Lisa Levin on the Ecology of Cold Seep Sediments
Fast Moving Front Commentary, November 2010
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Article: Ecology of cold seep sediments: Interactions of fauna with flow, chemistry and microbes
Authors: Levin, LA |
Lisa Levin talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Fronts paper in the field of Plant & Animal Science.
Why do you think your paper is highly
cited?
This paper brings together and synthesizes different types of biological research conducted on a relatively recently discovered deep-sea habitat, methane seeps. It also introduces elements of geology, biogeochemistry, and microbiology. Most of the attention in the 20 years between the discovery of methane seeps and the preparation of this paper had been on the large, visually charismatic animals at seeps (tubeworms, mussels, clams) or on the microbes.
I tried to gather information about the myriad of small organisms (cryptic protozoans and metazoans) occupying the sediment habitat. The sediment habitat is important because much of the microbial activity at seeps takes place in sediments; this distinguishes the seep ecosystem from its sister environment, the hydrothermal vents, which largely occur on hard substrates. Many authors studying deep-sea ecosystems cite this paper to document basic global trends in seep sediment communities.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
"Intense fishing activities, particularly trawling
threaten to severely damage seep environments before they are discovered.
This appears to have happened on the New Zealand margin and possibly the
Chile margin."
This is the first paper to review the different size groups of organisms occupying seep sediments. It discusses abundance and diversity trends, as well as nutrition in foraminifera, metazoan meiofauna, macrofauna, and megafauna, and looks for patterns across taxa among all seeps studied. This paper also links animal patterns to fluid flux and geochemical drivers. As with any newly discovered system, investigations at methane seeps have raised many new questions and I tried to highlight these in my synthesis.
Would you summarize the significance of your paper
in layman's terms?
This paper documents the strong link between geological processes, chemistry, microbiology, and animal communities that occurs at methane seeps. A hidden but complex ecosystem residing within deep-sea sediments is revealed. The review reflects the interdisciplinary nature of deep-sea biology and introduces the many tools (stable isotopes, geochemical profiles, evolutionary ecological concepts) that advance our understanding of reducing ecosystems in the deep sea.
How did you become involved in this research, and
how would you describe the particular challenges, setbacks, and
successes that you've encountered along the way?
My interest in methane seeps arose in the mid 1990s. I had been interested in the effects of environmental stress and organic inputs to sediment communities on the world’s continental margins. Methane seeps were first discovered in 1984. A decade later it had become clear that seeps were rather broadly distributed on continental slopes and presented unusual, highly sulfidic settings.
At that time most scientists were studying large seep animals. I thought it would be interesting to find out what smaller macrofauna lived in seep sediments, what factors controlled their distribution and whether they actually differed from "normal" slope faunas.
The greatest challenge to the study of methane seeps is their patchy, remote nature. I focus on settings well below scuba diving depths so an oceanographic vessel is required for study. Because seep activity is localized and seep patches are small (often 10-100 m2), a deep submergence vehicle such as a manned submarine or remotely operated vehicle (ROV) is required for sampling. Furthermore I conduct ecological experiments in situ, so I need to revisit the identical spot multiple times.
All of this is expensive, requiring large grants and access to vehicles that are much in demand. Initially the NOAA Undersea Research Program funded my work. Eventually the US National Science Foundation recognized the significance of methane seep science.
"This paper brings together and synthesizes different types of biological research conducted on a relatively recently discovered deep-sea habitat, methane seeps..."
Over the past 15 years I have been fortunate to have access to seeps in many parts of the Pacific Ocean. I often visit seep sites that have already been "discovered," but I look at them with new eyes and ask questions about types of organisms and habitats not yet examined. Each visit reveals new species, strange adaptations, and novel assemblages.
Where do you see your research leading in the
future?
I have become increasingly fascinated with the interactions of animals and microbes. Methane seeps are one place where archaea can be prevalent, thus offering the opportunity to ask questions about archaeal roles in animal nutrition, in substrate creation, and in habitat modification. The reverse questions are also interesting—i.e., how do animal activities affect microbes and geochemical environments?
Just as sediments once were a neglected seep habitat in the animal realm, I now believe that carbonate rocks—which are precipitated by microbes through anaerobic methane oxidation—potentially offer up a wealth of exciting seep animal biology. Further afield, I would like to explore the relationship between seep ecosystems and other reducing environments (vents, organic falls, oxygen minimum zones), and examine the ecology of animal communities reside in the deepest half of the ocean, our trenches.
Do you foresee any social or political
implications for your research?
Methane seep environments are not well known and most have probably yet to be discovered. But they are susceptible to human influence on many fronts. Increasingly deeper fishing activity has targeted taxa that like to "hang around" seep hardgrounds (e.g., Chilean sea bass, sablefish, rockfish). Intense fishing activities, particularly trawling, threaten to severely damage seep environments before they are discovered. This appears to have happened on the New Zealand margin and possibly the Chile margin.
Seep communities are often associated with methane hydrate deposits (methane trapped in water crystals) and also petroleum deposits. As such they are linked to a massive hydrocarbon reservoir that remains a possible energy source for humans, but is also susceptible to damage by exploitation, or to methane release by global warming. Any methane released into the atmosphere could exacerbate the warming climate. Mining of gas hydrates as an energy source remains a future possibility, with potential effects on the ecology of seep ecosystems.
Dr. Lisa A. Levin
Professor of Biological Oceanography
Integrative Oceanography Division
Scripps Institution of Oceanography
University of California, San Diego
La Jolla, California, USA
KEYWORDS: GULF-OF-MEXICO; SANTA-BARBARA BASIN; ANAEROBIC METHANE OXIDATION; STABLE ISOTOPIC COMPOSITION; CASCADIA CONVERGENT MARGIN; EASTERN MEDITERRANEAN SEA; ALEUTIAN SUBDUCTION ZONE; PORE-WATER CHEMISTRY; MID-ATLANTIC RIDGE; FLUID-FLOW.