This 5-year review is a periodic analysis of Johnson's seagrass to ensure that the listing…
About the Species
Like other seagrasses, Johnson's seagrass plays a role in the health of "benthic" (anything associated with or occurring on the bottom of a body of water) resources as shelter and nursery habitat. Johnson's seagrass is the first—and only—marine plant species to be listed under the Endangered Species Act. It is listed as threatened.
Johnson’s seagrass is a small statured marine plant, growing to only 5 cm in height. It is capable of growing in the intertidal zone, on dynamic flood deltas inside ocean inlets, at the mouths of freshwater discharge canals, and subtidal waters to depths of approximately 3-4 meters; yet is only found within Florida’s intracoastal waters from Sebastian Inlet to Virginia Key in Biscayne Bay. This is the smallest geographic distribution of any seagrass worldwide. Within this range, it is among the least abundant seagrass species. It grows in small, sparse patches and may disappear from areas for months or years before reappearing. It can mix with other seagrasses though its short stature precludes it from dense stands of taller species as it is outcompeted for light resources. Johnson’s seagrass has a broader tolerance range for light, temperature, and salinity than congeners and seems capable of growing in suboptimal conditions where other species cannot survive.
Johnson’s seagrass is considered dioecious, which means each plant only contains the flowers of one sex (male or female). Interestingly, no individual Johnson’s seagrass plants have been found with male flowers. Similarly, researchers have not found any seedlings. Taken together, Johnson’s seagrass appears to reproduce only through vegetative fragmentation (asexual reproduction) and not through the development and dispersal of seeds (sexual reproduction). This strategy likely hinders its ability to expand in range or recolonize following disturbances.
Given Johnson’s seagrass’ unusual life history and its similarity to other Halophila seagrasses NOAA Fisheries and partners have been genetically researching the Halophila genus. Our scientists and partners use a variety of innovative techniques to study, learn more about, and protect this species.
ESA Proposed for Delisting
- Throughout Its Range
In the Spotlight
On December 23, 2021, we published a proposed rule to remove Johnson's seagrass (Halophila johnsonii) from the Threatened and Endangered Species Act. To correspond with this action, we are also proposing to remove the critical habitat designation for Johnson's seagrass. We propose these actions based on newly obtained genetic data that demonstrate that Johnson's seagrass is not a unique taxon but rather a clone of an Indo-Pacific species, Halophila ovalis.
Recovery Planning and Implementation
Species Recovery Contact
Adam Brame, Recovery Coordinator
Key Actions and Documents
Johnson's Seagrass may have the most limited distribution of any seagrass on earth, known to only…
Data & Maps
Tracks the implementation of recovery actions from Endangered Species Act (ESA) recovery plans.