bioerosion

Bioerosion describes the breakdown 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, acrothoracican barnacles 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. In one study, bioerosion of coral reef aragonite by an individual parrotfish was estimated to occur at a rate of 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 m³/yr) for '' Chlorurus sordidus''.

Bioerosion is also well known in the fossil record on shells and hardgrounds, with traces of this activity stretching back well into the Precambrian. Macrobioerosion, which produces borings visible to the naked eye, shows two distinct evolutionary radiations. One was in the Middle Ordovician (the Ordovician Bioerosion Revolution) and the other in the Jurassic. Microbioerosion also has a long fossil record and its own radiations.

Gallery

Image:LibertyBorings.jpg, '' Trypanites'' borings in an Upper Ordovician hardground, southeastern Indiana.
Image:Petroxestes_borings_Ordovician.jpg, '' Petroxestes'' borings in an Upper Ordovician hardground, southern Ohio.
Image:CarmelHdgd.jpg, '' Gastrochaenolites'' borings in a Middle Jurassic hardground, southern Utah.
Image:FaringdonCobble.JPG, Numerous borings in a Cretaceous cobble, Faringdon, England.
Image:JurRockgd01.jpg, Cross-section of a Jurassic rockground; borings include ''Gastrochaenolites'' (some with boring bivalves in place) and ''Trypanites''; Mendip Hills, England; scale bar = 1 cm.
Image:Teredolites.jpg, '' Teredolites'' borings in a modern wharf piling; the work of bivalves known as " shipworms".
Image:OrdHdgd03.jpg, Ordovician hardground cross-section with ''Trypanites'' borings filled with dolomite; southern Ohio.
Image:GastrochaenolitesMatmor.jpg, ''Gastrochaenolites'' boring in a recrystallized scleractinian coral, Matmor Formation (Middle Jurassic) of southern Israel.
Image:Osprioneides_kampto1.jpg, '' Osprioneides'' borings in a Silurian stromatoporoid from Saaremaa, Estonia.
Image:Gnathichnus Cenomanian 020413.JPG, '' Gnathichnus pentax'' echinoid trace fossil on an oyster from the Cenomanian of Hamakhtesh Hagadol, southern Israel.
Image:Geopetal Structure.jpg, Geopetal structure in bivalve boring in coral; bivalve shell visible; Matmor Formation (Middle Jurassic), southern Israel.
Image:Bioeroded brown bodies large.jpg, Borings in an Upper Ordovician bryozoan, Bellevue Formation, northern Kentucky; polished cross-section.

See also

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* Marine biogenic calcification

References

Further reading

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External links

Bioerosion Website
at The College of Wooster

{{Authority control

Erosion
Biogeomorphology