What are deep-sea canyons, seamounts, and continental slopes?
Carved over millions of years, deep-sea canyons, continental slopes, and seamounts shape some of the most dramatic underwater landscapes on Earth. Canyons cut into the edges of continents, plunging thousands of feet below the surface. Seamounts—underwater mountains formed by ancient volcanoes—rise from the seafloor, often teeming with life. The continental slope forms the steep transition between the shallow continental shelf and the abyssal plain.
Several sanctuaries across the National Marine Sanctuary System protect deep-sea canyons, seamounts, and continental slope habitats that support some of the ocean's most mysterious and diverse ecosystems. Along the West Coast, these include parts of Channel Islands, Chumash Heritage, Monterey Bay, Greater Farallones, Cordell Bank, and Olympic Coast national marine sanctuaries, where submarine canyons and steep slopes harbor deep-sea corals, sponges, and fishes. In the Gulf, Flower Garden Banks National Marine Sanctuary contains both shallow coral reefs and deeper slope habitats that extend into the twilight zone. Across the Pacific Islands, the volcanic ridges and seamounts of the National Marine Sanctuary of American Samoa and Papahānaumokuākea National Marine Sanctuary reveal thriving deep-ocean communities shaped by geologic forces.
Why are deep-sea canyons, seamounts, and continental slopes important?
These deep-water habitats support extraordinary biodiversity and play vital roles in the ocean's health. Their rugged terrain creates countless micro-habitats that shelter cold-water corals, sponges, crabs, and deep-sea fishes. Upwelling currents along canyon walls and seamount slopes bring nutrient-rich waters to the surface, fueling plankton blooms and sustaining life far above.
Deep-sea canyons also serve as migration corridors for whales, seabirds, and other pelagic species. The coral and sponge communities that cling to rocky outcrops provide nursery habitat for commercially valuable fish, while the sediments of continental slopes help store "blue carbon," locking away carbon that might otherwise contribute to a fast-changing ocean.
What threats do deep-sea habitats face?
Despite their depth and distance from shore, deep-sea canyons, slopes, and seamounts face increasing pressure from human activity. Deep-sea fishing, bottom trawling, oil and gas exploration, and even the potential for seabed mining can damage or destroy slow-growing corals and sponges that may take centuries to recover.
Warming waters, changing currents, and decreasing oxygen levels are also altering deep-ocean conditions. Sanctuaries help safeguard these fragile systems by limiting destructive practices, supporting long-term monitoring, and conducting deep-sea research expeditions that inform conservation and sustainable management.
Deep-Sea Habitat Connectivity
The canyons, slopes, and seamounts of America's treasured national marine sanctuaries form an interconnected network that supports marine life from surface to seafloor. Safeguarding these remote environments ensures that the ocean's "blue heart" continues to regulate climate, sustain biodiversity, and inspire discovery.
Deep-Sea Species Spotlights
Each canyon, slope, and seamount hosts a world of specialized organisms adapted to life in the dark. The exact species found in these deep-sea habitats can vary widely from one region to another, shaped by differences in temperature, depth, and geology—yet some species, such as certain deep-sea corals and brittle stars, are found across multiple sanctuaries. Together, these communities demonstrate the remarkable resilience and biodiversity of life in our ocean's hidden realms.
Bubblegum Coral (Paragorgia arborea)
Where it lives: Bubblegum coral thrives in cold, deep waters where strong currents deliver a steady flow of plankton. It typically grows on hard, rocky surfaces along continental slopes, seamounts, and canyon walls between 650 and 4,300 feet (200–1,300 meters). These conditions occur in several national marine sanctuaries, including Monterey Bay, Greater Farallones, Chumash Heritage, and Channel Islands national marine sanctuaries.
Why it matters: With its vivid pink, branching structure, bubblegum coral provides critical three-dimensional habitat for brittle stars, crabs, shrimp, and deep-sea fishes. These colonies grow slowly—sometimes taking centuries to reach their full size—and are easily damaged by bottom-contact fishing gear or seafloor disturbance. Protecting them helps preserve the intricate architecture that supports entire deep-sea communities.
Deep-Sea Glass Sponge Garden (Hexactinellid Sponges)
Where it lives: Glass sponges inhabit cold, deep waters where strong currents flow across hard seafloor surfaces such as rocky outcrops, canyon walls, and seamount slopes. These stable, high-oxygen environments provide the perfect conditions for their delicate silica skeletons. Within the National Marine Sanctuary System, they are found in places such as Cordell Bank, Monterey Bay, and Olympic Coast national marine sanctuaries, as well as in deep volcanic ridges and seamount slopes of National Marine Sanctuary of American Samoa and Papahānaumokuākea National Marine Sanctuary.
Why it matters: These "glass sponges" form intricate reef-like structures that filter vast amounts of seawater and provide habitat for invertebrates and fish. Their skeletons grow slowly and are extremely fragile, making them vulnerable to disturbance from trawling gear, cables, or other bottom-contact activities. Protecting sponge gardens helps preserve some of the oldest and most delicate habitats in the deep sea.
Deep-Sea Octopus (Order Octopoda)
Where it lives: Deep-sea octopuses inhabit cold, oxygen-rich waters as far as 10,000 feet (3,000 meters) deep. They are most often found on rocky canyon walls, volcanic slopes, and boulder-strewn seafloors that offer crevices for shelter and egg-laying. Some species, like the dumbo octopus (Grimpoteuthis spp.), swim gracefully through the water column, using their fin-like "ears" to propel themselves. Within the National Marine Sanctuary System, deep-sea cephalopods have been observed during remotely operated vehicle surveys in Monterey Bay, Channel Islands, Greater Farallones, Papahānaumokuākea, and Flower Garden Banks national marine sanctuaries, among others.
Why it matters: Deep-sea octopuses exemplify extraordinary adaptations to life under extreme pressure and near-freezing temperatures. Some species, such as Graneledone boreopacifica and Muusoctopus spp. are known for long brooding periods—guarding their eggs for years in stable, oxygen-rich canyon waters. Others, like the dumbo octopus, use fin-like "ears" to swim gracefully through the dark midwater realm, hovering effortlessly while they hunt. The presence of these eight-armed predators and scavengers signals healthy deep-ocean ecosystems that support complex food webs.
Crinoids and Sea Stars (Echinoderms)
Where they live: Different species of crinoids and sea stars are found on rocky slopes and canyon walls in many national marine sanctuaries with deep-sea habitats, including National Marine Sanctuary of American Samoa, and Olympic Coast, Channel Islands, and Flower Garden Banks national marine sanctuaries.
Why they matter: Crinoids—sometimes called feather stars—use their feathery arms to capture drifting plankton, filtering nutrients from the surrounding water. Brittle stars, close relatives of true sea stars, cling to corals and sponges, helping form complex reef communities that shelter countless invertebrates and fish. Together, these echinoderms serve as indicators of strong currents, healthy nutrient flow, and thriving deep-sea ecosystems.
