SPECIES DISTRIBUTION 



Johnson's seagrass is found in disjunct and patchy distribution along the east coast of Florida 

 from central Biscayne Bay to Sebastian Inlet, The largest patches have been documented inside 

 Lake Worth Inlet. The southernmost distribution is reported to be in the vicinity of Virginia Key 

 in Biscayne Bay. The species has been found in coarse sand and muddy substrates and in areas 

 of turbid waters and hiyh tidal currents. 



MAJOR IMPACTS 



Johnson's seagrass is the rarest species of its genus, has limited distributional characteristics, 

 restricted reproductive capacity (being asexual), and is dependent on substrate stability. Potential 

 for continued existence and recover^' may be limited due to habitat alteration by a number of 

 human and natural perturbations. Such perturbations include ( I ) prop scoring. (2) dredging, (3) 

 storm action, (4) siltation and (5) altered water quality. 



Alteration and subsequent destruction of the benthic community due to boating activities, 

 propeller scoring and anchor mooring has been observed in Johnson's seagrass sites. Such 

 activities result in breaking root systems, severing rhizomes and significantly reducing the 

 physical stability of this ecosystem. Dredging redistributes sediments, buries plants and destroys 

 bottom topography. Some abundant populations are located in close proximity to inlets, and are 

 likely to experience erosional forces and siltation associated with severe storms. During 

 hurricanes, storm surge may scour and redistribute sediments, thereby eroding or burying 

 existing populations. 



Siltation due to human disturbance and increased land-use can also threaten viability of the 

 species. Degradation of water quality due to human impact is also a threat to the viability of 

 ecologically important seagrass communities. Nutrient over enrichment, caused by inorganic 

 and organic nitrogen and phosphorus loading via urban and agricultural land run-off, can 

 stimulate increased algal growth that may smother Johnson's seagrass by shading rooted 

 vegetation and diminish the oxygen content of the water. 



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