When neighborhoods start to go downhill, people move away. And today, that’s happening in marine neighborhoods. As the oceans get warmer—a result of our changing climate—fish and other critters are moving out of their neighborhoods and into cooler waters. That includes the tiniest organisms, known as plankton. And a recent study says the trend could accelerate in the decades ahead.

Researchers at the University of Texas and elsewhere pored through a database of half a million microscopic plankton fossils—in particular, a group known as Foraminifera. Many of the fossils are millions of years old. And they reveal how the Foraminifera have moved around in response to climate changes.

Eight million years ago, global temperatures were about the same as they are now. But our planet cooled off after that. As it did, the plankton moved toward the equator, and set up in tropical neighborhoods. As temperatures have climbed in recent decades, though, they’ve reversed course—they’re moving away from the equator and toward the poles.

That could have a big impact on the entire tropical ecosystem. The plankton form the base of the marine food chain, so as they move to cooler waters, larger organisms will have to follow or die off. That means tuna, marlin, squid, and other species will become less common in their current tropical homes. And that could decimate commercial fishing operations, ecotourism, and other businesses—hurting tropical neighborhoods around the world.