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Bioerosion describes the breakdown of hard ocean substrates – and less often terrestrial substrates – by living organisms. Marine bioerosion can be caused by , Polychaete, , sea sponge, crustaceans, Echinoderm, and fish; it can occur on , on , and on ; its mechanisms include biotic boring, drilling, rasping, and scraping. On dry land, bioerosion is typically performed by or plant-like organisms such as lichen, and mostly chemical (e.g. by acidic secretions on limestone) or mechanical (e.g. by 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 sea sponge (Clionaidae), (including Lithophaga), , polychaetes, Rogerella and , generating extremely fine sediment with diameters of 10 to 100 micrometres. External bioeroders include (such as Diadema) and . 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 , 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==
borings in an Upper Ordovician hardground, southeastern Indiana.]] borings in an Upper Ordovician hardground, southern Ohio.]] hardground, southern Utah.]] in place) and Trypanites; Mendip Hills, England; scale bar = 1 cm.]] hardground cross-section with Trypanites borings filled with dolomite; southern Ohio.]]'' echinoid trace fossil on an oyster from the Cenomanian of Hamakhtesh Hagadol, southern Israel.]]
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