Gray's Reef National Marine Sanctuary
Gray's Reef National Marine Sanctuary
Cannonball Jelly Resource Protection

SoundScapes *

Discovering a New Dimension of the Reef

Gray's Reef live bottom

Gray's Reef live bottom.
Photo: Greg McFall, NOAA.

Gray's Reef is a vibrant live-bottom reef located approximately 16 miles east of Sapelo Island, Georgia. Given its remote location, most people experience Gray's Reef through pictures or videos showing some of the colorful fish and benthic organisms. However, anyone who dives there knows that there are many sounds associated with all the activity at Gray's Reef. Recently, NOAA and the University of Georgia have begun collecting recordings of ambient and human-caused sounds. A hydrophone has been deployed on the seafloor to record reef sounds within Gray's Reef. These recordings will be used to identify biological activity and potentially detect changes in the reef health.

Sound travels about four times faster in water than in air and can be heard from a great distance. Every day, humans generate considerable noise that can affect marine life. At Gray's Reef, marine vessels (click to listen) generate the majority of the anthropogenic sound. However, even the anchor chain for the GRNMS data buoy can be faintly heard from over a mile away, gently groaning as it rocks in the waves.

Scuba divers can experience some of the natural reef sounds in the water, but not all (many of the sounds are too faint for the human ear to detect without amplification). A large part of the ambient reef sounds are generated by snapping shrimp (click to listen) which can sound much like bacon frying. Tiny shrimp make a snapping sound to stun their prey long enough for the shrimp to catch them.

Fish can also grunt (click to listen) to warn off intruders from territorial waters. Unlike the snapping sound that the shrimp make which is loud, but very brief, the fish grunt is a low guttural sound that builds in intensity and then fades. In this sound clip, the grunt can be heard about 2 seconds into the recording. Listen carefully as the sound of the snapping shrimp briefly give way to the fish grunting.

Diver deployed hydrophone

Diver deployed hydrophone.
Photo: Dr. Scott Noakes, UGA.

These investigations into the world of sounds in the marine environment have opened a new dimension of Gray's Reef and other National Marine Sanctuaries. The Office of National Marine Sanctuaries (ONMS) has pulled together a team of staff and experts to collaborate on system-wide projects, including the recording in Gray's Reef. What we learn by listening in sanctuaries helps us address both a better understanding of the role sound plays in a natural marine environment and the potential effects of human-caused sounds. In addition, NOAA is currently developing an Ocean Noise Strategy that incorporates the importance of managing the soundscape of marine animals in places such as National Marine Sanctuaries using a comprehensive, agency-wide approach.

Data plot of reef sounds at GRNMS

Data plot of reef sounds at GRNMS. Researchers will be analyzing these recordings to try to understand the "soundscape" of Gray's Reef. The plot shows the individual clicks made by the shrimp which constitutes the majority of the ambient reef sounds. The area highlighted in blue shows one of many fish grunts recorded at GRNMS. Click image for larger view.
Image: Dr. Scott Noakes, UGA.

* The sounds heard in a particular location, considered as a whole.

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