Photo by Gregory S. Boland

A Big Discovery in the Gulf of Mexico!

It is not widely known that the Gulf of Mexico is home to some remarkable deep-sea animals that are usually associated with geological features in the major ocean basins. These animals literally eat dissolved gasses! In 1984, two teams of scientists independently discovered these "chemosynthetic" life forms on the floor of the Gulf of Mexico thousands of feet below the water surface. These exciting discoveries (one made by Texas A&M University, the other by LGL Ecological Research Inc., then under contract to the Minerals Management Service and the oil and gas industry) were quite unexpected. As we will see, these animal communities and the species that comprise them are remarkable in many ways.

Background

The landmark National Environmental Policy Act (NEPA) of 1969 and several other laws have made it incumbent on Federal agencies to accumulate environmental information to support their management decisions. Since 1973 the Minerals Management Service has supported many coastal and marine environmental studies to obtain scientific information for its management of the offshore oil and gas industry.

Most of the scientific investigations of the Gulf of Mexico have been done on the Gulf's continental shelf, the shallow underwater platform adjacent to the shoreline and extending out to a depth of about 200 m (~660 feet). These studies, which continue in earnest, have been spurred on by the continuing development of the offshore oil and gas industry. Today, the continental shelf in the western and central Gulf of Mexico is distinctive in its population of thousands of fairly shallow offshore platforms, some of which have been in place for decades.

Minerals Management Service Studies of the Deep-Sea in the Gulf of Mexico

Detailed and credible environmental information on the deep Gulf is needed because the oil and gas industry has accelerated its search for producible oil and gas reservoirs beyond the shelf onto the continental slope. The industry expects new exploration and production in depths out to 3,000 m in the near future.

Only a few years ago technical and engineering considerations limited the depths in which oil and gas operators could explore for oil and gas, then produce it if they found it. Now, thanks to recent technological advances, the limiting factors are chiefly the costs involved. So, given the right market prices and a petroleum reservoir of sufficient size, the investment is economically justifiable. The Minerals Management Service has stimulated this trend with royalty relief in deep water

The MMS has supported over a dozen deep-sea-related efforts including scientific workshops, deep-sea information reviews, and six multi-million-dollar shipboard investigations. The first comprehensive field study of the deep sea in the Gulf of Mexico (the "Northern Gulf of Mexico Continental Slope Study") was commissioned by MMS in 1983. This study concentrated on the geologic features, water masses, chemistry, and biological communities of the northern Gulf from depths of 300 meters down to the abyss. These greater depths, in the area known as the continental slope (as opposed to the shelf), extend from water depths of about 200 meters, at the "shelf-slope break", into thousands of meters of water. (A meter is equal to 3.28 ft.) Relatively little was then known about this deep-water area, compared with the shallower continental shelf. We are learning more about it with every passing year. The second general study, known as the Northern Gulf of Mexico Continental Slope Habitats and Benthic Ecology Study was begun in 2000.

The discovery of the first Central Gulf chemosynthetic communities was made during the "Northern Gulf of Mexico Continental Slope Study". (The first discovery in all the Gulf was made on the Florida escarpment by the Alvin submersible just a few months earlier in March, 1984.)  This remarkable ecosystem became the subject of two additional major field studies known as "Chemosynthetic Ecosystem Study" and "Stability and Change in Gulf of Mexico Chemosynthetic Communities."

Life in the Deep-Sea

Colorful crab perched on top of a large tubeworm cluster at GC 354, depth 532 m. This community was first discovered on this MMS/LSU subdive, August 24, 2000.

In most respects, the deep-sea biology of the GOM is similar to that in other subtropical and temperate basins. For the most part, benthic (bottom-dwelling) deep-sea animals live under conditions of perpetual darkness and low temperature. Typically, the bottom consists of nearly featureless silt, ooze, and mud. Here, there are very sparse food resources. Devoid of living plant material, the ultimate source of food for life is the energy-poor remains of organic materials that rain slowly from above. Most deep-sea animals tend to be generally small and fragile and they display low densities and overall biomass. All have developed anatomical characteristics, and physiological and biochemical adaptations to cope with these conditions.

In contrast to the deepsea, surface waters, especially those closer to shore, tend to be rich in life; it is near the surface and in the presence of sufficient sunlight, that small drifting plants called phytoplankton, and larger algae and seagrasses (with their green pigment, chlorophyll), convert dissolved carbon dioxide gas and water into simple sugar through the chemical process called photosynthesis:

Photosynthesis is a process resulting in biochemical food production that ultimately drives and supports the ecosystem, up to and including the largest predators at the top of the food chain, such as seals, sharks and killer whales. It is called primary productivity because it is at the very bottom of the food chain. Animals that eat other animals or plants are termed consumers. Photosynthesis also recharges much of the world's oxygen supply. This singular process, the one supporting the whole biosphere of the planet, has been recognized for centuries.

In 1977 a second type of primary productivity was discovered. It was then that other remarkable forms of life, chemosynthetic animals, were unexpectedly discovered on dives of the deep submergence vehicle (DSV) Alvin in the Pacific Ocean. This discovery shook the foundations of marine biology. It was called by some, the most important biological discovery of the 20th century. Photosynthetic production was replaced by chemosynthesis. Some of the animals didn't even have a mouth or gut! And in 1984 it was found that these same kind of animals were living in the Gulf of Mexico too.

Chemosynthetic animals were found to be able to extract their energetic needs from dissolved gasses in their environment in the presence of dissolved oxygen. These first chemosynthetic animals, huge tube worms (known as vestimentiferans) and clams, were discovered living near hydrothermal (hot-water) vents in the spreading seafloor at the mid-ocean ridge. These remarkable animals were obtaining their energy from dissolved hydrogen sulfide issuing from the vents. To accomplish this the animals held certain bacteria within their tissues in a mutually-beneficial ("symbiotic") relationship. Today, similar chemosynthetic animal communities have been discovered in many locally-unusual habitats all around the world where the necessary gasses vent or seep from the ocean floor. In the Gulf there are "cold seeps" at the bottom that variously release hydrocarbons (mostly methane) or hydrogen sulfide depending on the local geology. But the chemistry of both seeps and vents would be considered inhospitably toxic for many "conventional" forms of life.

In addition to the animals' novel biochemistry, the chemosynthetic animals are quite large, as deep-sea animals go. Also the communities are very densely populated. The very high density and biomass of these large chemosynthetic forms were the "exception that proved the rule" that the main limiting factor to the deep-sea fauna is the availability of nutrients. Here the nutrients (gasses) are abundant, and in many cases flow freely out of the bottom.

 

Photo by Gregory S. Boland for LGL/MMS

Well-developed Gulf chemosynthetic communities were first discovered near natural hydrocarbon seeps in the north central Gulf of Mexico.  The image to the right was the first taken insitu by a deep-towed camera system at a depth of 635 m in block GC 81, November 12, 1984, during the MMS Northern Gulf of Mexico Continental Slope Survey.  The first community observed first-hand by scientists in a submersible was a prominence later named "Bush Hill" for its "bushes" of tube worms. Through Minerals Management Service support of additional studies, these Gulf communities were shown to be similar in many ways (and different in others) to other discoveries around the world. In all cases, chemosynthetic forms were shown to harbor huge numbers of bacteria in their bodies and to possess various anatomical and physiological adaptations and intricate biochemical pathways, that allowed the use of chemical compounds by the bacteria and protected the animals from toxicity. In all cases they are orders of magnitude greater in biomass than the surrounding fauna. The known Gulf communities live in water as shallow as 400m. This puts them within reach of modest-depth submersibles such as the Johnson-Sea-Link I and II, making them accessible laboratories for sampling and experimentation. The same geological features that make the Gulf of Mexico an important petroleum province are the same reasons that seeps and chemosynthetic communities exists. This clearly presents a management conflict.

Regulatory Actions

With the discovery of the Gulf chemosynthetic communities, the MMS recognized the special value of these communities. In cooperation with industry, the Minerals Management Service developed rules that required the oil and gas industry to protect them from the physical effects of continental slope exploration and production. In 1988, the MMS issued regulatory guidelines (a "Notice to Lessees" or NTL) which became effective in 1989. The guidelines were revised and updated in 2000 (now NTL 2000-G20). The guidelines require "....avoidance or protection of chemosynthetic communities and avoidance of shallow hazards...." It required that, in depths greater than 400 m, companies would provide data needed by the MMS to determine whether there was the potential for the local existence of chemosynthetic communities. Further, companies must delineate and identify all seafloor areas to be disturbed, as well as any evidence that the area might support chemosynthetic communities. If the MMS review suggests that chemosynthetic communities might be present, the company must either (1) modify their plan and relocate the operation, (2) modify the application to provide additional photographic or videotape information to determine the presence or absence of well developed communities, or (3) otherwise ensure that their activities do not impact a community (e.g., through the precise placement of anchors).

Information Needs:  The Field Studies

Beyond the regulatory actions, the MMS also recognized the need for a more comprehensive understanding of these communities in the Gulf. So, in 1991, the MMS funded the "Chemosynthetic Ecosystems Study," which was successfully conducted by the Geochemical and Environmental Research Group (GERG) of the Texas A&M University (TAMU). This effort provided important multidisciplinary data at a limited number of sites believed to be representative of upper-slope chemosynthetic communities. (The report, titled "Chemosynthetic Ecosystems Study: Final Report," was published in 1995 and is MMS Report 95-0021.) A follow-up study, "Stability and Change in Gulf of Mexico Chemosynthetic Communities" was awarded to the same group. That report will be available in 2001.

The objectives of the Chemosynthetic Ecosystems Study Program (1991-2001) were to:

• Gather and synthesize all available information on Gulf of Mexico chemosynthetic communities.

• Develop models which explained patterns of distribution and abundance of chemosynthetic communities.

• Identify, what types of animals comprise the communities, and to describe their relationships with other animals.

• Determine the factors (e.g., depth, temperature, water chemistry, sediment types, and dissolved gasses) which influence the distribution, abundance and growth of chemosynthetic communities. Determine the sources of dissolved gasses.

• Determine whether chemosynthetic communities are robust or fragile and whether they are essentially permanent or ephemeral

• Characterize the age, growth rate, turnover rates, reproduction and recruitment, and patterns of senescence and death in the dominant chemosynthetic animals; examine recovery rates of communities damaged by physical disturbance; and

• Determine the reliability of methods for detecting chemosynthetic communities using remote acoustic and/or geophysical devices, imaging instrumentation, hydrocarbon measurements, and/or other available technologies.

To address these difficult objectives, the research team developed an ambitious research plan. Because the distribution and abundance of the communities were believed to result from small-scale (only meters to tens of meters) changes in the presence of seeping gasses and geological features, conventional shipboard sampling methods (e.g., dredging, coring, trawling, and water collections) would be abysmally inadequate. Therefore, direct observations and samples were taken with the two Johnson-Sea-Link (JSL) research submersibles owned and operated by the Harbor Branch Oceanographic Institution (HBOI). The HBOI made the necessary modifications to the JSL's accommodate highly specialized pieces of scientific equipment and samplers. Innovative devices for the unique needs of individual scientists were also designed (e.g., a tube-worm banding device used for the estimation of worm growth over time.) The scientific team was composed of investigators from Texas A&M University, Pennsylvania State University, Woods Hole Oceanographic Institution, and the Dauphin Island (Alabama) Sea Laboratory. The researchers represented numerous areas in the biological, biochemical, chemical, radiochemical, geophysical, and geological sciences. They sampled sediments, rocks, mollusc shells, water, seeping oil and gas, bacterial mats, and animals of all sizes (chemosynthetic and otherwise). These samples were augmented by untold hours of videotape and 35mm film, and miles-worth of various geophysical and side-scan sonar records. These samples were subjected to a myriad of processes, preservations and dissections; chemical, isotopic, and biological analyses; and x-rays, counts, and measurements. The communities and habitats were mapped using sophisticated computers and software.

The MMS "Chemosynthetic Ecosystems Program" has revealed many intriguing facts about chemosynthetic communities and animals, and ways to conduct research. For example:

• All Gulf seep species studied to date have a very slow growth rate. Some of the larger tube-worms may be centuries old and are believed to be the oldest living animals on earth. This stands in stark contrast to the hydrothermal vents animals which recolonize and grow rapidly following cataclysmic events (for example, covering by molten lava).

• When disturbed; for example, buried and suffocated by natural events such as turbidity flows; the same type of community will eventually grow back, given the same local geochemical conditions. Community successions have been documented over 2,000 years, during which time there were several temporary extinctions.

• The removal of oil and gas from subsurface reservoirs during production is not predicted to deprive the communities of the necessary gasses for survival.

• Photo by Gregory S. Boland

  Unexpectedly, researchers have learned that while the chemosynthetic communities are locally productive habitats, only a little of the living carbon in the system supports the surrounding heterotrophic (non-chemosynthetic) food chain. But the communities do harbor myriads of heterotrophic animals, large and small, effectively mimicking a deep-sea "reef." The successional building of some of the communities involves the bacterial building of carbonate rock and gas hydrate "ices". Both offer unique ecological niches for fauna of many types. Non-chemosynthetic species, include fishes, crustaceans, echinoderms, and snails. A new species of segmented worm (Hesiocaeca methanicola, the "iceworm"), was found sculpting exposed gas hydrates.

  Photo by Charles Fisher/Penn State

• Communities can change rapidly over distances of only a few meters in response to the distribution of microhabitats. There are no "typical" communities even though only a few chemosynthetic species make up the vast majority of the biomass.

• The number of known chemosynthetic communities in the Gulf of Mexico now exceeds 40, ranging in depth from a few hundred meters to 3,000 m. Judging from the distributions of natural surface oil slicks seen from space, there are likely to be hundreds of seeps in the Gulf. Some surface slicks coincide well with known positions of chemosynthetic communities. How many seeps support chemosynthetic communities is anyone's guess. The levels of natural oil and gas seepage in the Gulf is great. In an area of about 15,000 square kilometers (i.e., a square only 66 nautical miles on a side) may be between 100,000 and 400,000 barrels per year. (A petroleum barrel is 42 gallons.)

• The types of data received during geophysical surveys may be used to allow researchers to make educated guesses about the locations of chemosynthetic communities. Certain features such as "wipe-out" zones can indicate the presence of gas and possibly chemosynthetic communities.

• Mussel communities can be short-lived. Studies have shown that accumulations of dead mussel shells can be no older than 15 - 20 years old. But photographs of some sites show little variation in living mussels and tube worms from year to year. More research would be needed to determine rates of change and levels of variation.

• Naturally-occurring anoxic brine pools have been discovered which can kill fish swimming within the pools. But the same pool fuel surrounding mussel beds only inches away with gas. Mussels which fall into or are submerged by the pool soon die because the pools are very low in oxygen and are far saltier than ambient water and some are much warmer.

• Several chemosynthetic community species have proven to be new to science. But they are closely related to other species found elsewhere (themselves discovered only in the last quarter century). Chemosynthetic community structures worldwide have major type species in common.

• The zoogeographic relationships and evolutionary histories have yet to be worked out, but larval dispersal are likely akin to those requiring "island hopping" to spread. Manned research submersibles have so far proven to be the only viable means to conduct the types of surveys and collections needed in deep specialized habitats. Recent independent experiments show that tiny tube worms will occupy areas charged with organics that release hydrogen sulfide. This is similar to the conditions resulting from whale deadfalls where tubeworms have been found too.

Report Availability and ESPIS

The report, MMS 95-0021, is titled "Chemosynthetic Ecosystems Study: Final Report."

Copies of the final report of these studies are/will be available through the MMS Gulf Public Information Office at the following address:

Minerals Management Service
Public Information Office
1201 Elmwood Park Boulevard
New Orleans, Louisiana 70123-2394
(504) 736-2519 or 1-800-200-GULF

The Environmental Studies Program Information System (ESPIS) is a free, computerized database established by MMS to make information gathered by the Environmental Studies Program more widely accessible. This System allows full text search and retrieval of this scientific information. Copies of many of the Environmental Studies Program reports and pertinent Technical Summaries are available by searching ESPIS.

Chemosynthetic Communities in the Gulf of Mexico Poster and Teacher's Companion: Description and Ordering Information