Sponge borings and encrusters on a modern bivalve shell, North Carolina.
describes the
erosion of hard
ocean substrates – and less often
terrestrial substrates – by living organisms. Marine bioerosion can be caused by
mollusks,
polychaete worms,
phoronids,
sponges,
crustaceans,
echinoids, and
fish; it can occur on
coastlines, on
coral reefs, and on
ships; its mechanisms include biotic boring, drilling, rasping, and scraping. On dry land, bioerosion is typically performed by
pioneer plants or plant-like organisms such as
lichen, and mostly chemical (e.g. by
acidic secretions on
limestone) or mechanical (e.g. by
roots growing into cracks) in nature.
Bioerosion of coral reefs generates the fine and white
coral sand characteristic of tropical islands. The coral is converted to sand by internal bioeroders such as
algae,
fungi,
bacteria (microborers) and
sponges (Clionaidae),
bivalves (including
Lithophaga),
sipunculans, polychaetes and
phoronids, generating extremely fine sediment with diameters of 10 to 100 micrometres. External bioeroders include
sea urchins (such as
Diadema) and
chitons. These forces in concert produce a great deal of erosion.
Sea urchin erosion of
calcium carbonate has been reported in some reefs at annual rates exceeding 20 kg/m².
Fish also erode coral while eating
algae.
Parrotfish cause a great deal of bioerosion using well developed jaw muscles, tooth armature, and a pharyngeal mill, to grind ingested material into sand-sized particles. Bioerosion of
coral reef aragonite by parrotfish can range from 1017.7±186.3 kg/yr (0.41±0.07 m³/yr) for
Chlorurus gibbus and 23.6±3.4 kg/yr (9.7 10-³±1.3 10-³ m²/yr) for
Chlorurus sordidus (Bellwood, 1995).
Bioerosion is also well known in the
fossil record on shells and
hardgrounds (Bromley, 1970), with traces of this activity stretching back well into the
Precambrian (Taylor & Wilson, 2003). Macrobioerosion, which produces borings visible to the naked eye, shows two distinct
evolutionary radiations. One was in the Middle
Ordovician (the Ordovician Bioerosion Revolution; see Wilson & Palmer, 2006) and the other in the
Jurassic (see Taylor & Wilson, 2003; Bromley, 2004; Wilson, 2007). Microbioerosion also has a long fossil record and its own radiations (see Glaub & Vogel, 2004; Glaub et al., 2007).
See also
