How clone can you go? Seedbank density and a multiscale assessment of genotypic diversity in the seagrass Halodule wrightii

Seagrass conservation and management plans are placing increasing emphasis on the collection of data related to seagrass bed “condition” such as vegetative characteristics, seed production and genetic diversity. One important aspect of genetic diversity in species that reproduce both sexually and asexually is genotypic diversity. Genotypic (clonal) diversity is usually described as the proportion of unique genets within a population (richness), but it can also be characterized in other ways such as the degree to which individual ramets are distributed among genets (evenness) or the spatial arrangement of genets relative to one another (architecture). Genotypic richness, evenness, and architecture have the potential to influence sexual reproduction by affecting the proximity of genets, a key feature in dioecious species where pollen dispersal is limited and clones can vary greatly in size. They may also differ substantially according to the scale at which they are measured. This study examined genotypic richness, evenness and architecture across multiple spatial scales in the seagrass Halodule wrightii, and its association with seedbank density from three sites in the northwest Gulf of Mexico. While the magnitude of diversity estimates differed, the overall patterns remained consistent across scales. Seedbank density ranged from 19 +/- 9 to 188 +/- 30 seeds m-2, following a gradient from north to south. The highest and most consistent production of seeds occurred at a site where richness (R: 0.24 - 0.42) and evenness (ED: 0.67 - 0.93) were uniformly high across spatial scales, and clonal architecture (Ac: 0.20 – 0.36) was represented by a high degree of intermingling.