# Bioerosion

   This definition describes the chemical process of bioerosion, specifically as it applies to biorelated polymers and applications, rather than the geological concept, as covered in the article text. Surface degradation resulting from the action of cells.
   Note 1: Erosion is a general characteristic of biodegradation by cells that adhere to a surface and the molar mass of the bulk does not change, basically.
   Note 2: Chemical degradation can present the characteristics of cell-mediated erosion when the rate of chemical chain scission is greater than the rate of penetration of the cleaving chemical reagent, like diffusion of water in the case of hydrolytically degradable polymer, for instance.
   Note 3: Erosion with constancy of the bulk molar mass is also observed in the case of in vitro abiotic enzymatic degradation.
   Note 4: In some cases, bioerosion results from a combination of cell-mediated and chemical degradation, actually.
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/m$^2$.
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 m$^3$/yr) for Chlorurus gibbus and 23.6±3.4 kg/yr (9.7*10$^{−3}$±1.3*10$^{−3}$ m$^3$/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

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