Is Marianas Trench A Lifeless Void?

When he made his historic solo dive into the Mariana Trench last month, James Cameron brought back images and descriptions of a “lunar like” marine landscape nearly devoid of life.-via National Geographic

Returning from humankind’s first solo dive to the deepest spot in the ocean, filmmaker James Cameron said he saw no obvious signs of life that might inspire creatures in his next “Avatar” movie but was awestruck by the “complete isolation.” –via Christian Science Monitor

The quotes above illustrate just two of the many mainstream media pieces that highlighted James Cameron’s comment of a lifeless landscape at the bottom of the Marianas Trench.  However, Cameron fell into a trap nearly 200 years old.

Edward Forbes is the whipping boy of deep-sea biology.  Forbes’s big mistake was concluding, in the mid-1800s, that marine life could not exist deeper than 550 meters, what he called the “azoic hypothesis.” Given the state of knowledge at the time, it seemed logical that no species could survive under the extremes of high pressure, lack of light, and cold temperatures characterizing the deepest ocean. Unsurprisingly, Forbes’s thinking spread quickly among the scientific community. The azoic hypothesis ultimately proved wrong or this blog would have a lot less fodder for writing and a different title.  How Forbes was wrong is the interesting part.

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A satellite image displaying the amount of Chlorophyll a, an indicator of phytoplankton. In the eastern Mediterranean you can see predominantly dark blue colors indicating little Chlorophyll a.

Forbes based is azoic hypothesis on sampling he did in the eastern Mediterranean Sea, an area that sees little phytoplankton production.  With less food at the ocean’s surface, less food will sink to the deep ocean floor resulting in little abyssal life.  Unsurprisingly, when Forbes pulled his trawled samples from the deep they were not brimming with a cornucopia of life.

Forbes also didn’t know that the low food arriving to the deep sea miniaturized animals.  In one of the earliest papers on the deep-sea fauna, Mosely (1880) noted, “Some animals appear to be dwarfed by deep-sea conditions.” Almost a century later, Hessler (1974) noted that “individuals of certain taxa are routinely so small that they are of meiofaunal size.” Thiel (1975) echoes these comments by noting the deep sea is a “small organism habitat.”

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Busycon carica

Consider that the entire collection of deep-sea gastropods from the western North Atlantic collected under the WHOI’s Benthic Sampling Program (44 samples, 20,561 individuals) would fit completely inside a single Busycon carica, a typical-sized New England knobbed whelk.  Forbes nets with their big mesh size allowed most animals to pass right through.  Today of course we use finer mesh sizes on nets or cores so we don’t miss the diversity of small life.

I cannot help but wonder if Cameron fell into the same trap that Forbes did so long ago, an underappreciation of the complexity and uniqueness of deep-sea life.

Was he waiting for charismatic megafauna that never arrived and potentially never existed at the deepest point in the ocean?

Bob McDondald in a recent Op-Ed  stated,

… there is no substitute for good science. Big budgets and lots of publicity gather public attention – a stunt such as a solo dive to the deepest part of the ocean will get an explorer into the history books, just as a free fall from the edge of space did.  But these are often one-off events. The whole point of the exercise was to get there. Science, on the other hand, is a systematic, step-by-step process that explores carefully, building on past successes and putting new discoveries into the broader context of the scientific community. A robot sub being hauled out of the water may not look as dramatic as the scene of a hatch opening and the triumphant explorer emerging to a cheering crowd, but what the science actually reveals is the most dramatic of all

Of course, I would be remiss not to mention another point glossed over and even blatantly misrepresented in the media.  Cameron’s dive, while worthy of praise on many fronts, is a not the first exploration of the deepest part of the ocean.  Scientists, especially Japanese researchers, have been sampling the bottom of the trench extensively for a few decades with robots and landers.

As McDonald points out, and the labor of many expeditions and scientists has demonstrated, the Marianas Trench is actually full of life.  Although contrary to what McDonald claims new research didn’t reveal this fact but only supports what we’ve known for a while.

Marianas Trench is teeming with microbial life.  In 1997, a species of the common bacteria Pseudomonas was discovered from 11,000 meters deep. In 1998, Japanese researchers using the remotely operated vehicle Kaiko found evidence of two barophilic, pressure loving as you would expect from trench critters, bacteria.  Both bacteria species were from completely different groups.  In 2006, Japanese researchers hit a biological gold mine of microbes.  Actinobacteria, non-extermophilic bacteria, three major groups of extremophilic bacteria, fungi…O my! And o’ how the reports of new microbial species just keep coming, and coming, and coming, and coming, and coming, and coming in.  Indeed, microbial activity is shockingly high…even for those of us expecting it.

Forams from Marianas Trench

Forams from Marianas Trench

Naysayers will surely point out how bacteria somehow don’t count as real life.  They live everywhere. These people have some size threshold for life to count. I give you naysayers protists!  Foraminifera, amoeboid protists vital for nutrient cycling in the oceans, also exist at the greatest depths of the Marianas Trench.  Perhaps some will need something even larger…a metazoan.

H. gigas

Hirondellea gigas

Multicellular life is also known from the Marianas Trench.  From even the earliest explorations the large crustacean, the amphipod Hirondellea gigas, was observed.  Scientists have even isolated bacteria from its body.  Indeed, larger organisms have been found at the bottom of several trenches (see photo below).  A specimen of sea anemone of the genus Galatheanthemum, a worm from the genus Macellicephaloides, an isopod crustacean of the genus Macrostylis, and a sea cucumber Myriotrochus bruuni are all known from the deepest trench on earth and reported back in the 1970’s by Torbin Wolff (of Haka fame).

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Cameron stated after his dive the necessity of returning to the deepest point in the ocean, the Challenger Deep, once again to explore.  I could not agree more. Our understanding of this trench, like much of the deep, is rudimentary.  We only have a partial glimpse of the life that existing there. However, we do know that it is not a lifeless void.  A wealth of life exists at Marianas Trench. You just have to know how to loo for it.

Dr. M (1628 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, created to facilitate research to address fundamental questions in evolutionary science. He has conducted deep-sea research for 11 years and published over 40 papers in the area. He has participated in dozens of expeditions taking him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses mainly on marine systems and particularly the biology of body size, biodiversity, and energy flow. He focuses often on deep-sea systems as a natural test of the consequences of energy limitation on biological systems. He is the author and chief editor of Deep-Sea News, a popular deep-sea themed blog, rated the number one ocean blog on the web and winner of numerous awards. Craig’s popular writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web.





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3 comments on “Is Marianas Trench A Lifeless Void?
  1. Nice post and a good point. When it comes to Forbes, I think he often gets a bad press. Sure, in a summary of the azoic hypothesis just before his death in 1854, he described the deep sea as a place “where life is either extinguished or exhibits but a few sparks to mark its lingering presence.”

    BUT he went on to add:

    “Its confines are yet undetermined, and it is in the exploration of this vast deep-sea region that the finest field for submarine discovery yet remains.”

    He also noted the occurrence of new species not known from shallow water in his Aegean dredges, and commented that:

    “They were like the few stray bodies of strange red men, which tradition reports to have been washed on the shores of the Old World before the discovery of the New, and which served to indicate the existence of unexplored realms inhabited by unknown races, but not to supply information about their character, habits, and extent.”

    Looking at his words, I think Forbes regarded the azoic hypothesis as exactly that: a hypothesis to be tested. At the time, it was a projection of the pattern he had observed with depth in the Aegean, but I think his comments indicate that his mind was open to the possibility of that hypothesis being refuted by further exploration and discovery.

    So I’m always happy to defend him as a whipping boy, and would argue that he was following what we might call the “scientific method”. I don’t think that, in his regard, being “wrong” in science is a “mistake”.

      • I usually set my 1st Year students an assignment to research the contribution of a marine scientist who interests/inspires them, and they seem to choose Forbes as often as Wyville Thompson, Murray, Sars, Agassiz etc. Poor guy died at the age of 39, and didn’t get to see results from, for example, HMS Lightning, HMS Porcupine, or of course HMS Challenger, among many other expeditions of other countries.

        The azoic hypothesis lived on a bit further, though, in the view of the mid-water fauna, even after the Challenger expedition, as summarised by Henry Moseley in 1879:

        “Very possibly the pelagic animals do not range to any great depth, 100 or 150 fathoms, or less. It is quite possible that a vast stretch of water between the surface and the bottom is nearly or absolutely without life.”

        What strikes me reading the words of some of the 19th century deep-sea biologists, however, is how often they make points still echoed today. In particular, there’s the rallying call for exploration because the deep ocean is a vast unknown (e.g. “our knowledge of this vast and wonderful region is still in its infancy” – Sydney J Hickson, The Fauna of the Deep Sea, 1894).

        But of course we’ve come a very long way since Forbes, and perhaps now we should be emphasising, as Dr M does above, how much we do know, in addition to the unknown. The deep ocean can still surprise us with “unknown unknowns”, but physically there’s no part hidden to us any more, if we can find the will to investigate it. To me, the modern challenge is what to do with our ever-growing knowledge of the deep ocean, both in testing fundamental ideas in biology, and using our understanding to inform its stewardship. But I’m preaching to the choir here on that, I know! :)

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