Scientists Cruise Deep into Coral Ecosystems
Research cruises exploring the seafloor of the Atlantic Ocean and Gulf of Mexico are opening up a new world of organisms and ecosystems to scientists as researchers descend into uncharted territory hundreds of meters below the sea surface. Several U.S. Geological Survey (USGS) scientists are co-leading a team of researchers from around the United States and Europe seeking to characterize deep-coral ecosystems and the abundance of organisms that live in and around them. Their research is shining a light on some of the darkest and least explored places on the planet.
In direct contrast to the shallow, colorful coral reefs full of tropical fish found in such places as the Great Barrier Reef and the Florida Keys are the equally colorful corals that thrive in dark, extremely cold undersea places being explored by scientists in the DISCOVRE program (Diversity, Systematics, and Connectivity of Vulnerable Reef Ecosystems). The purpose of the program is to uncover and document what exists at depth and begin the process of protecting deep-coral ecosystems. This interdisciplinary, global research initiative has already had positive impacts on deep-sea conservation. On the basis of current research, the South Atlantic Fishery Management Council has approved an amendment to protect more than 23,000 mi2 of deep-coral habitats, ranging in depth from 370 to 800 m, off the coasts of the Carolinas, Georgia, and eastern Florida.
The 4-year multidisciplinary DISCOVRE research program includes expeditions that are a partnership among the USGS; the Minerals Management Service (MMS); the University of North Carolina, Wilmington; the University of North Carolina at Chapel Hill; the National Oceanic and Atmospheric Administration (NOAA); the Royal Netherlands Institute for Sea Research; and the Scottish Association for Marine Science. The expeditions focus on understanding the physical oceanography, biology, ecology, and genetic connectivity of deep-coral environments.
This year, the DISCOVRE team was involved in three cruises in the Atlantic Ocean and Gulf of Mexico. Their first cruise, in early August, explored deep-coral ecosystems off Cape Canaveral, Florida. Two USGS scientists, Amanda Demopoulos and Cheryl Morrison, went straight from that cruise to participate in a NOAA Ocean Explorations cruise funded jointly by NOAA and MMS, and then directly from that to another DISCOVRE cruise. Both the second and third cruises explored the Gulf of Mexico from offshore of Texas to the west Florida slope.
"We have for decades known that deep-sea corals exist in U.S. waters, based on a few biological and geological studies done in the Gulf of Mexico and off the southeastern United States. However, intensive deep-coral research in the area only began within the last decade," said Amanda Demopoulos, a benthic ecologist with the USGS in Florida and co-principal investigator for the DISCOVRE program. Demopoulos is characterizing the diversity and abundance of small animals living within the coral matrix and nearby sediments.
"Our goal is to understand the diversity and ecology of deep-sea coral environments across these biogeographic regions, compare our data from the Gulf and southeastern U.S. with ongoing research in Europe, and communicate the combined results to scientific and governmental organizations," she said.
DISCOVRE expeditions use a combination of techniques—including photography, sample collection, multibeam sonar, and submersible dives—to examine deep corals and identify organisms ranging from microbes to fish. Submersibles descend hundreds to a thousand meters below the sea surface and enable their occupants to videotape the environment and collect specimens, as well as take measurements of temperature, salinity, dissolved oxygen, and currents.
Two benthic landers—stable sea-bottom platforms that suspend sensors, cameras, and data-acquiring gear—were deployed during annual cruises to document the deep-coral environments and associated biological activity, providing a long-term window into these ecosystems. In addition, a newly developed lander, a microlander, was designed to record the deep-sea environment without the lights and noise of a submersible. Altogether, these sampling and digital-recording techniques leave little or no permanent footprint on the environment while yielding tremendously valuable information.
To collect samples near deep corals, Demopoulos uses push cores, clear plastic tubes with a T-handle, held in the exterior arm of the submersible and pushed into the sediment vertically. A rubber gasket at the base of the T-handle creates a vacuum that keeps the sediment sample within the core as the sub pulls up on the T-handle to retrieve the core. The core is then placed in a cylindrical container called a "quiver" and brought back to the ship for researchers to analyze the organisms in the sediments.
"I have collected more than 600 samples from this summer's cruises, and we are beginning to find organisms in the sediments that we haven't yet seen in the lab," said Demopoulos, who was in charge of sediment collections of coral-associated meiofauna (animals between 0.045 and 0.29 mm in size) and macrofauna (animals more than 0.30 mm) from all three cruises. Analysis of the core samples may lead to the discovery of new species. Because cores were taken both near corals and farther away, they will shed light on whether the presence of corals enhances the diversity of the marine benthos.
In addition to gathering and studying organisms living around deep-coral ecosystems, researchers are extracting microbial DNA directly from the corals for analysis. "Multiple studies have shown that shallow and deep corals host complex and diverse bacterial communities that are distinct from those in the water column," said Christina Kellogg, a research microbiologist with the USGS in Florida.
Kellogg collects mucus, tissue, and skeletal matter from corals in deep water using a sealing bin that she and her husband designed. The bin contains 10 individual chambers that keep samples from touching each other or being exposed to the water column. DNA is extracted from the samples and then sequenced to provide estimates of bacterial diversity. Understanding microbial diversity can provide greater insight into the overall coral ecosystem.
"The presence of coral-species-specific bacteria makes it clear that these interactions are not random or passive. Coral-associated bacterial populations are closely attuned to host metabolism and may change in number or composition in response to a change in coral health, making the bacterial populations a possible diagnostic of coral health. Bacteria may also ward off other potentially harmful microbes by producing antibiotics or just by occupying the available space," said Kellogg.
In December, DISCOVRE will explore deep corals off the coast of North Carolina, and benthic landers will be deployed to make observations for a year. The project will continue through 2011 to characterize and discover more deep corals on the seafloor.
For additional information, visit the DISCOVRE Web site or read a USGS Fact Sheet describing the project: Gulf of Mexico Deep-Sea Coral Ecosystem Studies, 2008-2011. Also see "Flat Isabel Goes on a Research Cruise," in the Outreach section of this issue.
in this issue:
Scientists Cruise Deep into Coral Ecosystems