Conversation so far:
where are the most highly productive tropical marine ecosystems found
Mangrove swamps are generally highly productive tropical marine ecosystems.
where are the mangrove swamps found in north america
In North America, mangrove swamps are found from the southern tip of Florida along the Gulf Coast to Texas.
how many species of mangrove trees are there in the us
Only four species of mangrove trees are found in the United States: red, black, white, and buttonwood.

Question: how many species are there in the world
Self-contained rewrite: how many species of mangrove trees are there in the world