Seed dispersal and burial are important processes in the expansion and restoration of Zostera marina (eelgrass). The depths at which seeds are buried are a significant factor contributing to seedling survival. If seeds are buried below 6 cm, it is unlikely that viable seedlings will develop. Burrowing behavior of infaunal organisms can contribute to seed burial and has the potential to be a positive or negative influence on seedling survival. In this study, a mesocosm experiment tested the relationship between lugworm (Abarenicola pacifica) density and eelgrass seed burial. Three treatments (no worms, low-density, and high-density of worms) were used to examine seed burial. Three replicates per treatment were seeded with a blend of mimics and real seeds. After 25 days, three cores were extracted from each replicate and the depths of the seeds were recorded. In the high-density worm treatments, the majority of the seeds and mimics were found buried below the 6 cm critical depth, while in the low-density treatment most were shallower than 6 cm, with most of the seeds in the control treatments remaining at the surface. These results indicate that the density of A. pacifica should be investigated in order to predict the success of Z. marina expansion and restoration efforts.