Genetic diversity and gene flow in Zostera marina populations surrounding Long Island, New York, USA: No evidence of inbreeding, genetic degradation or population isolation

•No evidence of genetic degradation for eelgrass in Long Island waters was found.•Of 293 ramets analyzed, nearly all (n=278) were genetically unique individuals.•Clonal diversity ranged between 0.89 and 0.98 within the four Long Island estuaries.•No evidence of inbreeding was found.•Bayesian modeling could not assign individuals into distinct populations.