Abstract We studied the removal,of dissolved organic carbon,(DOC) by coral cavities of 50–250 dm,1 (Berau area). The net DOC removal,per square meter of cryptic surface likely exceeded,the gross primary,production,per square meter of planar reef area. We conclude,that coral cavities and,their biota are net sinks of DOC and,play an important,role in the energy budget,of coral reefs. Coral cavities are among,the largest and,least-known habitats in coral reef environments.,Their total volume comprises,up to two-thirds of the reef volume,(Garret et al. 1971; Ginsburg 1983) and their inner surface represents 60– 75% of the total available surface of the reef (e.g., Jackson et al. 1971; Logan et al. 1984; Scheffers 2005). Yet, hardly anything,is known,about the ecological role of this cryptic habitat in the carbon,cycling on the reef. The relatively sheltered cryptic habitat is inhabited,by a high abundance of different organisms, called cavity dwellers or coelobites (Ginsburg and Schroeder 1973). The biomass,of this cryptofaunal,community,might exceed that of the reef surface (Hutchings 1974; Brock and Brock 1977; Meesters et al. 1991) and,the encrusting,biota can cover