NMFS is issuing a final rule determining Johnson's seagrass (Halophila johnsonii) to be a threatened species pursuant to the Endangered Species Act (ESA) of 1973, as amended, which means it is likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range. Johnson's seagrass is rare and exhibits one of the most limited geographic distributions of any seagrass. Within its limited range (lagoons on the east coast of Florida from Sebastian Inlet to central Biscayne Bay), it is one of the least abundant species. Because of its limited reproductive capacity (apparently only asexual) and limited energy storage capacity (small root-rhizome structure and high biomass turnover), it is less likely to be able to repopulate an area when lost due to anthropogenic or natural disturbances. NMFS will soon issue protective regulations under section 4(d) of the ESA for this species.