Great Abyssal Diversity Among the Microscopic

ResearchBlogging.orgAn area the size of a coffee table on the deep-sea floor would yield hundreds of species.  A few species would dominate with numbers in the 10-100’s.  Yet most would be rare represented by a single lone individual. These latter species are the “rare biosphere” and one of the most conspicuous phenomena of the deep sea. One of the conundrums of the “rare biosphere” is how a species can be rare locally but found globally.  Imagine if Krispy Kreme donuts were found across the U.S. but there was only one per state. O’ the horror, but it illustrates the point nicely

Unfortunately  what we know of deep-sea diversity is based on bigger life like worms like snails, crustaceans, and echinoderms. Little is known about microbial diversity of the muddy ooze that characterize the immense deep-sea floor.  That is until now.  Microbial diversity on the abyssal plains is higher than we thought and dominated by the rare biosphere.

Radiolarians from Kunstformen der Natur (1904), plate 31 from Ernst Haeckel available on Wikimedia Commons

A new study in PNAS by Scheckenbach et al. documents the biodiversity of microbes across the South Atlantic.  Nearly 400 “operational taxonomic units,” shorthand for genetically distinctive organisms, were discovered.  For 73% of these organisms, no closely genetically related organisms are currently known.  Like many other deep-sea organisms, microbial communities are dominated by rare species represented by single to few individuals. And like other deep-sea species found over large areas of the seafloor, in this case over 1000’s of kilometers.

We gauge how well we have sampled an area by viewing a sampling curve, a plot of sampling effort versus the number of new species.  This allows us to determine whether we are likely to find more new species with increased sampling effort.  We hope these curves are “saturated” and that the answer to the previous question is no.  However, this is rarely the case with deep-sea studies and sampling curves rarely reach saturation.  The Scheckenbach et al. microbial study is no different and future sampling is likely to uncover hundreds of new species.

Overall this study challenges the idea of depauperate deep sea.  It will also shape how we strive to understand biodiversity of the deep sea, as hypotheses explaining these biodiversity patterns will have to account for both metazoans and microbes.
Scheckenbach, F., Hausmann, K., Wylezich, C., Weitere, M., & Arndt, H. (2009). Large-scale patterns in biodiversity of microbial eukaryotes from the abyssal sea floor Proceedings of the National Academy of Sciences, 107 (1), 115-120 DOI: 10.1073/pnas.0908816106

Dr. M (1729 Posts)

Craig McClain is the Assistant Director of Science for the National Evolutionary Synthesis Center, a National Science Foundation supported initiative. He has conducted deep-sea research for 20 years and published over 50 papers in the area. He has participated in and led dozens of oceanographic expeditions taken him to the Antarctic and the most remote regions of the Pacific and Atlantic. Craig’s research focuses on how energy drives the biology of marine invertebrates from individuals to ecosystems, specifically, seeking to uncover how organisms are adapted to different levels of carbon availability, i.e. food, and how this determines the kinds and number of species in different parts of the oceans. Craig’s research has been featured on National Public Radio, Discovery Channel, Fox News, National Geographic and ABC News. In addition to his scientific research, Craig also advocates the need for scientists to connect with the public and is the founder and chief editor of the acclaimed Deep-Sea News (, a popular ocean-themed blog that has won numerous awards. His writing has been featured in Cosmos, Science Illustrated, American Scientist, Wired, Mental Floss, and the Open Lab: The Best Science Writing on the Web. His forthcoming book, Science of the South (, connects cultural icons of South such as pecan pie with the science behind them.

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