Far below the rolling waves, a vast network of towering undersea mountains is emerging as one of the planet’s most important havens for marine predators – especially sharks.
New research shows these ancient volcanic peaks, known as seamounts, host extraordinary concentrations of life, making them critical strongholds for threatened species.
Seamounts are dramatic formations that rise at least 1,000 metres from the ocean floor, sometimes even piercing the surface to form remote islands.
Although more than 100,000 are believed to exist worldwide, less than a fraction of a percent has been studied in detail. As deep-sea expeditions accelerate, scientists are discovering that these submerged mountains are biodiversity hotspots unlike any other.
“Over the past two decades, an unprecedented number of volcanic seamounts have been mapped,” says Ali Mashayek, climate dynamics expert at the University of Cambridge.
With each new survey, researchers uncover ecosystems packed with corals, crustaceans, turtles, rays, fish and, in particular, large predators.
One such discovery came near Ascension Island, a tiny volcanic outpost in the mid-Atlantic. Marine scientist Sam Weber and his research team spent more than two weeks surveying seamounts roughly 300 kilometres offshore.
Ascension, Weber explains, is simply the exposed peak of a much larger volcanic chain stretching hundreds of kilometres across the ocean floor.
Weber’s team targeted three seamounts, including two shallow peaks named Grattan and Young, which rise to just 100 metres below the surface. Working alongside commercial fishers aboard a small longline vessel, the scientists tagged dozens of sharks while documenting the species present.
The results were striking – the Southern Seamounts contained 41 times more shark biomass than surrounding open ocean areas. Overall predator diversity was five times higher, and total biomass of sharks and large fish was 30 times greater compared to nearby waters. Threatened species, including silky sharks, were notably abundant, alongside commercially valuable tuna.
“Sharks, whether deep-sea or migratory, consistently gather around seamounts in every major ocean,” says Lydia Koehler, a marine governance specialist at Plymouth University. But the reasons behind this phenomenon remain only partly understood.
Several theories explain why animals converge on these isolated peaks. Some species may use seamounts as navigational landmarks, guided by their distinctive magnetic signatures – imprints formed when volcanic rock cools and locks in the Earth’s magnetic field. Others may visit for shelter, feeding grounds, or social interactions.
Scientists also describe two broader ecological models – the oasis hypothesis, where seamounts generate or concentrate nutrients that support dense food webs, and the hub hypothesis, which sees them as gathering points for predators returning from distant feeding grounds.
Oceanographers have long known that seamounts influence water flow. When deep currents collide with the steep slopes, they push cold, nutrient-rich water upwards – a process that can trigger bursts of plankton growth and, subsequently, attract higher predators. Mashayek’s research suggests this mixing effect is so powerful that seamount turbulence contributes to nearly one-third of global deep-ocean circulation.
But Weber’s work near Ascension found something different; rather than increased plankton, the surge in predators was driven by mesopelagic species rising from the twilight zone, creating concentrated pockets of prey around the summits.
These ecosystems, scientists warn, are extremely vulnerable. For decades, seamounts have been targeted by industrial fisheries, especially bottom trawlers that scrape the seabed and destroy fragile coral and sponge habitats. Koehler calls bottom trawling “one of the most destructive fishing practices in the world,” with impacts that can take centuries to repair.
Although global momentum is building to restrict harmful fishing practices, including an international call to phase out bottom trawling on seamounts by 2026, researchers say more protection is needed.
