Hutchings and Hoegh-Guldberg, 2008:

"Biological erosion consists of the loss of reef substratum by boring and by grazing. A suite of organisms including polychaetes, molluscs, sponges, barnacles, sipunculans, and various micro-organisms such as bacteria and algae bore into coral substrata. Endolithic algae colonise the skeletons of corals (Fig. 8.2A) that colonise the surface layers of the substratum together with the turf algae (Fig. 8.2B). Algae is grazed by fish (Fig. 8.2C, D) as well as invertebrate grazers such as chitons (Fig. 8.2E), echinoids (Figs 8.2F, G; 26.8A–F), and gastropods (Fig. 8.2H). These organisms physically bite or scrape the substratum to collect the algae (Fig. 8.3A) and with it they take particles of the substratum that has become honeycombed by the action of the borers (Fig. 8.3B). This calcium carbonate matrix, together with the algae, passes through the gut of the grazers and is ground up, separating the algae from the calcium carbonate. Cellulose enzymes break down the plant cells, the nutrients are then absorbed, and then the calcium carbonate is defecated as a fine powder. Swimming behind large schools of parrotfish (scarids, Fig. 8.3C) one often sees the water column becoming cloudy as this fine powder is ejected (Fig. 8.3D). Similarly the faecal pellets of grazing echinoids consist largely of compacted finely ground calcium carbonate. The lagoonal sediments, especially those offshore, are largely composed of these products of bioerosion and physical erosion—along with mollusc shells, carapaces of crustaceans, foraminifera tests and sponge spicules. Only sediments adjacent to the coast or large islands have a component of terrestrially derived sediments."

AND

"As human populations have expanded in the coastal areas of tropical and subtropical oceans their influence on the environment that surrounds coral reefs has increased dramatically. Changes to the nutrient and sediment concentration of the waters surrounding corals have impacted the growth and calcification of a wide range of organisms. In the last two decades, these local impacts have been joined by global factors such as global warming and ocean acidification (see Chapters 9 and 10). Together, local and global factors have decreased the growth in calcification of reefs while at the same time probably increasing the rate of dissolution and/or bioerosion. These changes are complex and interactive, and have far-reaching consequences for both natural ecosystems and the human societies that depend on them."

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Citation and/or URL

Hutchings, P. & Hoegh-Guldberg, O. 2008, Calcification, erosion and the establishment of the framework of coral reefs, In The Great Barrier Reef: biology, environment and management, eds. P. Hutchings, O. Hoegh-Guldberg & M. Kingsford, CSIRO Publishing, Collingwood, Australia.  © ACRS 2008.  http://www.publish.csiro.au/pid/5921.htm

Spatial Coverage

Great Barrier Reef 

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Not applicable

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