ABSTRACT: The small-scale distributions of chlorophyll a (chl a), pheopigments, oxygen and currents were determined in horizontal sections between coral reef cavities and benthic boundary layer waters (BBL) to estimate rates of grazing andrespiration by cryptic cavity-dwelling (coelobite) suspension feeders. We investigated 0.5 to 5 m long and 0.1 to 1 m wide cavities in fringing reefs on the western coast of the Gulf of Aqaba (Red Sea), between 2 and 16 m depth. Within cavities netcurrents averaged 0.9 cm s^-1, or 22% of the current speed measured in BBL ~2 m away from the reef. In spite of rapid flushing of cavity waters within a few minutes, we encountered significant chl a and oxygen depletions relative to BBL,particularly under oligotrophic conditions. Chl a depletions amounted, on average, to 0.10 ± 0.03 mg m^-3 (median ± median absolute deviation [MAD]) or 54% (max. 86%) of BBL values and showed a positive relation to coelobite suspensionfeeder densities. Pheopigments, by contrast, remained remarkably constant, indicating selective grazing of the mainly picoplankton-sized food. Oxygen depletions were weak and mainly related to flushing. In sack-shaped cavities they amounted to 13.6 ± 6.1mmol m^-3 or 3 to 9% of BBL concentrations. Analyses of water flow and chl a distributions show that under oligotrophic summer conditions 0.7 g C m^-2 d^-1 of phytoplankton disappears within the upper 1 m of cavernousreef framework. This conservative estimate is about 1 order of magnitude higher than grazing rates of coral-dominated communities on the exposed reef, rendering cryptofauna suspension feeding an important and new pathway of extrinsic organic matter intocoral reefs.