Seed Production Patterns in Zostera marina: Effects of Patch Size and Landscape Configuration

Zostera marina is a cosmopolitan, temperate seagrass species capable of both sexual and asexual (i.e., clonal) reproduction. Until recently, the importance of sexual reproduction has been largely dismissed, and clonal growth has dominated our understanding of space acquisition by Z. marina. This model of Z. marina growth was developed in locations where reproductive effort falls on the lower end of a wide range in sexual productivity. This study assessed Z. marina seed production as a function of patch size in a landscape where sexual reproduction has played a significant role in meadow expansion. Additionally, a landscape-scale analysis of seagrass proximity was performed to determine whether relationships between seed production and percent seagrass coverage exist. Reproductive shoots were collected from 58 seagrass patches of four different size classes: 2.5, 5, 10, and 20 m² over a two-year period. Seeds were harvested, enumerated, and scored for viability. Viable seed density was significantly related to patch size, but no statistically significant difference was found for non-viable seed densities between patch sizes. Larger patches, with both an edge and center region, were evaluated by region; no difference was found between seed production at the edge vs. center for these size classes. Finally, seed densities were not positively correlated with the amount of proximate seagrass in the landscape. The results of this study suggest that more explicit regional studies of sexual reproduction dynamics must be undertaken to fully understand the complex reproductive ecology of this angiosperm.