Around intertidal coral reefs, viscous layers, flocs, and bubbles can form on the water surface, and these are collectively referred to as mucus aggregates. To assess effects of substances contained in mucus aggregates on population growth rates of autotrophic and heterotrophic organisms, aqueous materials extracted from mucus aggregates and polysaccharides collected from cultured microalgae were added to rocky intertidal reef sediments in a controlled laboratory experiment. Temporal changes in autofluorescence cell density and nonautoflorescence cell density in reef sediments were examined. Results suggested that microorganism population growth in subtropical rocky intertidal reefs is limited by low concentrations of organic carbon and nutrients in the environment, and that components of mucus aggregates can supplement these materials, leading to increased microbial population growth rates. In particular, aqueous extracts of mucus aggregates contained nutrients that likely promoted growth of autotrophic bacteria, whereas extracellular polymeric substances (EPS) contained polysaccharides that likely promoted growth of heterotrophic bacteria.