People often think that the underwater world is silent. In fact, numerous marine organisms use sound for communication, reproduction, and to seek prey. Gray's Reef National Marine Sanctuary recently created an inventory of acoustically-active organisms in the sanctuary and discovered an impressive number of species that utilize sound in some way - including marine mammals, turtles, fish, and invertebrates. Recongizing that the soundscape is an important part of the habitat at Gray's Reef, we have deployed instruments like the one in this photo to record sounds in this not-so-silent world.