A marine expedition exploring previously unknown underwater volcanoes in the Indian Ocean Territories of Australia made an important biological discovery.
Aboard the research vessel RV Investigator, scientists mapped 22 seamounts around Christmas Island and the Cocos Islands. Their deep-water nets retrieved over one thousand marine species from lightless depths reaching 17,000 feet. Taxonomists already confirmed 149 species new to science, while hundreds of additional specimens await detailed anatomical and genetic laboratory analysis.
Mapping isolated underwater oases in the abyssal plain
Prior to this expedition, the depths of the abyssal waters around these remote islands remained a mystery of great oceanographic blank spots. Multibeam sonar arrays have been employed to create a map of isolated peaks of volcanoes of up to 43 square miles in size.
In order to collect marine organisms living in the vicinity of the seafloor, researchers deployed a 13-foot-long steel beam trawl with an armored cable of five miles in length. Slow towing of the gear made it possible to catch bottom-dwelling invertebrates and deepwater fish species.
Biological collection includes organisms with remarkable adaptive features for survival in conditions of intense hydrostatic pressure and absolute darkness. Among the species discovered are the abyssal greeneye fish, a new parasitic barnacle, and a very rare sea cucumber of the abyssal genus Oneirophanta.
Processing of the entire collection is a laborious task that requires years of microscopic and genetic laboratory examination. Scientists all over the world are already examining hundreds of provisional species in order to define their ranges and classification.
Uncovering an ancient shark graveyard in the abyssal deep
While carrying out the final trawling operations in the Cocos Abyssal Plain at depths exceeding 16,400 feet below sea level, paleontologists made an unexpected discovery. Scientists found about 1,000 fossilized shark teeth in one pass of a trawl on the seabed.
The fossil set covers over 22 million years of history of marine predators, starting from the Miocene epoch to the present days. It includes fossils of teeth of apex prehistoric predators such as the megalodon, as well as great white, mako, and tiger sharks’ ancestors.
Most of the teeth were covered with, or even totally embedded in, the dark polymetallic nodules. Such mineral formations form over millions of years through precipitation of metallic elements from seawater, using hard surfaces such as teeth as nuclei.
Paleontologists state that the ancient sharks did not inhabit lightless abyssal waters. Pelagic sharks inhabited upper water levels for millions of years, falling with their enamel-filled teeth to the ocean bottom upon dying.
Why ancient teeth accumulate on low-sediment abyssal floors
The geologic factors that contributed to the formation of this deposit of fossilized teeth are found in the special geology of the Cocos Abyssal Plain. In shallow water, the force of wave action, along with strong currents and fast coastal deposition, causes the shark teeth that fall to be covered up or destroyed within a short period of time.
However, the lack of turbulence in the environment of the abyssal plain results in very slow deposition of biological material, which only accumulates at the rate of several millimeters per thousand years. As a result, the shark teeth that fell were not buried by ocean debris for millions of years.
Eons of history as an apex predator
This serene abyssal setting gave rise to millions of years of evolutionary history of predators to be preserved in one concentrated geological database.
The survey results will provide important baseline information amid international talks regarding deep-sea polymetallic nodule mining and the warming of the world oceans. The discovery of slowly growing mineral nodules surrounding prehistoric teeth fossils makes clear that these deep benthic environments take millions of years to recover once disturbed.
Recording both current biodiversity as well as paleobiological information would be instrumental in helping resource managers create effective protected marine zones throughout Indian Ocean Territories. Creation of baseline information is vital in ensuring the slow-growing and vulnerable abyssal environments are adequately protected prior to any exploitation.
All the details of the study can be found here: O’Hara, T. D., Ahyong, S. T., Alderslade, P., Bray, D., Criscione, F., Davey, N., … & Williams, A. (2026). Faunal community ecology of central-eastern Indian Ocean Seamounts. Deep Sea Research Part II: Topical Studies in Oceanography, 105651.
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