Reef carbonate budget

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The accounting identity that decides whether a reef is a structure or a ruin. Gross carbonate production — chiefly coral calcification, with coralline algae cementing the framework — is set against gross removal: physical erosion by waves, chemical dissolution, and bioerosion by organisms that bore, scrape and excavate the substrate. Parrotfish, urchins, boring sponges and bivalves are all on the removal side. A reef with a net positive budget accretes and can keep pace with rising sea level; a reef with a net negative budget loses relief and complexity even while living coral is still present on it. This is the frame in which a reader should understand bleaching: a mass mortality event does not just remove coral, it flips the sign of the budget, because the removal side keeps running at full rate while the production side stops.

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