Five countries signed an agreement this week committing to the protection of the Sargasso Sea, which occupies a vast stretch of the North Atlantic Ocean around Bermuda.

The Sargasso has long attracted the attention of conservationists and scientists because it hosts a rich diversity of wildlife, including leatherback sea turtles, humpback whales, and bluefin tuna. The animals eat and take shelter in a seaweed called sargassum, which floats in massive quantities in the area—some say it looks like a golden, floating rain forest—and gives the sea its name.

View Images NG Staff

Fishing and shipping traffic threatens to unravel this biologically rich ecosystem, on top of broader threats like climate change and ocean acidification.

The new nonbinding agreement on the Sargasso, called the Hamilton Declaration, is a first for the high seas.

Nations are entitled to govern the ocean 200 miles (322 kilometers) out from their shores. But beyond that, the high seas—which cover about half the surface area on Earth—are like the Wild West. Many nations use those waters for fishing or to extract resources like minerals, but no one country governs them.

Former chief scientist for the U.S. National Oceanic and Atmospheric Administration, Sylvia Earle has worked for years to set up some kind of governance framework for the high seas. "Half the world," she says, "is beyond national jurisdiction."

We spoke to Earle, a National Geographic explorer-in-residence, about what this latest agreement between Bermuda, the U.S., the Azores, Monaco, and the U.K. means for the future of the Sargasso.

View Images Sylvia Earle, pictured here on an expedition to the Sargasso Sea, calls the area a floating rain forest because of the diversity of animals found within its seaweed. Photograph by Shaul Schwarz, Getty

Tell us about the Sargasso Sea.

Its boundaries are actually liquid—it's defined by currents.

[It has] these floating islands of sargassum. Sargassum is two kinds of seaweed that are never anchored. Most seaweeds grow attached to something, but not these two kinds. They are a leafy, golden-brown, small, shrubby kind of seaweed that has distinctive gas-filled, berry-size floats that maintain the sargassum at the [ocean's] surface.

We refer to it as the floating, golden rain forest of the sea, populated by small, medium, and large animals. Some are only found there on the sargassum.

There are two great populations of freshwater eels that grow to maturity far inland in rivers [in North America and Europe], but then go to the Sargasso Sea on a remarkable journey to spawn.

The very young eels don't even look like eels—they look like transparent leaves with eyes. Ultimately, they transform into something that looks like an eel. They live about three years in the plankton until they find their way back to the rivers their parents came from.

If someone went out to this area, what would they see?

It's seasonally abundant. That is, you can go sometimes into the Sargasso Sea and not see very much. But other times, you can encounter masses [of sargassum] that do really look like great islands. Christopher Columbus described encountering these great masses of seaweeds. It's like having a garden out in the open ocean. It's why so many creatures find shelter out in the open ocean.

What are the threats currently facing the Sargasso Sea?

The greatest concern, other than the same kinds of issues that face all of us [like] climate change and the changing chemistry of the ocean through acidification, is the direct disturbances caused by shipping. You certainly upend the [seaweed] masses and all the little creatures that are there.

Storms do this too, but we're the added storm that continues to disrupt and break up these large masses.

No one's suggesting that we stop shipping through the Sargasso Sea, but the goal is to try to identify critical migration routes so we can advise ships crossing areas where whales can be encountered, or where tuna are migrating.

How were you involved in this agreement to protect the Sargasso Sea?

As a consequence of the TED Wish that I made in 2009, when I was given the TED Prize, we were given funding that made it possible for us to have a remarkable expedition to the Galápagos Islands.

One of the people on the expedition, [businessman and conservationist] David Shaw, was inspired to take this idea of working through the Bermuda government and with scientists there and elsewhere, and put together the Sargasso Sea Alliance to foster this agreement to win protection of two million square miles of it. Getting nations to agree to exercise care and to not exploit it with long-lining or stripping it [for resources].

He and a group of others on that ship got their hitch together and that's where the Sargasso Sea [Alliance] was born. I was part of the steering committee.

We now understand that more than half the oxygen that we breathe comes from the sea. It's our life-support system.

Heretofore, it was looked at as a source of goods or means of transportation, or sometimes a convenient place to conduct warfare.

[But] the most important thing we extract from the oceans is our existence. This is the moment in time, before we carve up the rest of the world to satisfy short-term interests—there is the opportunity to step back and embrace the high seas as an insurance policy if nothing else.

The agreement states that the signing countries will voluntarily take steps to conserve the Sargasso Sea. What does this mean in practice for a country like the U.S. or Bermuda?

They've agreed to promote care of the Sargasso Sea and enlist other governments to do the same. To use their power, such as it is, individually and collectively, to create this awareness of what's at stake. [The agreement] certainly can lead to binding policies. But at present, it's more a celebration of understanding that this is an area that matters.

There were a number of countries that were very interested in the concept, but there was concern that it might inhibit some of their vested interests in terms of fishing. Fishing is the biggest issue that's on the table.

Already there's significant depletion of animals in the Sargasso Sea. From turtles to whales and eels, to the most prized fish on the planet, the bluefin tuna, and other tunas as well.

What are the next steps?

What will come out of the most recent meeting in Hamilton [Bermuda's capital] is a Sargasso Sea commission. That's the next step for the process. But the steering committee, we've done our job up to this point. But I will stay engaged.

I first heard about the Sargasso Sea as a kid in Florida—I think I was 13—when reading William Beebe's book Half Mile Down. I was entranced with the idea of getting into a submersible in the Sargasso Sea. They described the most incredible creatures in the deep sea. I was hooked.

The idea that you could go down into these clear waters, down into the darkness below, and you find yourself in this magical world: It really has been responsible for provoking me to take on the ocean as my principal guiding star.

Protection for the open sea—and the Sargasso Sea in particular—protecting it right now, it doesn't cost any nation to just abstain from large-scale fishing or being smart about where you channel boats, or to be mindful of where you put the pollution.

This interview has been edited and condensed.