Why Are Scientists Exploring Chemosynthetic Communities in the Gulf of Mexico?
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.
On August 28, 2005, Hurricane Katrina swept across the Gulf of Mexico, gathering strength to become a Category 3 storm that proved to be the most costly - and one of the most deadly - hurricanes in U.S. history. Four days later, the Department of the Interior’s Minerals Management Service (MMS) reported that oil production in the Gulf of Mexico had been reduced by over 90 percent, and that natural gas production had been reduced by more than 78 percent. In the weeks that followed, fuel shortages and soaring prices underscored the importance of the Gulf of Mexico to petroleum supplies in the United States.
In fact, the Gulf of Mexico produces more petroleum than any other region in the Nation, even though its proven reserves are less than those in Alaska and Texas. The San Francisco Chronicle reports that oil companies are spending billions to find more crude oil and drill more wells. Even with the threat of more hurricanes, the Gulf of Mexico has advantages: oil workers are not in danger of being kidnapped by armed insurgents as is the case in Nigeria; no foreign president threatens to raise oil companies' taxes, as has happened in Venezuela; and OPEC doesn't control oil production in the Gulf of Mexico. As of August 1, 2005, a total of 41,188 wells had been drilled in the Gulf, and 1,259 petroleum fields had been discovered.
Much of this new exploration is focused on some of the deepest regions of the Gulf, made possible by improved technology and increasing crude oil prices (which have doubled in the last three years). In addition to new petroleum fields, this exploration has led to other discoveries as well. Some of the same conditions responsible for petroleum deposits also provide the basis for biological communities that receive energy from chemicals through a process called chemosynthesis (in contrast to photosynthesis that provides energy to terrestrial and shallow-water communities through processes in which sunlight is the basic energy source).
The first chemosynthetic communities were discovered in 1977 near the Galapagos Islands in the vicinity of underwater volcanic hot springs called hydrothermal vents, which usually occur along ridges separating the earth’s tectonic plates. Hydrogen sulfide is abundant in the water erupting from hydrothermal vents, and is used by chemosynthetic bacteria that are the base of the vent community food chain. These bacteria obtain energy by oxidizing hydrogen sulfide to sulfur: CO2 + 4H2S + O2 > CH2O + 4S +3H2O (carbon dioxide plus sulfur dioxide plus oxygen yields organic matter, sulfur, and water).
Visit http://www.pmel.noaa.gov/vents/home.html for more information and activities on hydrothermal vent communities.
Chemosynthetic communities in the Gulf of Mexico were found by accident in 1984. These communities are similar in that they are based upon energy produced by chemosynthesis; but while energy for the Galapagos communities is derived from underwater hot springs, deep sea chemosynthetic communities in the Gulf of Mexico are found in areas where hydrocarbon gases (often methane and hydrogen sulfide) and oil seep out of sediments. These areas, known as cold seeps, are commonly found along continental margins, and (like hydrothermal vents) are home to many species of organisms that have not been found anywhere else on Earth. Typical features of communities that have been studied so far include mounds of frozen crystals of methane and water called methane hydrate ice, that are home to polychaete worms. Brine pools, containing water four times saltier than normal seawater, have also been found. Researchers often find dead fish floating in the brine pool, apparently killed by the high salinity.
Where hydrogen sulfide is present, large tubeworms (phylum Pogonophora) known as vestimentiferans are often found, sometimes growing in clusters of millions of individuals. These unusual animals do not have a mouth, stomach, or gut. Instead, they have a large organ called a trophosome that contains chemosynthetic bacteria. Vestimentiferans have tentacles that extend into the water. The tentacles are bright red due to the presence of hemoglobin which can absorb hydrogen sulfide and oxygen which are transported to the bacteria in the trophosome. The bacteria produce organic molecules that provide nutrition to the tube worm. A similar symbiotic relationship is found in clams and mussels that have chemosynthetic bacteria living in their gills. Bacteria are also found living independently from other organisms in large bacterial mats. A variety of other organisms are also found in cold seep communities, and probably use tubeworms, mussels, and bacterial mats as sources of food. These include snails, eels, sea stars, crabs, lobsters, isopods, sea cucumbers, and fishes. Specific relationships among these organisms have not been well-studied.
Deepwater chemosynthetic communities are fundamentally different from other biological systems, and there are many unanswered questions about the individual species and interactions between species found in these communities. These species include some of the most primitive living organisms (Archaea) that some scientists believe may have been the first life forms on Earth. Many species are new to science, and may prove to be important sources of unique drugs for the treatment of human diseases. Because their potential importance is not yet known, it is critical to protect these systems from adverse impacts caused by human activities.
Ironically, one of the most likely sources of such impacts is the same activity that led to the discovery of these systems in the first place: exploration and development of petroleum resources. MMS has the dual responsibility of managing these resources as well as protecting the environment from adverse impacts that might result from development activities. In 1988, MMS issued regulations specifically targeted toward protecting deepwater chemosynthetic communities. An essential part of the protection strategy requires identification of seafloor areas that could support chemosynthetic communities. These areas must be avoided by drilling, anchoring, pipeline installation, and other activities that involve disturbing the seafloor. Describing deepwater biological communities and evaluating their sensitivity to impacts from human activities are key objectives of the Gulf of Mexico 2006 Expedition.
The objectives of the Gulf of Mexico 2006 Expedition are focused around three types of questions. First, what are the characteristics of biological communities - especially chemosynthetic communities - found on hard bottoms at depths below 1,000 meters in the central and western Gulf of Mexico? This group of questions includes:
- Similarities and differences between these communities and deepwater communities in the Atlantic Ocean as well as in shallower regions of the Gulf of Mexico;
- The relative abundance of larger mobile species in these communities compared to adjacent waters;
- Species, growth rates, and successional patterns of tubeworms in these communities compared to those in shallower waters;
- Feeding relationships in these communities compared to those in shallower waters; and
- Species composition and chemosynthetic activities of bacteria in these communities.
The second group of questions focuses on developing methods that use remote sensing information to predict the probable presence of sensitive biological communities at depths below 1,000 meters. Exploration for new petroleum fields usually involves collecting various types of chemical and physical data that provide clues about sea bottom characteristics, underlying geological formations, and the presence of hydrocarbon seeps. Since not all seeps and not all hard bottoms are associated with biological communities, key questions concern the specific physical and chemical features that correlate with the presence of these communities.
The third group of questions concerns the relative sensitivity of hard bottom and chemosynthetic communities to impacts resulting from human activity. Questions in this group involve the occurrence of rare species, unusual combinations of species, and the relative species diversity among sites. These characteristics can provide indications of communities that are particularly vulnerable to disturbance. If a species is confined to only a few sites, for example, this suggests that the species may have very specific requirements that are only met in a few areas. Such a species would probably be more vulnerable to environmental changes than another species that was found at many different sites.
The key piece of equipment for the Gulf of Mexico 2006 Expedition is the DSRV Alvin and its support ship, R/V Atlantis. Alvin, the first deep-sea submersible capable of carrying passengers, can dive to a maximum depth of 14,764 ft. A typical dive to a depth of about 6560 ft lasts about six hours. Film and video cameras are mounted on the outside of the submersible, and portholes allow direct observation forward and to each side with the assistance of Incandescent, sodium-scandium and thallium iodide external viewing lights. Two hydraulic manipulator arms mounted on the forward end of the submersible are used along with sediment corers and water samplers to collect samples. Electrode sensors will be used to take chemical readings of the environment, including concentrations of methane and oxygen. Other instruments include a computer/data display/recording system, an altimeter, a gyrocompass, a navigation and tracking system, sonar, an underwater telephone to communicate with Atlantis, and a magnetometer. Alvin also can be fitted with a variety of other specialized equipment to meet specific needs.
For more information about Alvin and Atlantis, visit http://oceanexplorer.noaa.gov/technology/subs/alvin/alvin.html.
Because many of the Expeditions questions involve identification of organisms, it is essential to be able to collect a variety of biological samples. The "Bushmaster" is an original instruments created by the research team of Charles Fisher (one of the senior Expedition scientists) to collect communities on and around hydrothermal vents. The instrument consists of a large collection net that can be closed from a submersible using a system of hydraulic cylinders and cables. The net collects intact communities of tube worms and almost everything associated organism larger than about 64 micrometers (0.0026 inches).
For more information about the Bushmaster, visit http://oceanexplorer.noaa.gov/technology/tools/bushmaster/bushmaster.html.
Another custom-built biological sampler, the ‘mussel pot’ is used to collect quantitative samples of bivalve mollusks (see http://oceanexplorer.noaa.gov/explorations/deepeast01/logs/sep22/sep22.html for more about mussel pots). In addition to these collections, biological communities and individual species will also be documented photographically. Mosaics made from multiple images can be used to produce detailed community maps that can provide a ‘baseline’ reference for detecting changes in these communities over time. Time lapse camera systems that can record the activities of mobile species will also be used.
As is the case with most scientific expeditions, a great deal of work will take place after the expedition itself is finished. Laboratory studies will include measurements of carbon, nitrogen, and sulfur isotopes to learn more about chemosynthetic processes and food webs; DNA analyses of biological specimens to help recognize species and taxonomic relationships; and microscopic studies to investigate growth rates in deepwater corals.