The seagrass meadows of Thalassia testudinum grasslands constitute one of the coastal environments with a great diversity of organisms and a high productivity. In order to study the polychaete community associated with Thalassia, monthly samplings were conducted in Mochima Bay from January to December 2002. Eight replicates were taken monthly at each site, using a 14.8 cm diameter PVC corer. Each core sample was sieved through a 1 mm mesh, and the polychaetes were preserved in 8% formalin solution. The polychaetes were fixed in an 8% formalin solution. A total of 2097 specimens were collected, identifying 94 species belonging to 31 families; the families Terebellidae, Serpulidae, Spionidae and Syllidae have the greatest number of species and together represent 40.42% of the total identified species. Mangle Quemao had the highest abundance and species richness, while Varadero had the lowest. The average diversity value was 2.14 ± 0.29. A PERMANOVA analysis revealed statistically significant differences in abundance across all considered sources of variation.
