The number of manatees in Florida has increased greatly since they
were protected, so the question is whether
to designate
them as "threatened" rather than "endangered".
A species can't survive if its habitat is wiped out. The US often
protects one endearing endangered species as a way of protecting the
whole ecosystem, including many other species, that it lives in. It
seems that manatees are an example of this. The existing restrictions
enable manatees to coexist with human water activities, but this
redesignation would permit land development that could wipe out all of
them.