Nautiluses live in the tropical waters of the western Pacific and Indian Oceans, drifting along steep coral reef slopes at depths between roughly 100 and 700 meters. They’re found near coastlines from the Philippines and Indonesia through Papua New Guinea, Palau, Fiji, Australia’s Coral Sea, New Caledonia, and as far north as southern Japan. Despite that broad range, individual populations are remarkably isolated from one another, separated by stretches of deep open ocean they cannot cross.
Geographic Range Across the Indo-Pacific
The chambered nautilus and its relatives occupy a belt of warm tropical and subtropical water stretching from the eastern Indian Ocean to the South Pacific. The countries with confirmed populations include Indonesia, the Philippines, Papua New Guinea, Palau, Fiji, Australia, New Caledonia, American Samoa, and India. Japan marks the northern edge of their range, where cooler waters limit how far they can spread.
Each population is effectively its own island. Nautiluses swim just above the seafloor and can’t survive below about 800 meters, where water pressure would crush their shells. They also avoid warm surface waters. That means any stretch of open ocean deeper than around 800 meters acts as an impassable barrier. A nautilus living off a reef in Palau has no way to reach a reef in Fiji, even though both populations belong to the same broad species group. This isolation is why scientists sometimes find distinct species on reefs only a few hundred kilometers apart. A 2023 study described three entirely new nautilus species from the Coral Sea and South Pacific alone.
The Reef Slopes They Call Home
Nautiluses don’t live on the colorful shallow reefs most people picture. Their habitat is the steep outer wall of coral reefs, the part that drops off sharply into deep water. These fore-reef slopes share a common profile across every known nautilus habitat: a near-vertical rocky wall in the shallower zone, transitioning to a more gradual, silty slope further down. At Osprey Reef in Australia’s Coral Sea, the seafloor plunges to 1,000 meters within just two kilometers of the exposed reef and reaches 1,700 meters within five kilometers.
The silty, muddy bottom at the base of these walls is where nautiluses do most of their feeding. Dead organisms drift down from the reef above, and crustaceans and their shed shells accumulate in the sediment. In Fiji, traps set on muddy substrate below the steep reef wall at 300 meters produced the best catch rates. In the Philippines’ Tanon Strait, where the bottom slopes more gently, nautiluses were caught at a steady rate from 61 to 320 meters across soft, silty ground. The pattern holds everywhere: nautiluses concentrate where scavenging opportunities are richest, typically on the gentler slopes just below the steepest part of the reef wall.
How Deep They Go
Nautiluses are not fixed at one depth. They migrate vertically through a range of roughly 130 to 700 meters, and their movement patterns are more complex than scientists initially thought. Early observations suggested a simple rhythm of shallow at night and deep during the day, but detailed tracking at Osprey Reef revealed something different.
During the day, nautiluses tend to split into two behaviors. Some rest nearly motionless at relatively shallow depths between 160 and 225 meters. Others actively forage in deeper water, between 489 and 700 meters. At night and around dawn, most individuals move to depths greater than 225 meters. Dawn is the time when the deepest dives, past 350 meters, are most common. Not every animal makes the deep trip every day, and the pattern likely varies between populations depending on local reef shape and food availability.
The absolute depth limit is set by their shells. A nautilus shell implodes at around 800 meters. That hard ceiling, combined with their intolerance of warm surface water (typically above about 25°C), confines them to a band of ocean that can be surprisingly narrow in vertical terms.
Palau’s Well-Studied Population
Palau hosts one of the best-documented nautilus populations in the world. The species found there, Nautilus belauensis, has been surveyed on Uchelbeluu reef near Koror going back to 1982. When researchers returned in 2015, they found catch rates almost unchanged: about 9.6 nautiluses per trap per day in 2015, compared to 9.76 in 1982. The sex ratio (roughly 1.7 males to every female) and the proportion of mature animals in the catch (86%) were also statistically the same across the three decades.
Palau’s population appears stable in part because the country has limited commercial harvesting. That’s not the case everywhere. Significant population declines have been documented in areas with targeted nautilus fisheries, including India, Indonesia, New Caledonia, and the Philippines.
The Rarest Nautilus: Allonautilus
Most nautiluses belong to the genus Nautilus, but there’s a second, far rarer group called Allonautilus. The crusty nautilus (Allonautilus scrobiculatus) was first seen alive in 1984 off Ndrova Island in Papua New Guinea, and then wasn’t spotted again for nearly 30 years. When researchers finally relocated it, they captured specimens using baited traps at about 183 meters depth.
Allonautilus appears to be restricted to a tiny geographic area around Papua New Guinea. Its shell is covered in a thick, fuzzy biological coating that distinguishes it immediately from its smoother relatives. Because nautilus populations are so isolated by deep water, species like this one can persist in a single location for millions of years without ever spreading to neighboring reefs.
Threats From the Shell Trade
Nautilus shells have long been sold as decorative objects, and the international demand has driven overharvesting in several countries. In 2016, the United States, Fiji, India, and Palau successfully proposed listing the entire nautilus family under CITES Appendix II, which means international trade is now regulated (though not banned) across more than 180 countries. The listing was designed to close a loophole where traders could mislabel shells from depleted species as coming from unprotected ones.
The core problem is biology. Nautiluses are slow-growing, late-maturing animals with low reproductive rates. A population that gets fished down doesn’t bounce back quickly. Despite the CITES protections, evidence of targeted fishing and trade continues in Indonesia, the Philippines, and China. Areas where fisheries have historically operated show measurably smaller populations compared to protected reefs like those in Palau.