ARCHIVE: 25 Things You Should Know About the Deep Sea: #4 The Deep Sea Has Extremely High Species Diversity

It had been assumed for a century before that the deep-sea fauna was depauperate, and prior to then that the great depths were essentially sterile. These ideas were largely a carry over from Edward Forbes in the late 1800’s, who proposed the azoic hypothesis for the deep sea. Interestingly, his idea was largely based on samples from the Aegean Sea now known to have relatively low densities of organisms compared to other deep-sea areas. The lack of deep-sea life was overturned by several later reports of deep-sea species attached to sounding lines and the dredging cruises of the H.M.S. Lighting, Porcupine, and Challenger. In 1968, Sander’s comparative study of marine benthic diversity, showed that bathyal diversity exceeded coastal diversity in the temperate zone and approached shallow-water tropical diversity. The development and deployment of more effective sampling gear has indicated that diversity is probably even higher than Sanders estimated, potentially rivaling that of tropical rain forests. On relatively small scales, the number of species coexisting in the deep sea is surprisingly high, exceeding 300 macrofaunal species m-2 at bathyal depths in the western North Atlantic. The greater diversity in what appears to be a more homogeneous environment has long perplexed marine ecologists and remains a major theoretical challenge. Numerous hypotheses have been proposed including competition, facilitation, predation, disturbance, productivity, environmental heterogeneity and patch dynamics.

Further papers on deep-sea diversity (in no particular order)

Etter RJ, Grassle JF (1992) Patterns of species diversity in the deep sea as a function of sediment particle size diversity. Nature 360:576-578

Gray JS (1994) Is deep-sea species diversity really so high: species diversity of the Norwegian continental shelf. Marine Ecological Progress Series 112:205-209

Lambshead PJD, Boucher G (2003) Marien nematode deep-sea biodiversity-hyperdiverse or hype? Journal of Biogeography 30:475-485

Cronin TM, Raymo ME (1997) Orbital forcing of deep-sea benthic species diversity. Nature 385:624-627

Gage JD, Tyler PA (1991) Deep-Sea Biology: A Natural History of Organisms at the Deep-Sea Floor, Vol. Cambridge University Press, Cambridge

Gage J, Lambshead PJD, Bishop JDD, Stuart CT, Jones NS (2004) Large-scale biodiversity pattern of Cumacea (Percarida: Crustacean) in the deep Atlantic. Marine Ecological Progress Series 277:181-196

Gooday AJ, Bett BJ, Shire R, Lambshead PJD (1998) Deep-sea benthic foraminiferal species diversity in the NE Atlantic and NW Arabian sea: a synthesis. Deep-Sea Research II 45:165-201

Snelgrove PVR, Smith CR (2002) A riot of species in an environmental calm: the paradox of the species-rich deep-sea floor. Oceanography and Marine Biology 40:211-242

Rex MA (1981) Community structure in the deep-sea benthos. Annual Review of Ecology and Systematics 12:331

Rex MA (1983) Geographic patterns of species diversity in the deep-sea benthos. In: Rowe GT (ed) The Sea. Wiley, New York, p 453-472

Stuart CT, Rex MA, Etter RJ (2003) Large-scale spatial and temporal patterns of deep-sea benthic species diversity. In: Tyler PA (ed) Ecosystems of the World-Ecosystems of Deep Oceans. Elsevier, Amsterdam

Levin LA, Etter RJ, Rex MA, Gooday AJ, Smith CR, Pineda J, Stuart CT (2001) Environmental influences on regional deep-sea species diversity. Annual Review of Ecology and Systematics 32:51-93

Gage J (1998) Why are there so many species in deep-sea sediments. Journal of Experimental Marine Biology and Ecology 200:257-286

Sanders HL (1968) Marine benthic diversity: a comparative study. American Naturalist 102:243-282

Grassle JF (1989) Species diversity in deep-sea communities. Trends in Ecology and Evolution 4:12-15

Rex MA, McClain CR, Johnson NA, Etter RJ, Allen JA, Bouchet P, Waren A (2005) A source-sink hypothesis for abyssal biodiversity. American Naturalist 165:163-178

Dr. M (1801 Posts)

Craig McClain is the Executive Director of the Lousiana University Marine Consortium. 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. Additionally, Craig is obsessed with the size of things. Sometimes this translated into actually scientific research. 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.