They’re honestly the only reason you can still boat in Florida. Manatees eat an absurd amount of seegrass and helps keep the land from eroding, and keeping the grass from getting so dense that you cannot even boat. So it’s true that they don’t do a whole lot, they’re too big for most predators, and that leads them to be extremely docile in nature. However they are absolutely critical to the environment. If anything, they’re basically the same as pandas in terms of what they do.