Genetic diversity plays a seminal role in the dynamics of species invasions.  Native populations with greater diversity might better resist invasion, while genetic diversity of non-natives might render them more successful invaders and competitors.  The west coast of North America is home to two congeneric species of submerged aquatic angiosperms: native eelgrass (Zostera marina), and dwarf eelgrass (Zostera japonica), a rapidly-expanding invasive exotic.  We used population genetic measures to predict the past, present, and future dynamics of exotic/native interactions in this system.  A series of microsatellite markers were analyzed to estimate the genotypic and allelic diversity within 5 populations of dwarf and native eelgrass in Washington state. 

Results/Conclusions

Microsatellite diversity of native eelgrass varied greatly among sites, with all populations having greater than expected (P < 0.05) allelic diversity, heterozygosity, and outbreeding.  Genetic diversity of dwarf eelgrass was not as high as that of native eelgrass, but the presence of multiple clones suggested a) repeated plant introductions, and b) the possibility of this exotic’s spread into a broad range of inter- and subtidal habitats.  Finally, within a single location, genetic diversity of dwarf and native eelgrass were negatively correlated (P < 0.05).  Baseline data collected in this study are being used to construct a predictive model for the ongoing invasion trajectory of dwarf eelgrass.