Mangroves

Mangroves are pretty fantastic.  They have adaptations that allow them to live in saltwater. They exhibit vivipary, i.e. the seeds germinate while still on the plant and the propagules fall into the water as fully formed seedlings. They keep the coastline from eroding away. They provide a unique habitat for scores of animals. By trapping sediments in the roots, they actually make new land (a useful characteristic given rising sea levels). Unfortunately, mangrove ecosystems throughout the world are being decimated by coastal development. Go here or here for more about the currently dire situation with mangroves. 

Vieques still has some beautiful stands of red mangrove (Rhizophora mangle  L.), and slight trails have been cut through some of these so that you can skim through in a kayak. Which is how I got this video. [NOTE: The lovely bird hopping through the thicket of mangrove roots (starting at 0:34) is a green heron (Butorides virescens L.).]