Covering nearly two-thirds of the ocean and 99% of Earth’s habitable volume, the open ocean remains more than 80% unmapped even as overfishing has already removed 90% of large pelagic fish stocks.
The open ocean — waters beyond the continental shelf, unconnected to any coastline — covers about 64% of the ocean's total surface area and comprises nearly 99% of Earth's habitable space by volume. It remains the least explored major ecosystem on the planet.
More than 80% of the open ocean remains unmapped and unexplored, even as researchers continue to formally describe an average of over 2,300 new marine species per year, out of roughly 247,000 currently known valid marine species.
Source: World Ocean Assessment; marine taxonomy databases, 2025The high seas provide an estimated 80% of the fish caught for human consumption globally and carry out roughly half of the photosynthesis occurring on Earth via phytoplankton, making the open ocean a dominant regulator of both global fisheries and the planet's carbon cycle.
Because so much of the open ocean is unmapped, current biodiversity and decline statistics almost certainly understate the true scale of loss — species and habitats can disappear before they are ever formally documented. We treat open-ocean figures as a conservative floor, not a complete picture.
Because more than 80% of the open ocean remains unexplored, baseline biodiversity data is incomplete for large stretches of this ecosystem, and estimates of stock depletion are strongest for well-studied commercial species (tuna, billfish) and weakest for the vast majority of pelagic life that is not commercially fished.