Allozymic implications of the propagation of eelgrass Zostera japonica within a river system

We examined the allozymic variation of Zostera japonica, a seagrass in brackish-water zones, for plant samples collected from the Ohashi River (four localities including nine sampling sites within 7.5km) and Lake Nakaumi (one location), to which it is connected, in Japan to study plant propagation. Among five enzymes detected, phosphoglucoisomerase (PGI) showed three alleles (b, c, d) and five genotypes (bb, cc, dd, bd, cd), but the other four enzymes were monomorphic in 185 plant samples. PGI genotype variation was found not only in large meadows but also in small (< 1 m) vegetation patches, indicating genet coexistence within a small spatial scale. The observed genotype frequencies in large meadows did not differ significantly from Hardy-Weinberg equilibrium. However, no plant sample included genotype be. These results suggest that new genet recruitment by mating among genets has occurred but that recruitment may not be very frequent. The allele frequencies differed significantly, not only between distant (1.4km) meadows but also within short distances (20-40m) within a meadow. Plants carrying allele c were collected from the upper but not from the lower part of the Ohashi River. These results suggest successful dispersal by water currents is restricted.