Carbon fluxes of coral reefs

Abstract

Ranges, means, and limits of carbon metabolism are summarized for coral reefs worldwide; zones and habitats of carbon production and consumption are also described. The underlying functional processes and parameterizations of those processes are discussed. At this time, however, there are gaps in knowledge, and it is particularly noted that interactions with nutrients are not yet well established. Dissolved inorganic carbon (i.e., carbon dioxide gas, bicarbonate, and carbonate ion) is removed from the water column by autotrophs and fixed into organic (tissue and photosynthate) and inorganic (calcium carbonate skeletons) compounds. Gross primary production and community respiration rates vary greatly in different habitats of reefs, with much of the respiration of organic material occurring within the organism or the habitat in which it was produced. Net community production varies among habitats. In classic reef zonation, carbon from the fore-reef is exported to the back-reef area as detritus and dissolved organic carbon. Coral reef communities take up suspended planktonic organic matter at rates that are relatively low compared to their own primary production. Sediments in coral reefs typically contain <1% organic carbon, indicating little sequestration of organic carbon into these systems. Dissolution of calcium carbonate occurs naturally inside coral heads, in interior pore-spaces of coral reef sediments, and from the erosion action of boring organisms. Globally, the surface area of coral reefs is small and thus coral reefs have negligible effect on the global carbon cycle.