We established a long-term monitoring program in pristine coral reef environments, targeting soft-bottom polychaetes as indicators of natural changes in their biodiversity patterns. This study allowed us to gather base-line information of richness, abundance and spatial-temporal variations of macrofaunal polychaetes, and associate these with sediment reef variables. Two sampling campaigns/year were conducted at seven stations, from 2009-2013. Sediment samples were collected near colonies of Orbicella faveolata. In the laboratory, macrofaunal samples were sieved, sorted, and preserved in Ethanol (70%). Sediment parameters were studied following standard laboratory protocols. All reef sediments had high content of sand and CaCO3 (80-85%), which is typical for reef-type sediments. This long-term study showed that the benthic macrofauna and polychaetes associated with sediments exhibit high biodiversity, and richness but low-density values, which vary in space and time, but no seasonality. A total of 5,349 individuals belonging to 27 taxonomic groups were collected. From those, Polychaetes (representing 18%) where analyzed in further detail. 980 specimens, from 69 species (31 families) were analyzed, from which 17 are new records for Venezuela. Two families presented the highest richness and abundance: Spionidae and Syllidae (6spp, 28%, and 7 spp., 9% respectively). In terms of abundance, the spionids Prionospio sp. and Prionospio cristata were the dominant species. A significant decrease in richness and abundance of polychaetes was recorded in April-2012. Likewise, organic carbon values decreased after April-2012. These variations suggest an important change in these environments that was reflected in the polychaete community in all locations.
