Here is an article from USGS.gov regarding a study on this topic.
“With high numbers of manatees using the Florida Power and Light power plant warm water refuge during winter, their impact on the seagrass beds in the Indian River Lagoon is considered an important indicator of the long-term capacity of the area to support the manatees. USGS is working with partners to investigate the spatial extent and intensity of manatee use of seagrass beds in the area. ”
For more information click here.