Coastal communities are in trouble.

You’ve probably heard about  beaches shrinking and towns flooding more often as sea levels  rise due to climate change. So you might expect that to  be catastrophic for tiny, low-lying islands in the middle of the ocean.

And yeah, for decades, researchers  have expected rising seas to swallow entire islands,  especially those near coral reefs. But that’s not what’s happening. Instead, most of these islands  have stayed the same size, and some of them have gotten bigger.

So let’s talk about the weird reasons  why, and how we can keep it that way. [♪ INTRO] First, we need to talk about atolls. No, not the fees you pay to drive on the highway. An atoll is a ring-shaped coral reef structure with islands peeking above the surface.

Atolls can have up to several hundred islands, most of which are smaller  than 10 square kilometers and only a few thousand years old. When you step foot onto a stunning  white-sand beach on one of these islands, you are literally standing on the  skeletal remains of sea creatures. Coral, molluscs, and other  organisms produce calcium carbonate, which becomes the sediment that forms the islands.

Globally, the average sea level has risen  by more than 20 centimeters since 1880. And sea levels are rising near these  atolls even faster than they are elsewhere, and they could rise by another  60 to 70 centimeters by 2100. That’s a pretty big deal given  that most islands in atolls are only 1 to 5 meters above the water.

In 2010, researchers published the first  quantitative analysis of how atoll islands have changed in shape in recent decades  and found something really weird. Most of the islands were staying the  same size, and some were growing. Imagine pouring too much  water on your potted plants and then seeing the soil rise up  somehow instead of getting submerged.

That’s basically what the data showed. And that first study wasn’t a fluke. In  2018, an analysis of 709 islands across 30 atolls in the Pacific and Indian  Oceans found that nearly three-quarters of the islands were stable in size, 15%  got bigger, and only 11% got smaller.

None of the islands larger than a  tenth of a square kilometer shrunk. But just because an island stays the same size does not mean the shoreline isn’t changing. For example, one island in  the Maldives is gradually moving south and rotating as the  northeastern shoreline erodes and more sand arrives on the  northwestern and southern shorelines.

And this has to do with what  these islands really are. Remember, atoll islands are not solid  rock, they are piles of dead coral stuff. And the dead coral that forms  them can be moved around.

In other words, waves shape  atolls, and atolls shape waves. Let’s say a big wave heading east  hits the western edge of an atoll. Like a conveyor belt, the wave will  pick up sediment from the coral factory below the island’s surface,  and then dump some of it on the western shores of  the first islands it hits.

Then the wave will continue through the gaps between the islands, weaker, but still powerful. And when the wave hits islands  farther east in the atoll, it will deliver sediment to  their western shores too. The direction and strength of the waves depends on the direction and strength of the  wind, which can vary throughout the year.

In the Maldives, for instance, the winds  blow from the west for about 8 months, and then from the east for about another 4 months. And the waves are up to 5 times stronger  when the winds blow from the west. These patterns can cause seasonal variations  in how much sediment is deposited, and where, which ultimately  plays a key part in determining where the islands formed in the first place.

But seasonal wave patterns  aren’t the only architect directing the island-building process. Storms like cyclones can erode  shorelines by washing sand out to sea, or build them up by breaking  off coral rubble from the reefs. And human infrastructure comes into play, too.

Just look at what happened  in 2021 in the Maldives. On the island of Himandhoo,  a new harbor prevented waves from shipping sand to a nearby beach. As the beach eroded, they found a gnarly surprise: Dead bodies from a forgotten burial ground.

Not a great vibe for the resident  who wanted to build a hotel there. Between all these factors, there’s no  clear trend in which parts of atoll islands are shrinking and which parts are growing. But the deposits of sediment  are keeping them above water.

Even without climate change, these  islands are always shapeshifting— a recent study suggested that  over the past thousand-plus years, one island’s shoreline has  meandered as much as 200 meters. Now, this is not to say that it’s all  sunshine and rainbows for these islands. For one thing, climate change is  causing more intense tropical cyclones.

And sea-level rise threatens the supply  of drinkable groundwater in atolls. A lot about the future of atolls is  uncertain, but the bottom line is that they do have a future (most atoll islands aren’t  going to vanish beneath the waves). Because the coral factory continues manufacturing new sediment and shipping it to the shores.

They add an average of 0.1 cubic meters  of sand per meter of coastline every year, which may not sound like a lot, but it is. So we need to make sure that  humans support this natural process rather than getting in the way. By protecting and restoring reef ecosystems, we can ensure that they  produce enough new sediment.

Plus, when the sediment arrives, we need  vegetation to keep it from eroding away. Diverse native plants are great  at holding onto soil and sand. Much better than a monoculture of coconut palms.

And when we build infrastructure,  we need to design it in a way that maintains the conveyor  belt of sediment from sea to shore. All of that will protect these  atolls for years to come. And avoid surprise dead bodies  washing out, which is also a bonus. [♪ OUTRO]