Five Reasons Seamounts Matter

By Sophia Barwegen, Val Brown, Andy Collins, and Sarah Head

May 2025

Just like on land, there are vast mountains that lie deep beneath the ocean’s waters. Seamounts are underwater mountains that rise at least 3,300 feet (1,000 meters) from the surrounding seafloor, most of which include the remains of extinct volcanoes. These submarine mountains can be found in every ocean basin and serve an essential role in supporting biologically rich deep-sea ecosystems. Think of them like the underwater version of a coral reef or a kelp forest—critical foundation habitats where everything from deep-sea corals and sponges to commercially important fish and migratory species converge.

Several seamounts lie within the boundaries of your national marine sanctuaries, such as in Pāpahānaumokuākea, American Samoa, and Monterey Bay, which provide unique protections from 21st century challenges. Here are five reasons why seamounts are vital to our ocean and the national marine sanctuaries that safeguard them:

1. Seamounts Support Many Deep-Sea Species and Habitats

Seamounts are like ‘oases’ in the deep sea, serving as a gathering space for a variety of different organisms. In the cold, dark, and highly pressurized abyss of the sea, seamounts are biodiversity hotspots that are often teeming with life. As the slope of the seamount increases, deep-sea currents are forced upward, bringing nutrient-rich water that attracts a wide variety of species—from plankton to lobsters, and even sharks and whales. This productivity benefits the entire water column, not just the deep sea.

a spiny red sea star climbs on the limb of a coral in the deep sea — A predatory sea star slowly works its way up a bamboo coral on an unnamed seamount in the Pacific Islands region. Photo: NOAA

yellow, white, and red corals on the edge of a rocky structure in the deep sea — A high-density coral community seen living on boulders near the summit of the seamount explored during Dive 04 of the Beyond the Blue Mission in Papahānaumokuākea. Photo: NOAA

Corals and sponges serve as key species in the ecosystem, offering both nourishment for predators and shelter that supports a wide variety of marine life, including crabs, squat lobsters, and sea stars. The rugged terrain of seamounts creates small crevices that provide refuge for creatures like fish and octopuses.

Volcanic features, like hydrothermal vents and lava flows, introduce additional nutrients and alter the habitability of some sites, allowing for more life to recruit. The bacteria that live in these areas use chemicals, rather than sunlight, to create energy—a process called chemosynthesis. These bacteria form the base of a surprisingly diverse deep-sea community in a place that otherwise appears empty and lifeless. Unlike plants and algae that rely on sunlight to make food, chemosynthetic bacteria produce sugars through chemical reactions. In turn, they become food for animals such as shrimp, tubeworms, crabs, and fish.

a robotic arm with a sensor gathers data from the water released from a hydrothermal vent in the deep sea — Researchers aboard exploration vessel (E/V) *Nautilus* investigate a hydrothermal vent with a remotely operated vehicle (ROV) in National Marine Sanctuary of American Samoa. Credit: OET/NOAA

2. Seamounts Tell Stories of Our Planet’s History and Future

Most seamounts are formed by underwater volcanic activity, either at “hot spots”—where molten rock rises from deep within the Earth—or along the edges of tectonic plates. Seamounts can form in other ways too, but these are the most common.

Vailulu’u Seamount is an active hotspot volcano located approximately 100 miles east of Tutuila, American Samoa’s largest island. This seamount is believed to be the current expression of the hotspot that formed the Samoan archipelago. In 2005, during the second ever mapping of Vailulu’u Seamount, scientists discovered a volcanic cone, named Nafanua, had formed inside the caldera of the seamount. This volcanic activity, as well as the mapped changes of Vailulu’s caldera, suggest the seamount is growing, and may one day result in the formation of a new island.

A map of the volcanic islands over the Samoan Hotspot — The five volcanic islands of American Samoa (Tutuila, Aunuʻu, Ofu, Olosega, and Taʻū), as well as its neighbor islands in Samoa (Upolu and Savai'i), all formed over the Samoan Hotspot, which is currently located directly below Vailuluʻu Seamount. Image: Herrera et al., 2023

a bathymetric heatmap of a seamount that shows shallower parts of the feature in red and deeper parts in dark blue — Vailulu’u Seamount was first mapped in 1999 and then again by expeditions that periodically returned to the region over the next twenty years. The summit of Vailuluʻu presently lies at a depth of about 2,000 feet (600 meters). Image: Ocean Exploration Trust

In Pāpahānaumokuākea, the Liliʻuokalani Ridge Seamounts formed through hotspot volcanism and tectonic plate movement. This seamount chain was created during the mid to late Cretaceous period, between about 143 and 66 million years ago. At that time, the Pacific Plate was moving more to the north than it is today—a shift that can be seen in the angle of the Liliʻuokalani Ridge compared to the Hawaiian Ridge. By studying these seamounts and the clues they leave on the seafloor, scientists gain insight into Earth’s dynamic geological processes over millions of years.

Davidson Seamount, located about 75 miles off the coast of Central California in Monterey Bay National Marine Sanctuary, was once an active volcano though it went extinct several million years ago. This massive submarine mountain is one the largest seamounts in the waters of the United States at 26 miles long and 9 miles wide and was added to the sanctuary back in 2008 due its historical significance and sensitive habitats, including deep-sea corals which are essential to our ocean’s health.

a map of the region around Hawaii including Papahānaumokuākea and the Liliʻuokalani seamounts — Map showing the location of the Liliʻuokalani seamounts. Image: Ocean Exploration Trust

3. Seamounts Are Places of Scientific Discovery

We are still learning so much about the world around us and seamounts are full of interesting discoveries. Because seamounts lie deep beneath the ocean’s surface, scientists rely on advanced technology to explore them. At NOAA, we use a range of underwater robots to study these towering underwater mountains. One type is autonomous underwater vehicles (AUVs), which are pre-programmed to follow a path while collecting valuable data using onboard sensors and cameras. Another key tool is remotely operated vehicles (ROVs), which are connected to a ship via long cables and piloted from the surface. ROVs can be outfitted with video cameras, lights, sensors, robotic arms, and collection chambers to gather deep-sea samples.

a robot in the deep sea collecting a rock for the sea floor — The seamount explored during Dive 10 of the Beyond the Blue mission in Papahānaumokuākea is of unknown age, so the team worked to collect geological samples that can be used to determine the provenance of this seamount chain. Here, the arm of remotely operated vehicle Deep Discoverer is used to collect a rock sample. Photo: NOAA

ROVs have aided researchers in discovering that due to their isolation, seamounts are home to a wide array of organisms, some of which are endemic—species found nowhere else on the planet. In fact, it’s estimated that more than 30% of species found on some seamounts fall into this category. On an expedition aboard NOAA ship Okeanos Explorer, scientists discovered a brand new sponge species that resembles the beloved space alien from the movie “E.T. The Extra Terrestrial”. This glass sponge, Advenhena magnica, has only been seen on a seamount near Johnston Atoll. The discovery of new species, like this one, helps scientists garner a better understanding of deep-sea biodiversity and how species are interconnected.

In addition to visual surveys and specimen collection, scientists are also using a technique called environmental DNA (eDNA) sampling. This method involves filtering water samples—often gathered by an ROV—that contain genetic material shed by marine organisms. Analyzing eDNA allows scientists to detect species without having to see or capture them, making it a powerful tool for studying life in the deep.

three young adults in blue lab coats filtering water — Explorers-in-Training Rebecca Ruiz, Rose Leeger, and Ranna Zahabi filter water samples for environmental DNA collection during the Seascape Alaska 2: Aleutians Deepwater Mapping expedition. Photo: NOAA Ocean Exploration, Seascape Alaska

During the 2024 E Mamana Ou Gataifale expeditions aboard E/V Nautilus in National Marine Sanctuary of American Samoa, NOAA deployed a suite of advanced vehicles—including the uncrewed surface vehicle DriX, the autonomous underwater vehicle Mesobot, and the Deep Autonomous Profiler—to comprehensively study biodiversity throughout the water column. Together, these technologies collected a wide range of environmental data, including extensive eDNA samples that will support the most thorough assessment of pelagic biodiversity ever conducted in American Samoa.

Mapping the seafloor is another essential aspect of deep-sea research. Using multi-beam sonar and other high-resolution mapping tools, scientists can reveal the shape and structure of unexplored seamounts. This not only guides safer and more efficient exploration but also helps identify key habitats worth protecting and studying further.

4. Seamounts are vital feeding, breeding, and nursery areas

Seamounts are crucial stopovers for migratory species. Their upwelling currents bring nutrients to the surface, creating rich feeding grounds for fish, marine mammals, and seabirds. Many commercially important fish species—like tuna, orange roughy, and alfonsino—gather around seamounts for spawning and feeding, making them valuable but vulnerable fishing areas.

Mother octopuses rely on Davidson Seamount’s thermal springs to brood their eggs. In 2018, researchers from Monterey Bay National Marine Sanctuary and Ocean Exploration Trust discovered thousands of deep-sea octopuses nesting near “shimmering” waters at the base of the seamount—an effect caused by warm and cold water mixing. Follow-up ROV dives revealed that water from the cracks and crevices of this octopus garden was 51°F, about 16 degrees warmer than surrounding waters.

The pearl octopus (Muusoctopus robustus), one of the species found here, typically takes five to eight years to hatch in cold deep-sea temperatures. But at this warm-water seep, eggs hatched in less than two years. This shorter brooding time boosts both reproductive success and hatchling survival.

Pearl colored octopuses with the heads down between cracks on the seafloor. — Mother octopuses brooding their eggs at Davidson Seamount’s octopus garden in Monterey Bay National Marine Sanctuary. Image: Ocean Exploration Trust/E/V *Nautilus* and Chad King/NOAA

During the 2024 E Mamana Ou Gataifale expeditions, researchers spent an extended period at the Vailulu’u seamount and noted a higher density of marine mammals there—many of which seemed to be actively feeding. Sightings included pilot whales, false killer whales, and humpback whales. eDNA samples collected in the area will help confirm the presence of marine mammals at these sites, and scientists hope to conduct additional surveys during future expeditions to further explore the link between seamounts and marine mammals.

5. Seamounts Play an Essential Role in Oceanic Circulation and Nutrient Cycling

In addition to being places of new species discovery, studying seamounts also helps to increase our understanding of the movement of oceanic currents. Seamounts tower above the seafloor acting as an obstacle to currents and even are known to have their very own circulation systems. For example, Davidson Seamount may influence local ocean circulation by altering the flow of the California Current and California Undercurrent. The seamount’s topography can generate strong currents and even transient Taylor Columns—rotating water features that trap nutrients and plankton above the seafloor. This enhanced productivity may help explain why researchers have observed a greater abundance of marine mammals and seabirds at/near Davidson Seamount.

Upwelling occurs when nutrient-dense waters from the ocean’s depths replace the warmer surface waters which move offshore. The steep slopes of seamounts play a crucial role in the vertical mixing of water and nutrients in upwelling. This infusion of nutrients fuels phytoplankton blooms which is foundational for the sustenance of the open ocean ecosystem. Additionally, the introduction of metals and minerals such as iron, manganese, and sulfides from hydrothermal vents support chemosynthetic organisms. In the vast expanse of the open ocean, seamounts can act as an oasis for organisms seeking nourishment.

Safeguarding Seamounts in Our National Marine Sanctuaries

Seamounts might be out of sight, but their impact reaches your dinner plate, your medicine cabinet, and your local economy. Seamounts serve an essential role in a thriving ocean and support a range of organisms—from commercially-important tuna populations that fishermen rely on, to migratory whales and birds that eco-tourism businesses rely on.

According to the International Union for the Conservation of Nature, roughly 200,000 seamounts exist throughout the world, and over 30,000 seamounts are known to exist in the Pacific Ocean alone, but less than 300 of the world’s seamounts have been explored and relatively few are protected. NOAA’s Office of National Marine Sanctuaries researches and monitors seamounts within the boundaries of America’s protected underwater parks by studying their geological history and their complex deep-sea ecosystems in order to increase our understanding of the role that these underwater mountains play in the greater marine environment.

The National Marine Sanctuaries Act enables research on seamounts by protecting these unique deep-sea features within sanctuary boundaries and supporting the tools needed to explore them—like remotely operated vehicles, underwater mapping, and imaging technologies. By fostering collaboration among scientists, universities, Indigenous communities, and other partners, sanctuaries serve as living laboratories where researchers have the tools and access necessary to study seamount geology, biodiversity, and ecosystem function, and share their findings with the public.

The seamounts found within the waters of national marine sanctuaries, such as at Monterey Bay, Papahānaumokuākea, and National Marine Sanctuary of American Samoa offer excellent opportunities for continued exploration and discovery, and are safeguarded for years to come.

Sophia Barwegen is the Coastal Discovery Center coordinator and Southern Region liaison for NOAA’s Monterey Bay National Marine Sanctuary.

Val Brown is the research coordinator at National Marine Sanctuary of American Samoa

Andy Collins is an education coordinator and manages the Mokupāpapa Discovery Center for Papahānaumokuākea

Sarah Head is a research scientist at National Marine Sanctuary of American Samoa

Rachel Plunkett is the content manager and senior writer/editor for NOAA’s Office of National Marine Sanctuaries