Scientists say up to 90 percent of ocean species are still unknown, and every expedition proves it

Marine researchers working with a global effort called Ocean Census say that despite centuries of exploration, up to 90 percent of the species living in the world’s oceans have never been formally described by science. The estimate is not a guess pulled from old textbooks; it comes directly from scientists running expedition after expedition and finding that new, undocumented life turns up almost everywhere they look.

Why the 90 Percent Estimate Holds Up

The figure reflects just how little of the deep ocean has ever been directly sampled. Most of the seafloor sits below the reach of sunlight, at depths that require specialized submersibles and remotely operated vehicles to reach at all, and even well-funded research programs can only cover a tiny fraction of that terrain in a given year. Oceans cover more than 70 percent of the planet’s surface, yet the tally of formally described marine species remains a small slice of what researchers believe is actually down there, which is why the 90 percent figure has persisted across successive waves of ocean exploration rather than shrinking as expected.

Ocean Census, a collaborative program backed by The Nippon Foundation and the ocean-exploration nonprofit Nekton, along with partners including the Schmidt Ocean Institute, was built specifically to close that gap faster than the traditional pace of marine taxonomy allows, according to the program’s own account of its work. Rather than leaving discovery to individual labs working in isolation, the program pools ships, submersibles and taxonomists from multiple institutions into coordinated expeditions aimed squarely at finding and describing species before they disappear unrecorded.

Thirteen Expeditions in a Single Survey Period

Between April 2025 and March 2026, Ocean Census researchers ran 13 separate expeditions and nine species discovery workshops, gatherings where taxonomists from around the world examine specimens together to speed up formal identification, as reported in a detailed account of the survey period. That combined effort produced 1,121 species new to science in a single year, a pace that program leaders describe as evidence the 90 percent estimate is not exaggerated so much as it is a realistic reflection of how much remains to be catalogued. The workshops themselves matter almost as much as the expeditions: bringing taxonomists together in person to jointly examine specimens compresses a review process that, done individually, has historically dragged on for years per organism.

Dr. Michelle Taylor, Head of Science for Ocean Census, has said the program is in “a race against time to understand and protect ocean life,” warning that too many species stay undocumented for years because the formal description process moves too slowly relative to the pressures facing marine ecosystems. That urgency is part of why the program measures its own success not just in total species counted, but in how much it can shorten the gap between a specimen’s first collection and its official scientific recognition.

Nearly Every Expedition Turns Up Something New

What has struck program scientists is how consistently new species appear once an expedition reaches an under-sampled habitat, whether that is a cold-water seamount, a deep reef system or a little-visited stretch of continental slope. The most recent survey period alone produced creatures spanning wildly different branches of the animal kingdom: a chimaera known informally as a ghost shark, a carnivorous sponge nicknamed the “death ball” for how it traps small crustaceans, ribbon worms, sea cave shrimp and previously unrecorded corals and sea pens.

That range matters because it undercuts the idea that undiscovered ocean life is limited to a few exotic categories of deep-sea oddities. Instead, the pattern researchers describe is closer to the reverse: nearly any unstudied patch of ocean, at nearly any depth, is likely to contain organisms that have never been assigned a scientific name, simply because so little of the ocean floor has ever been surveyed closely enough to know what lives there.

The Bottleneck Is Description, Not Discovery

Collecting a specimen is often the easy part. Before a creature counts as an officially new species, it has to clear a formal review that includes comparison against museum records and genetic databases, a detailed physical description, and publication in the scientific literature, a process that historically could take years for a single organism handled by one small team. Pooling specimens and taxonomic expertise across an entire program, the way Ocean Census does, is the structural change behind totals reaching into the thousands within a single year rather than the handful that used to be typical.

Even so, the backlog is enormous. Program leaders have been explicit that many species collected during past expeditions are still working their way through that review pipeline years later, which means the true number of species already sitting in specimen collections, waiting on formal description, is almost certainly larger than any single year’s published tally suggests.

What the Gap Means for Ocean Conservation

The scale of the unknown carries real consequences beyond scientific bookkeeping. A species that has never been formally described cannot be assessed for conservation status, tracked for population decline, or factored into decisions about which habitats deserve protection. As deep-sea mining proposals, fishing pressure and warming waters all reshape ocean ecosystems, researchers involved in Ocean Census argue that closing the 90 percent gap is no longer a purely academic exercise, since species can disappear from a habitat before anyone has confirmed they existed there at all. Every new expedition that turns up dozens of undocumented organisms is, in that sense, also a reminder of how much marine life may already be at risk without ever having been counted.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.

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