seagrass

Etymology

sea +‎ grass

Noun

seagrass (plural seagrasses)

1. Any of various grass-like marine plants that grow underwater in salt water.
   • 2007 October 2, Henry Fountain, “Wayward Youths (or Green Turtles) and Their Drifting Ways”, in New York Times‎:

     They are not seen again until they arrive as larger juveniles in shallow coastal waters, where they dine on seagrass and algae.