Laura Nielsen for Frontier Scientists
Deep sea oceans, once believed lifeless, teem with an astounding biodiversity. Where once we knew only speculation and fishermen’s tales, we now have a body of knowledge increasing with data from remotely operated underwater vehicles (ROVs) and human-occupied submersibles like James Cameron’s Vertical Torpedo. The deep ocean, the last unexplored terrestrial frontier, holds many surprises. Will those surprises survive human inputs?
Lisa Levin, Director of the Center for Marine Biodiversity and Conservation and Distinguished Professor at the Scripps Institution of Oceanography in California and veteran marine scientists, recognizes what she calls “The long arm of human need.” Resource exploitation and human-impacted climate change are having powerful effects on the organisms which live in ocean ecosystems. The list of threatened and endangered species continues to grow. And in the oceans- just as in the jungles- we are damaging and driving species extinct before we even discover and document their existence.
I attended Levin’s talk at the 2012 American Geophysical Union Fall meeting in San Francisco, where earth and space scientists convene yearly. Her recent work has centered around continental margins, deep-sea zones which lie off the edge of the continents. Levin is engaging, a good trait in a scientist who knows that people won’t protect the things they’ve never heard about, never imagined. She speaks of benthos- organisms that live at or near the seabed, often on or within the sediment that makes up the seafloor. These creatures are adapted to harsh sea regions where it is intensely cold, very salty, and the pressure is high. In hypoxic zones deep underwater, there is almost no dissolved oxygen. Still species are able to thrive. Many deep-sea critters use chemosynthesis, converting chemicals into food and energy (as opposed to photosynthesis, in which organisms take energy from the Sun) because very little light penetrates to the depths where they live. There are tubeworms which live in colonies, forming bushes the size of cars. Deep cold-water coral mounds stretch for kilometers on seamounts. Aleutian sponges act as rockfish nurseries.
“50 miles off the coast of Oregon, the mud on the bottom of the sea is more alive than dead. Thousands of feet below the surface, under pressures that would crush you and me, in temperatures that would turn our blood to sludge, worms, crustaceans, snails, bacterial filaments, and other life-forms as yet undescribed thrive in an environment largely devoid of oxygen and toxic with hydrogen sulfide and methane.”
Ecosystems get creative. Some are built entirely around the carcass of a single whale. Whale-falls can support Osedax, ‘bone-eating worms’ that feed on lipids inside the bones, for tens or hundreds of years after the whale’s bones come to rest on the sea floor. Elsewhere around hydrothermal vents (geothermally heated vents) or cold seeps (cold vents from which seep hydrocarbons like methane) communities flourish. Yeti Crabs have oversized front arms, where they host a personal garden of bacteria. Waving their arms in a cyclical motion, the Yeti Crabs cause methane to waft over the bacteria; the bacteria feed on the methane, and in turn the crabs feed on the bacteria. The microorganisms that engage methane through chemosynthesis are to be cherished… methane is more than 20 times more effective at trapping atmospheric heat than carbon dioxide, so the beings that consume it before it reaches the atmosphere do our world a great favor.
The creatures which have adapted to ocean environments, though, will almost certainly struggle to meet the fast-paced change enforced by anthropogenic (human-caused) climate change, not to mention direct man-made impacts on their environments.
Waters exposed to rising atmospheric carbon dioxide means the oceans face acidification, which threatens especially corals and shelled creatures like mollusks and crustaceans. More carbon entering ocean waters from the atmosphere and slowly churning lower means more acidity (a lower pH level) and less oxygen. Surface-area waters warm, and warmer water holds more oxygen, which withholds oxygen from the deep. With less oxygen inundating the depths, the deep hypoxic zones expand upward toward the surface. Fish and other sea creatures must accept the habitat compression imposed by the stratified ocean. If not, they must either enhance their oxygen uptake or accept high carbon levels in order to cope. However, not all can cope, and experience hypoxia (when the body is deprived of adequate oxygen) and hypercapnia (when there is too much carbon dioxide in the blood).
All those fish who are unable to tolerate the low oxygen levels of the expanding hypoxic zones and are pushed into a smaller feeding zone become easier prey for both natural predators and fishermen. Unregulated fishing leads to overfishing of populations. Meanwhile bycatch, fish that die during fishing even though their species was never targeted, and “ghost fishing”, when sea creatures become entangled in discarded fishing gear and die because of human trash, threaten species still further. Trawling scrapes at the seafloor, destroying undiscovered species and scarring the environment. Oil spills represent a tremendous risk to ecosystems. Oil drilling with unproven or ineffective cleanup plans for spills threaten destruction in many areas of the world, like the Bering Sea’s ecologically intriguing Pribilof Canyon which supports Bowhead Whales, myriad crustaceans, and other less loveable but still vital species. And deep-sea mining, a newer threat, combines with mine tailings from land which have been deposited carelessly into the deep sea to add toxic compounds to ocean waters.
Lisa Levin points out these dangers, asks ‘How can we maintain the integrity of our deep-sea ecosystems?’, and gives advice in her Sverdrup Lecture, which you can currently listen to here at the AGU2012 website: Deep Margins Under Pressure: Sustaining Biodiversity and Function where Climate Change and Humans Collide. She asks us to reexamine our priorities. We need to think conservation.
Find out much more about marine and terrestrial science at Frontier Scientists
Lisa Levin in Sverdrup Lecture: Deep Margins Under Pressure: Sustaining Biodiversity and Function where Climate Change and Humans Collide http://fallmeeting.agu.org/2012/events/sverdrup-lecture-os53f-deep-margins-under-pressure-sustaining-biodiversity-and-function-where-climate-change-and-humans-collide-video-on-demand/
Julia Whitty in Gone: Mass Extinction and the Hazards of Earth’s Vanishing Biodiversity http://www.motherjones.com/environment/2007/05/gone