Size structure of the macrofauna community associated with coral formations of La Azufrada reef (Isla Gorgona, Colombian Pacific)

Fauna associated with coral reefs is mainly comprised of macroinvertebrates, yet community structure of these organisms remains largely unknown. During this research three attributes of the macrofauna community associated with coral formations of La Azufrada reef (Gorgona Island, Colombian Pacific), were assessed: biomass (wet weight), density, and taxonomic composition (high taxonomic levels). Samples were taken from two substrates, live colonies of Pocillopora spp., and inert coralline substrate, and macrofauna were sorted into five size groups: 0.5-1mm, 1-2mm, 2-4mm, 4-8mm, >8mm. Macrofauna biomass in live colonies were almost 14 orders of magnitude greater than in inert substrates. These differences were much less noticeable when densities were compared, being higher in inert substrates. Biomass and density also behaved differently when size groups within the same substrate type were compared. In both substrates, >8mm groups were largely responsible for total biomass. This dominance pattern was also observed for density in inert substrates, where the smallest group (0.5-1mm) accounted for total values. In live colonies, however, contributions to total density were more balanced within groups. Taxa richness was higher in inert than in live colonies (n=25 vs. n=19, respectively). Nevertheless, both macrofauna communities were dominated by two crustacean groups, Tanaidacea (inert substrates) and Caridea (live colonies). This single taxa dominance pattern was also followed within size groups, being particularly outstanding in 4-8mm/>8mm inert substrate groups and in 1-2mm/2-4mm live substrate groups. Transitions from live to inert coralline substrates lead to macrofaunal assemblages with lower organic matter contributions, and higher proportions of smaller macroinvertebrates (<1mm).