EPA's Vessel General Permit and Small Vessel General

occurrence over relatively short time frames (Virnstein et al. 2009). Due to this species’
physiology, low capacity for storage, and shallow root system, growth over large unsuitable
patches may be unlikely, and its ability to recover from widespread habitat loss may be limited.
Status and trends
On September 14, 1998, Johnson's seagrass was listed as threatened under the ESA (69 FR
49035).
Historical abundance estimates of Johnson’s seagrass are not available due to the species having
only recently been differentiated. Limited data indicate no large distributional gaps or changes
in abundance over much of Johnson’s seagrass distribution from 1994 to 1999. However, recent
increases in reported occurrence could be an artifact of recent increases in search efforts.
Natural threats
Storms can easily uproot or rip apart individuals and seagrass beds. Although this can serve to
disperse individuals into new habitats, it can also disturb established meadows. Subsequent
siltation following high turbidity events can also bury individuals or parts of plants.
Anthropogenic threats
Due to its delicate morphology, endemic range, lack of genetic diversity and a physiology ill
equipped to hold space and compete with other seagrasses, Johnson’s seagrass is vulnerable to
prolonged widespread human-induced disturbance and habitat loss and its potential for recovery
may be limited. Johnson’s seagrass and its habitat are threatened by several natural and
anthropogenic factors, including (1) dredging and filling, (2) construction and shading from in-
and overwater structures, (3) boat propeller and anchor scarring, (4) trampling, (5) altered water
quality (such as stormwater runoff and turbidity), and (6) siltation, as well as multiple deterious
effects of climate change (Waycott et al. 2009).
Critical habitat
Critical habitat for Johnson’s seagrass was designated on April 5, 2000 (65 FR 17786) and
includes (1) locations with populations that have persisted for 10 years; (2) locations with
persistent flowering populations; (3) locations at the northern and southern range limits of the
species; (4) locations with unique genetic diversity; and (5) locations with a documented high
abundance of Johnson’s seagrass compared to other areas in the species’ range. These PCEs are
critical to the conservation of the species because they protect persistently reproductive and
genetically diverse populations, allow for protective buffers along the distribution limits (i.e.,
edges of survival), and protect regions of high density that without further knowledge of species
biology, appear to serve the needs of Johnson’s seagrass. Ten regions of sheltered bay and inlet
waters are designated, including north and south of Sebastian Inlet, near Fort Pierce Inlet, north
of St. Lucie Inlet, a portion of Hobe Sound, the southern side of Jupiter Inlet, Lake Worth
Lagoon (north of Bingham Island and Boynton Inlet), waters of Lake Wyman, and wide areas of
northern Biscayne Bay. These regions occupy approximately 22,574 acres or 9,139 hectares.
Simply the nature of Johnson’s seagrass critical habitat makes it variable and prone to change.
The growth of boating in Florida and development of coastal areas has resulted in trampling,
propeller scarring, dredging, filling, shading, and altered water quality that has degraded these
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