1 of solid reef rock,
which could be much more than the possible calcification rate. Average
rates of bioerosion were evaluated to be within 0.4 kg m -2 (Stearn et al.
1977). The share of bioerosion comprises about two thirds of the total
(Trudgill 1976).
The mass of carbonate material produced by the erosion of reef into
rubble and sand is transported by surf and currents and also by migrating
animals (mainly by fish) ingesting the lime material to other zones of the
reef. So the bioerosion of solid reef rocks is one of the main sources of
formation of soft reef sediments (Stearn et al. 1977; Davies 1983). The
reef-flat of modern reefs, whose vertical growth was stopped by the recent
stabilization of the sea-level, became the zone of intensive production of
friable lime material. Transferred out to the leeward side of the reef it is
contributing to the further lateral growth of the reef and to the build-up of
its submerged parts.
Table 1.6. Annual rates and depths of erosion of reef-fiat
rock surfaces in the intertidal zone; data by Davies (1983);
Riitzler (1975), Trudgill (1976), Hudson (1977), Bromley
(1978)
Location
Florida
Bikini atoll
Bermuda
Australia
GBR of Australia
Aldabra atoll (upper part of
intertidal zone)
Same, medium part
Same, lower part
3-13
1
2.4-7.0
1-2
0.4-6.0
1.3-9.0
2.2-2.6
1.1-4.4
Depth (mm)
1.5-6.0
0.5
1.2
0.5-1
0.2-2.9
0.6-4.0
1-3
0.5-2.0
27
Among the most common benthic reef borers there should be mentioned
the sponges Ciiona, Anthosigmella, Siphonodyction, the bivalves
Lithophaga,
Gastrochaena,
Petricola,
the
vermetid
gastropods
Dendropoma, the sipunculid worms Phascolosoma, the polychaetes Eunice
(miticulata), Polydora, Fabricinus, Hypiscomus (elegans), the barnacles
Lithophrya (dorsalis), and the urchins Echinometra. On reef flats off the
Virgin Islands, in a zone covered by coralline algae, they are active over
30% of their total surface, thus furthering their destruction by surf (Adey
1975; Bak 1989).
An approximate estimate of the rate of erosion of reef-flat rock gives its
annual value as up to several kg m -2 (Table 1.6). Alone the boring sponges
in places of infestation may destroy 7-20kgm- 2 year- 1 of solid reef rock,
which could be much more than the possible calcification rate. Average
rates of bioerosion were evaluated to be within 0.4 kg m -2 (Stearn et al.
1977). The share of bioerosion comprises about two thirds of the total
(Trudgill 1976).
The mass of carbonate material produced by the erosion of reef into
rubble and sand is transported by surf and currents and also by migrating
animals (mainly by fish) ingesting the lime material to other zones of the
reef. So the bioerosion of solid reef rocks is one of the main sources of
formation of soft reef sediments (Stearn et al. 1977; Davies 1983). The
reef-flat of modern reefs, whose vertical growth was stopped by the recent
stabilization of the sea-level, became the zone of intensive production of
friable lime material. Transferred out to the leeward side of the reef it is
contributing to the further lateral growth of the reef and to the build-up of
its submerged parts.