Fauna associated with coral reefs is mainly comprised of macroinvertebrates, yet characterization of their assemblages, and particularly of their size spectrum, remains largely unknown. During this research three attributes of the macrofauna community associated with coral formations of La Azufrada reef (Isla Gorgona, Colombian Pacific) were assessed: density, biomass, and community structure. Samples were taken from live coralline substrates (Pocillopora spp.), and inert coralline substrates, and macrofauna were sorted into five size groups: 0.5-1mm, 1-2mm, 2-4mm, 4-8mm, >8mm. In live coralline substrates, macrofauna biomass was remarkably higher, and it was mainly allocated in particular taxa (decapods symbionts of Pocillopora) and size groups (>8mm). Although no significant differences were found in macrofauna densities between live and inert coralline substrates, differences were found among size groups. Density allocation was more homogeneously distributed in live than inert coralline substrates. The importance of Crustaceans is also remarkable as it was the most dominant taxa. However, the strong correlation of different crustacean orders (Caridea and Tanaidacea) to a specific coralline substrate, explain the high dissimilarity found in macrofauna composition between substrates. Therefore, transitions from live to inert coralline substrates could lead to macrofaunal assemblages with remarkably lower organic matter contributions, and higher proportions of smaller crustacean macroinvertebrates (<1mm).
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