Introduction
Bioerosion denotes the biological breakdown of hard substrates—predominantly in marine settings but also on land—by organisms that bore, drill, rasp, scrape or otherwise remove material from coastlines, reefs, vessels and other rigid surfaces. At the microscale this process can be framed as cell‑driven surface degradation: activity of colonizing cells alters or removes surface layers often without changing the bulk molar mass of the substrate. Such degradation may be mediated directly by cellular activity, by chemical chain‑scission reactions, or by a combination of both when chemical cleavage outstrips the penetration of reagents (for example, diffusion of water into hydrolytically labile polymers); analogous behavior has been observed in abiotic, enzymatic degradation experiments in vitro.
Marine bioeroders span a broad taxonomic spectrum and employ diverse mechanical and biochemical modes of destruction. Macroborers and internal eroders—microalgae, fungi and bacteria (microborers), sponges (notably Clionaidae), boring bivalves (e.g., Lithophaga), sipunculans, polychaetes, acrothoracican barnacles and phoronids—work within reef frameworks and carbonate skeletons, reducing carbonate structures to very fine particles (typical diameters 10–100 μm) that are a major source of the fine white sands characteristic of many tropical islands. External grazers such as echinoids and chitons remove exposed carbonate by abrasion; grazing sea urchins (for example Diadema spp.) have been reported to erode calcium carbonate on some reefs at localized annual rates in excess of 20 kg m−2. Fishes, particularly parrotfishes, contribute substantial bioerosion while cropping algal turf: their robust jaws, tooth plates and pharyngeal mills grind ingested material into sand‑sized fragments. Measured individual bioerosion rates illustrate this impact—e.g., Chlorurus gibbus ~1017.7 ± 186.3 kg yr−1 (≈0.41 ± 0.07 m3 yr−1) and Chlorurus sordidus ~23.6 ± 3.4 kg yr−1 (≈9.7×10−3 ± 1.3×10−3 m3 yr−1) in one study.
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On land, bioerosion is typically initiated by pioneer organisms such as lichens and by vascular plants whose roots exploit fractures; the dominant mechanisms are chemical weathering (acidic secretions attacking calcareous rock) and mechanical wedging by roots, producing progressive surface breakdown and contributing to soil formation. Bioerosional activity is well represented through geological time: trace fossils of borings and other bioerosion extend into the Precambrian, with pronounced expansions of macrobioerosion in the Middle Ordovician (the Ordovician Bioerosion Revolution) and again in the Jurassic; microbioerosion likewise shows an extensive fossil record and its own radiations.
Contemporary examples, such as sponge borings (Entobia) and encrusting organisms on bivalve shells (e.g., documented localities in North Carolina), illustrate how sessile and boring taxa modify and degrade carbonate substrates in modern coastal environments, linking present‑day processes to long‑term sediment production and reef framework alteration.
The suite of illustrated specimens documents pervasive marine bioerosion from the Ordovician through the Recent across a range of shallow‑marine substrates and paleogeographic settings. Ordovician hardgrounds and skeletal substrates from the U.S. Midwest (southeastern Indiana, southern Ohio, and northern Kentucky) preserve shallow, tool‑mark and microborings such as Trypanites and Petroxestes, including cross‑sections showing dolomite‑infilling of Trypanites and borings penetrating bryozoan skeletons—evidence for early diagenetic mineralization of cavities and extensive bioerosional penetration of colonial organisms. Jurassic examples from the western and southwestern United Kingdom and southern Utah illustrate the co‑occurrence of microborings and larger enlargement‑type borings (Trypanites and Gastrochaenolites), with some Gastrochaenolites specimens retaining boring bivalves in life position and photographic scales (1 cm) revealing fine‑scale relationships between macro‑ and microborings in rockgrounds. Middle Jurassic reefal carbonates of southern Israel (Matmor Formation) preserve Gastrochaenolites and associated bivalve borings that retain geopetal indicators and the occupying shells, linking boring behavior to subsequent depositional history and taphonomy. Palaeozoic and Mesozoic examples elsewhere include large, elongate Osprioneides borings in a Silurian stromatoporoid from Saaremaa (Estonia) and intensive cobble borings from Cretaceous nearshore deposits at Faringdon (England), demonstrating the breadth of host types exploited by borers. Modern Teredolites in wharf timbers (shipworms) provide a present‑day analogue for wood bioerosion, while grazing traces such as the echinoid Gnathichnus pentax on a Cenomanian oyster from southern Israel record non‑boring surface modification. Collectively, these gallery specimens highlight taxonomic, behavioral and taphonomic diversity in marine bioerosion, illustrating how borings, their infills, and infaunal occupants inform interpretations of paleoecology, substrate use, and early diagenetic processes.