Why Are Scientists Exploring Davidson Seamount?
A key purpose of NOAA’s Ocean Exploration Initiative is to investigate the more than 95 percent of Earth’s underwater world that until now has remained virtually unknown and unseen. Such exploration may reveal clues to the origin of life on earth, cures for human diseases, answers on how to achieve sustainable use of resources, links to our maritime history, and information to protect endangered species. There is increasing evidence that seamounts and deep-sea corals are important fish habitat, hold data on ocean climate and productivity, and are hotspots of bio- diversity, including new species. Previous Ocean Exploration expeditions have documented deep- sea coral and seamount ecosystems in the Gulf of Mexico and off the coasts of New England, California, and the Pacific Northwest, but these missions have only begun to quantify these systems. These expeditions have yielded many new records of biota, new ecological data, new data on habitat distributions/structures, and data on water column trophic connectivity. The Exploring Ancient Coral Gardens Expedition continues and expands our explorations of these unique and relatively unknown deep water ecosystems, focusing specifically on the deep-sea coral species that are believed to play a central role in the ecological functioning of these systems.
Seamounts are undersea mountains formed by volcanic processes, either as isolated peaks or as chains that may be thousands of miles long with heights of 3,000 m (10,000 ft) or more. Compared to the surrounding ocean waters, seamounts have high biological productivity, and provide habitats for many species of plant, animal, and microbial organisms. Some of these species are important to commercial fisheries, while others are potential sources of new drugs to treat cancer and other diseases, as well as natural pesticides and nutritional substances. Deep- water corals are an important part of many seamount ecosystems, and the species diversity of these ecosystems is often comparable to that of corals reefs in shallow waters. Recent discov- eries suggesting that some corals may be hundreds of years old means that these organisms can provide important records of past climactic conditions in the deep ocean. Because many seamount species are endemic (that is, they are found nowhere else), the potential benefits of these species can only be revealed by specifically exploring these systems. In addition to potential benefits, deep-sea corals and seamounts are part of our world heritage; the environment we hand down from one generation to the next.
In recent years, it has become clear that the impact of human activities makes it even more important to explore seamounts and deep-sea coral ecosystems. Scientists at the First International Symposium on Deep Sea Corals (August, 2000), warned that more than half of the world’s deep-sea coral reefs have already been destroyed by commercial fishing, oil and mineral exploration, ocean dumping, and unregulated collecting. Protecting these unique systems and their potential benefits requires information about their biological and ecological relationships that can only be obtained through first-hand exploration.
Seamounts are the remains of underwater volcanoes that may be formed as isolated peaks or as chains that may be thousands of miles long with heights of 3,000 m (10,000 ft) or more. The volcanic processes that produce seamounts are often associated with the movement of the tectonic plates that make up the Earth’s crust. At spreading centers where these plates move apart (for example, along the mid-ocean ridge in the middle of the Atlantic Ocean) a rift is formed, which allows magma (molten rock) to escape from deep within the Earth and harden into solid rock known as basalt. Where tectonic plates come together, one plate may descend beneath the other in a process called subduction, which generates high temperatures and pressures that can lead to explosive volcanic eruptions (such as the Mount St. Helens eruption which resulted from subduction of the Juan de Fuca tectonic plate beneath the North American tectonic plate). Volcanoes can also be formed at hotspots, which are sort of natural pipelines to reservoirs of magma in the upper portion of the Earth’s mantle. Hotspots appear to remain stationary, while the tectonic plates gradually move across the hotspot location.
The Exploring Ancient Coral Gardens Expedition takes place on the Davidson Seamount, located about 75 miles southwest of Monterey, CA. This was the first geological feature to be described as a “seamount” in 1933. The now-extinct volcanoes that formed this and other nearby seamounts were different from typical ocean volcanoes. While the typical undersea volcano is steep-sided, with a flat top and a crater, seamounts in the Davidson vicinity are formed of parallel ridges topped by a series of knobs. These observations suggest that the ridges were formed by many small eruptions that occurred 3 to 5 million years apart. Typical undersea volcanoes are formed by more violent eruptions that gush out lava more frequently over several hundred thousand years.
Like corals found in shallow waters, deep-sea corals are members of the phylum Cnidaria, which also includes hydroids, jellyfishes, and sea anemones. One of the most conspicuous differences between shallow- and deep-water corals is that most shallow-water species have symbiotic algae (zooxanthellae) living inside the coral tissue, and these algae play an important part in reef- building and biological productivity. Deep-water corals do not contain symbiotic algae (so these corals are termed “azooxanthellate”), and receive nutrition from plankton and particulate material captured by their polyps from the surrounding water. Mounds of deep-water corals can alter the flow of currents and provide habitats for a variety of filter feeders. Technically, deep-water corals are ahermatypic (non-reef-building), but branches of some deep-water coral species (e.g., Lophelia pertusa) grow on mounds of dead coral branches that can be several meters deep and hundreds of meters long. Recent studies suggest that deep-water coral ecosystems may have a diversity of species comparable to that of coral reefs in shallow waters, and have found deep- water coral species on continental margins worldwide. There are just as many species of deep- water corals (slightly more, in fact) as there are species of shallow-water corals.
While deep-water corals are capable of building substantial structures, they are also quite fragile, and there is increasing concern that these communities and their associated resources may be in serious danger. Commercial fisheries, particularly fisheries that use trawling gear, cause severe damage to seamount habitats. Ironically, some scientists believe that destruction of deep-sea corals by bottom trawlers is responsible for the decline of major fisheries such as cod. Deep-sea coral communities can also be damaged by oil and mineral exploration, ocean dumping, and unregulated collecting. Other impacts may result from efforts to mitigate increasing levels of atmospheric carbon dioxide. One proposed mitigation is to sequester large quantities of the gas in the deep ocean, either by injecting liquid carbon dioxide into deep ocean areas where it would form a stable layer on the sea floor or by dropping torpedo-shaped blocks of solid carbon dioxide through the water column to eventually penetrate deep into benthic sediments. While the actual impacts are not known, some scientists speculate that since coral skeletons are made of calcium carbonate, their growth would probably decrease if more carbon dioxide were dissolved in the ocean.
The Exploring Ancient Coral Gardens Expedition is focussed on some of the most basic ques- tions about deep-sea corals, starting with “What’s your name?” The taxonomy of these corals, as indicated by their genetic composition, is a primary focus of the Expedition. Genetic information will also provide a better picture of the genetic diversity among coral species at the Davidson Seamount, as well as an indication of the extent to which these species are endemic.
Questions about the ecology of deep-sea corals focus on better understanding the factors that determine where these corals are found on seamounts. Based on previous expeditions, scien- tists have developed a simple model to predict where corals are most likely to be found and will test this model by visiting unexplored ridges, valleys, and slopes on the Davidson Seamount. Substrate, currents, and food availability are believed to be among the key factors that affect coral distribution.
A third set of questions concerns the age of deep-sea corals. Earlier expeditions found that some corals were several hundred years old. The 2006 expedition aims to refine estimates of age and growth rate using radioactive dating techniques. These studies will also examine how age and growth rate vary within and between coral colonies and locations on the seamount.
Seamounts and deep-sea coral ecosystems have not been widely studied because until recently they have been inaccessible to ocean explorers. Exploration is now possible through the use of deep-diving technology that will allow scientists to visually observe these ecosystems, as well as to collect specimens for laboratory studies. A key piece of equipment for the Exploring Ancient Coral Gardens Expedition is the Monterey Bay Aquarium Research Institution’s remotely operated vehicle (ROV) Tiburon. ROV Tiburon is a high-tech undersea robot connected to the surface by a long tether which carries electrical power, computer instructions, data, and high-resolution video. This ROV also carries a manipulator arm, suction sampler, push cores, Niskin bottles, and several instruments to measure currents. Visit http://www.mbari.org/dmo/vessels_vehicles/ tiburon/tiburon.html for more information about ROV Tiburon and its equipment. Laboratory studies of coral growth and age will measure the concentration of a lead isotope in different regions of the coral skeleton, and relate these concentrations to the known half-life of the isotope to obtain an estimate of the age of each region. Molecular biology techniques for DNA analysis will be used to study the genetic similarities of corals collected on the seamount, and to classify these corals into appropriate taxonomic groups.
For More Information
Contact Paula Keener-Chavis,
Director, Education Programs
NOAA Office of Ocean Exploration
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