Polychaetes constitute an important group in soft-bottom marine ecosystems. This study evaluated the biological diversity of annelids in seagrass meadows and surrounding sandy bottoms in the Morrocoy National Park; spatial and temporal variation patterns; and associations with morphological/structural variables of the plant and sediment. Five locations were selected: three with greater continental influence and two with oceanic influence. Samples of benthic organisms were taken with suction and PVC cylinders in the seagrass meadows (ACV) and with dredges in surrounding sandy bottoms without vegetation (ASV) in 4 samplings carried out in the months of February, May, August and November of the year 2000. 67 species were identified, more abundant are Capitella cf. capitata (26.82%), Prionospio caribensis (13.22%), Streblospio gynobranchiata (7.42%) and Schistomeringos pectinata (6.6%). In the ACVs were observed: one group of spionids and capitellids, whose abundances increased in the month of February 2000 at localities with continental influence; and second of spionids, silids and dorvileids, with low and relatively constant densities throughout the year. The first group of opportunistic species, suggesting that these high densities in February are peak responses, followed by mortality and/or dispersion to other environments. In the ACV, espionid Streblospio gynobranchiata and the syllids Syllis lutea, S. bansei and S. prolifera, present a positive relationship with the foliar biomass of seagrass, while Capitella cf. capitata and Pseudopolydora with shoot density and rhizome/root biomass, possibly related to their infaunal habits. No defined spatio-temporal pattern was observed in the ASV and most species presented positive relationships with the content of organic matter and mud in the sediments, related to their feeding habits.
