The Research Area at Gray’s Reef

Snapshots of Science in the South Atlantic Bight

By Michelle Riley

March 2021

map of Gray's Reef National Marine Sanctuary

A Living Laboratory

Gray’s Reef National Marine Sanctuary is one of America’s most significant underwater places. The 22-square-mile sanctuary is teeming with marine life within a vibrant ecosystem. An excellent representative of live-bottom reefs along the Georgia and Carolina coasts, Gray’s Reef is the only protected natural reef -- not man made -- in the Atlantic Ocean between Cape Hatteras, North Carolina and Cape Canaveral, Florida. Scientists have identified more than 900 species of invertebrates (animals without a backbone) and more than 200 species of fish, in addition to loggerhead sea turtles and other animals. The habitats found at Gray’s Reef are essential to providing food, shelter, and reproductive opportunity for the creatures that live in and visit the sanctuary. Scientific research and monitoring are critical to informing sanctuary managers of the condition of these habitats.

Gray’s Reef National Marine Sanctuary released a report last year that reviews scientific research in and around the sanctuary’s dedicated research-only area from 2012 to 2016. The area, which NOAA established in 2011, is closed to fishing and diving, thereby creating a control site for scientists that is designed to minimize the effects of variables, including human activities – earning it the nickname, “living laboratory.”

Gray's Reef research area
Enlarged map with the research area indicated in red, covering the southern third of Gray’s Reef National Marine Sanctuary. Map created by Tony Reyer/NOAA

Cutting Edge Technology

A scientist from the Skidaway Institute of Oceanography, Dr. Catherine Edwards, deploys cutting-edge technology like gliders in Gray’s Reef to study fish migration patterns and to complement our stationary acoustic telemetry array. The gliders are a type of remotely operated vehicle that carry receivers that listen for tagged animals, and send a “ping” to let us know they are swimming in the sanctuary. Dr. Edwards’ work has found that the amount of vertical mixing in the water column, as well as tidal and wind-driven currents, determine how far the sound of each “ping” carries from the animal. As Dr. Edwards works to determine what factors affect the performance of these mobile acoustic arrays, measurements from the glider are used to estimate sound speed and predict how far each “ping” travels. This information helps sanctuary scientists interpret the data from the stationary acoustic array, and allows Dr. Edwards and her team to adapt the strategy the gliders use in Gray’s Reef in real time, based on how sound travels.

glider below the water as researchers look on from a boat
A team of marine researchers checks an ocean glider before releasing it into the ocean. Photo: Edmund Hughes/University of South Florida

Who’s Eating Whom for Dinner?

Scientists are studying predator-prey interaction throughout the water column. Research indicates that large predatory fish in the middle of the water column, such as Spanish mackerel and greater amberjack, chase small prey toward the bottom of the seafloor. This allows predators living near the bottom, such as black sea bass and scamp grouper, to jump up and eat the small prey fish. Scientists don’t yet know if the predators are working together or if it’s just a favorable occurrence for the grouper and sea bass. The project is led by Dr. Peter Auster of University of Connecticut and Mystic Aquarium, in partnership with NOAA and Coastal Carolina University.

scamp grouper
Scamp grouper (Mycteroperca phenax) at dusk approaching and stalking a school of prey in Gray’s Reef. Photo: Dr. Peter Auster, University of Connecticut/Mystic Aquarium

Here to Stay or Just Visiting?

In another project led by Dr. Auster, scientists use acoustic telemetry with tagged fish to assess movement patterns. So far, we’ve learned that black sea bass can stay in Gray’s Reef National Marine Sanctuary for well over a year, whereas gag and scamp grouper barely stay a month. This can help managers better understand predator-prey relationships and fish breeding and feeding strategies. If you go on an annual dive trip to Gray’s Reef, you might run into your old friend, Sam the black sea bass.

acoustic reciever underwater
An acoustic receiver is deployed to track tagged fish. Photo: Dr. Peter Auster, Mystic Aquarium/University of Connecticut

Prey Fish at Gray’s Reef

Gray’s Reef attracts more than 200 species of fish. Scientists from Swarthmore College, University of Connecticut, Mystic Aquarium, and NOAA learned that there is an abundance of prey fish at Gray’s Reef’s taller ledges. Prey fish, also known as forage fish, are an important component of the food web, and understanding patterns of their distribution and abundance can provide useful information about the larger reef community at Gray’s Reef. Tomtate, spottail pinfish, round scad, they’re all there. Care for anchovy on your pizza? Get it at Gray’s Reef!

Scad (Decapterus sp.) prey fish aggregate densely over a ledge. Photo: Dr. Peter Auster, Mystic Aquarium/University of Connecticut

Associations between fish and invertebrates

Just as clownfish live among sea anemones, lots of animals are found among the stony coral, Oculina arbuscula, in Gray’s Reef. Dr. Daniel Gleason of Georgia Southern University, Dr. Timothy Henkel, formerly of Valdosta State University, and Dr. Roldan Muñoz of NOAA, sought to discover whether or not that particular stony coral helped young fish survive and grow among hard-bottom reefs in the South Atlantic Bight. The scientists observed the tiny crested blenny and belted sandfish, purple sea urchins, snapping shrimp, coral clinging crabs, arrow crabs, and a variety of other animals among the coral branches. Although they found patterns of association, strong support for a link between Oculina arbuscula and fish recruitment was not supported by the data.

coral infront of diver's hands
The coral Oculina arbuscula is common at Gray's Reef and is an important habitat-forming species, providing good hiding places for small fish and invertebrates. Here, a scientist inspects a colony for the presence of the coral clinging crab Mithrax hispidus.

Benefits of Research at Gray’s Reef

As a living laboratory, Gray’s Reef serves as a catalyst to attract leading experts from all over the world to this special place. Scientists conduct research that can improve our understanding of the ocean and the creatures that live there, and marine organisms’ response to an ever-changing environment.

Very few places exist in the South Atlantic waters of the United States that provide scientists the opportunity to compare habitats that are relatively absent of human influence against areas that are used by humans for recreation or other purposes. These and other research projects also bring economic benefit to our communities and can bring untold benefits globally, as scientists learn more about the ocean.

Although changes in the environment can take years to understand, it is this kind of steady progress that enables scientists to learn more and more about the ocean. The findings of these studies, coupled with relevant studies in other locations and our monitoring data, help us assess the overall condition of the sanctuary and ensure we are doing all we can do to protect the sanctuary’s marine life and ecosystems for future generations.

Michelle Riley is the communications and public outreach coordinator for Gray’s Reef National Marine Sanctuary