Size and estimated age of genets in eelgrass, Zostera marina, assessed with microsatellite markers

We examined the spatial distribution of genotypes in a perennial population of eelgrass, Zostera marina L., at two spatial scales. We mapped and sampl ed 80 ramets in a subtidal area of 20 x 80 m, and an additional 15 ramets i n two 1-m(2) sub-quadrats. Ramets were genotyped for seven polymorphic micr osatellite loci. Among a total number of 54 genotypes detected, 12 occurred more than once. The ramets of ten of these genotypes occurred in clusters and represented genets based on their expected multi-locus genotype frequen cies. The size distribution of genets was uneven with estimated ramet numbe rs ranging from 2 to 5000. Whereas some areas displayed a high genet divers ity, which may indicate past disturbances, large genets (greater than or eq ual to 10 m(2)) predominated in other locations of the sampled plot. Spatia l heterogeneity in clone distribution was also obvious at the smaller sampl ing scale (15 ramets sam.. pled within m(2)) were the clonal diversity (gen ets identified/ramets sampled) was 0.24 in one quadrat, and 0.077 in the et her. Ramets belonging to the largest clone were maximally 17 In apart, whic h corresponds to a genet age of 67 yr based on annual rhizome growth rates. We conclude that the spatial arrangement of clones in seagrasses allows in ferences about the past demography and the disturbance regime at a given si te which may prove useful for coastal zone management of ecologically valua ble seagrass meadows.