San José, Costa Rica, since 1956

The deep down on seamounts

President Laura Chinchilla has garnered accolades for the recent creation of the Seamounts Marine Management Area around Isla del Coco, Costa Rica’s legendary “Treasure Island” and national park nearly 600 kilometers off the Pacific coast (TT, March 18). The 964,000-hectare marine protected area is named after mountains under the sea in the region. So what’s up with seamounts? Here’s the deep down on these undersea masses.

Seamounts rise from the ocean floor around the world. There are so many that worldwide total estimates may differ by more than 100,000. And that’s just for the big ones. There are tens of thousands of known giant mountains that have erupted to over 1,000 meters above the bottom. Volcanic eruptions are the only way you get a seamount.

Seamounts are thought to collectively cover an area of earth well over double the size of all the world’s wetlands, sea grass beds, coral reefs, mangroves and beaches put together. Put another way, these mountains under the sea make up one of the largest life zones on earth. People will still be discovering seamounts for a long time.

When magma rises up though areas of the earth’s crust, the place is appropriately called a hot spot. As the earth’s crust sails by over the hot spot, seamounts are created. The Hawaiian Islands are perhaps the most famous example of seamounts forming over a hot spot and, over millions of years, drifting hundreds of kilometers away as new seamounts form.

The Galápagos Islands are also formed from a hot spot. These undersea mountains drift northeast over the eons, riding on the Cocos tectonic plate. Isla del Coco seems to have been formed over the Galápagos hot spot, and, being much older than the current Galápagos Islands, has sailed much closer to Costa Rica. Still older seamounts from the Galápagos hot spot may be the Osa and Nicoya peninsulas. These seamounts have pegged the continent, thus becoming part of the Costa Rican mainland. So there are people living in Costa Rica on seamounts right now.

But most seamounts are underwater and are inhabited by denizens of the deep, not humans. Seamounts are basically fish magnets. The structures provide nooks and crannies for life to bloom with a greater bioproductivity and biodiversity than in most other ocean areas.

Deep seamounts are often chock full of marine life, from whales and sharks to corals and sea stars. Certain seamounts are important gathering places for large pelagic animals. The hammerhead shark congregations of Isla del Coco National Park are perhaps the world’s most famous example of seamount big-animal attraction. We know about the hammerheads only because of divers. Divers have visited just a handful of seamounts in the world, so you have to wonder what other big-animal congregations are going on around all the other, undiscovered seamounts.

Deep-sea corals on seamounts give us even more to wonder about. The oldest animal in the world, a black coral by the name of Leiopathes, is thought to be 4,200 years old, and was discovered on a seamount. There are quite a few other deep seamount corals, like the excellently named gold corals, which are also thought to live for thousands of years.

Because less than 1 percent of the world’s seamounts have been explored, and most known ones are seriously damaged by commercial fishing or other resource extraction, protecting them is a brilliant idea. Mountains under the sea are well worth some conservation effort, as there are sure to be decades of discovery from this fantastic frontier.

So bottoms up to seamounts, and to the new protected area in Costa Rica bearing their name.

Email with contributions to The Big Blue, or check out for more information.

Comments are closed.