Surveys of remote underwater mountains near Christmas Island and the Cocos Islands are transforming scientists’ understanding of one of the planet’s least explored ecosystems

Far beneath the surface of the Indian Ocean, in waters so deep that sunlight has long disappeared and pressure reaches crushing extremes, scientists have uncovered an extraordinary concentration of previously unknown marine life.

Researchers investigating remote seamounts around Christmas Island and the Cocos (Keeling) Islands have identified at least 149 species considered new to science, offering a rare glimpse into ecosystems that until recently represented little more than blank spaces on biological maps.

The findings emerged from extensive surveys conducted aboard Australia’s research vessel RV Investigator and have attracted renewed international attention following the publication of a detailed scientific assessment this year. Across two expeditions, researchers collected samples from 22 seamounts, the surrounding abyssal plains and waters around the two island groups, reaching depths from just 94 metres to 5,431 metres.

Scientists ultimately identified 1,059 taxonomic groups among the animals collected.

Only 495 — around 47% — could be matched confidently with species already formally described by science. Another 149, or roughly 14%, were classified as species new to science, while hundreds of additional specimens require further taxonomic investigation before researchers can determine whether they too represent undiscovered species.

The emerging inventory reads like a catalogue from an unfamiliar world.

Among the discoveries are previously undescribed black corals, marine worms, sea cucumbers, crustaceans and fish. Researchers highlighted a new sea cucumber belonging to the genus Oneirophanta, a previously unknown member of the greeneye fish family Chlorophthalmidae and an unusual parasitic barnacle from the genus Rhizolepas.

The importance of the discovery extends far beyond the number of new species.

The Indian Ocean covers roughly one-fifth of the world’s ocean surface, and about 90% of it is more than 1,000 metres deep. Yet its deep ecosystems remain considerably less studied than comparable environments in parts of the Atlantic and Pacific.

The central-eastern Indian Ocean has been particularly mysterious.

Before the recent voyages, scientists possessed relatively little biological information about the deep waters surrounding Christmas Island and the Cocos (Keeling) Islands, Australian territories lying between the Asian and Australian continents.

The expeditions effectively opened a new biological frontier.

At the centre of that frontier are seamounts — enormous underwater mountains, generally volcanic in origin, that rise from the seafloor without reaching the surface.

These formations can dramatically influence ocean currents, nutrient transport and marine habitats. Their slopes and summits provide hard surfaces on which corals, sponges and other organisms can establish themselves, creating ecological islands in otherwise vast expanses of deep ocean.

Some of the seamounts examined during the survey are tens of millions of years old and extend dozens of kilometres across.

Because individual underwater mountains may be geographically isolated from one another, populations living on them can evolve independently over extremely long periods. That isolation can encourage the development of species found nowhere else.

The surveys revealed just how biologically rich such environments can become.

Fish and decapod crustaceans accounted for some of the greatest species diversity among the collected specimens, while brittle stars were among the most abundant animals encountered overall.

But one of the expedition’s most striking discoveries was not alive.

Researchers encountered an area of seabed covered with approximately 1,000 fossilised shark teeth, a site that became informally known as the “Shark Tooth Graveyard.”

The teeth represented more than 20 million years of shark evolutionary history, according to researchers, effectively turning one small area of the deep ocean into a natural archive of predators that once moved through these waters.

Discoveries of this scale underline how incomplete humanity’s knowledge of the deep sea remains.

Taxonomists estimate that vast numbers of marine species have never been scientifically described, particularly in deep-water environments where research requires specialised vessels, remotely operated equipment and expensive expeditions.

Conditions below several thousand metres make exploration especially difficult.

There is no sunlight. Temperatures are low. Food can be scarce, and pressure is hundreds of times greater than at sea level.

Yet evolution has produced organisms capable of thriving under precisely these conditions.

Deep-sea species frequently display adaptations radically different from those seen in shallow-water ecosystems. Some possess highly sensitive sensory systems designed to function in darkness. Others survive on organic material falling from surface waters, exploit chemical energy near geological features or live in highly specialised relationships with other organisms.

Every expedition therefore has the potential not simply to add new names to the scientific record, but to reveal biological strategies that researchers have never previously encountered.

The Indian Ocean discoveries also carry an increasingly urgent conservation dimension.

Human influence is reaching environments once considered too distant to disturb.

Ocean warming, pollution, industrial fishing and the possible expansion of deep-sea mining are creating growing pressure on poorly understood ecosystems. Scientists warn that some habitats could be damaged before researchers have had an opportunity to document what lives there.

That problem is particularly important for seamounts.

Their concentrations of marine life can make them biologically valuable, but they can also attract commercial fishing activity. Some deep-water corals and other organisms grow extremely slowly, meaning damaged communities can require decades or centuries to recover.

The possibility of seabed mining introduces another layer of uncertainty.

Interest in extracting minerals from the deep ocean has increased as governments and companies seek metals used in batteries, renewable-energy systems and advanced electronics.

But scientists continue to debate the ecological consequences of disturbing deep-seafloor habitats that have evolved over geological timescales.

The newly catalogued biodiversity around Christmas Island and the Cocos Islands illustrates what may be at stake.

The discoveries are already expected to help Australian authorities manage marine protected areas surrounding the territories. CSIRO says the biological and seabed data collected during the voyages will provide a substantially stronger scientific foundation for conservation planning in the region.

There is also a deeper scientific significance.

Mapping where species live across different seamounts can help researchers understand how deep-ocean animals disperse, evolve and respond to geological barriers. It may reveal whether individual underwater mountains function as isolated biological islands or as stepping stones connecting populations across enormous stretches of ocean.

Such information could ultimately reshape models of marine evolution.

For centuries, exploration dramatically expanded humanity’s knowledge of terrestrial life. The deep ocean, however, remains one of the few regions of Earth where large-scale biological discovery is still routine.

Modern sonar can map the contours of underwater mountains, satellites can measure subtle variations in the ocean surface and remotely operated vehicles can descend kilometres beneath research vessels.

But technology has not eliminated the fundamental problem of scale.

The oceans cover more than 70% of the planet, and much of their deepest territory has never been directly observed in detail.

That is why the discovery of 149 previously unknown species is simultaneously remarkable and humbling.

It demonstrates an extraordinary abundance of life in a place scientists had barely investigated — while suggesting that the specimens already recovered may represent only a fraction of what remains hidden.

The seamounts of the Indian Ocean have therefore delivered more than a collection of unusual fish, corals and invertebrates.

They have provided another reminder that humanity is still conducting an inventory of its own planet.

And in the darkness several kilometres beneath the waves, that inventory is nowhere near complete.