The Panama Canal Has an Unusual Ecosystem, Flowing From Fresh Water to Salt Water and Serving as a Home to Crocodiles, Manatees and Sea Squirts. New Intruders Pose a Growing Threat to the Waterway

The Panama Canal Has an Unusual Ecosystem, Flowing From Fresh Water to Salt Water and Serving as a Home to Crocodiles, Manatees and Sea Squirts. New Intruders Pose a Growing Threat to the Waterway

The species that occupy this artificial channel are transforming, thanks to a shifting environment and invading marine creatures. The Smithsonian Tropical Research Institute is tracking what happens next

Georgia Michelman | Editorial Intern

November 9, 2026 7:00 a.m.

Every year, about 15,000 ships pass through the Panama Canal. But this human-constructed waterway—which connects the Atlantic and Pacific Oceans—is more than an economic hub. Beneath the steady boat traffic, the canal is bursting with life. A vast array of creatures dwell there, from native freshwater species, like tilapias and manatees, to marine species, like crabs and sea squirts, that have stowed away on ships.

Panama is “prime real estate” for studying ocean animals, says marine ecologist Mark Torchin, the chief scientist at the Smithsonian Tropical Research Institute (STRI), which is based in the Central American country. Between two oceans and the mostly freshwater canal, STRI scientists have plenty to work with.

Before taking on his current Zoom-heavy role as chief scientist, Torchin spent nearly two decades as a staff scientist at STRI. Throughout this time, the salinity of the canal has been rising, making his lab’s focus on marine invasions even more important.

Recently, scientists from Torchin’s lab were featured in an upcoming episode of the Smithsonian Channel documentary series “How Did They Fix That?” Host Mike Davidson shadowed several STRI scientists researching changes to the canal’s unusual ecosystem. Torchin didn’t make an on-camera appearance, but he’s glad to have seen his team’s important work highlighted.

How Did They Fix That? 'Panama Canal' Sneak Peek 1 | Smithsonian Channel

Ahead of the program’s release this Monday, November 9, Torchin spoke to Smithsonian magazine about the species occupying the Panama Canal and STRI’s work tracking and combating threats to the artificial waterway.

This interview has been edited for length and clarity.

What’s the Panama Canal’s ecosystem like? Is it different from other nearby bodies of water?

It’s a completely unique ecosystem. It’s a human-created system, right? Basically, the damming of the Chagres River formed Lake Gatun and enabled the Panama Canal to be created. Previously, that whole environment where Gatun Lake now sits was land, and it was flooded. It’s a man-made reservoir lake.

Some of the freshwater species that were associated with the rivers moved into the lake. So there are native species in the lake, but it’s been augmented by introductions—both intentional and accidental—of other species that move in there. If you take a boat trip through the Panama Canal and Gatun Lake, it’ll look like a freshwater environment, but the salinity gradient is fairly steep because once you hit the locks, it goes from predominantly freshwater down to completely seawater.

What’s happening in Lake Gatun is its very low salinity is creeping up a little bit because of the seawater intrusion. Depending on where you go, you can get pockets of higher salinity, and often that’s where you find some more marine-tolerating species. They’re generally species that can go into estuaries in that interface of brackish water and marine water. But now you’re finding them in the lake as well.

Did you know? Canal water

The fresh water that streams into the Panama Canal serves more than just its strange assortment of creatures. These reservoirs also provide drinking water for around half of Panama’s population.

Why is there more seawater intruding in?

We don’t exactly know what’s influencing that. More locks, bigger locks, bigger ships moving in. The water-saving basins on the new locks that conserve water also are hypothesized to retain seawater and movement into the canal. So those are all sorts of hypotheses as to why that might be happening, but it’s a little hard to test.

People don’t normally think of wildlife when they think of the Panama Canal. What species live in the canal?

That’s changed over time. Shipping and human activities move critters through the canal, and so you get exchange across the Atlantic and Pacific that way. The other is critters that move on their own. These are mostly fishes, but not exclusively. There are crabs that can do it, too, and other species. But fishes are one that we’ve been most focused on over the past decade.

So, yeah, marine crabs, marine fishes, bivalves. You go from a more marine sort of habitat on the outside, on the ends of the canals, into a more freshwater sort of situation, and throughout that continuum, you see both marine introduced species, species that can tolerate more freshwater, and then exclusively freshwater introduced species as well.

When you talk about marine species moving into the canal via ships, can you help people visualize how that happens? Are they getting trapped? Are they latching on?

Kind of all of the above. Cargo ships utilize ballast water to retain stability at sea, depending on how much of a load they carry. Ballast water is water that is usually brought in through pumping mechanisms in big chambers called sea chests. If you pump in a bunch of ballast water from an environment, that can include larvae from marine species. It can include planktonic marine species. It can include even small fishes.

So the intent is not to suck species in there, but that’s a consequence. The other is hull fouling, and so that’s now being recognized as a big contributor to introducing marine species, probably on par [with], if not more, than ballast water. So these are barnacles, mussels, sea squirts that stick to the hulls of ships.

So it’s smaller species or larvae that are getting sucked in, and the species stuck to the hull.

Usually. Although adult fishes have also been found. Have you ever been on a dock in a marina and looked off the side? It’s not just a flush surface. It’s a bunch of critters that basically grow on that, and the more stuff growing, the more additional critters you have hanging on.

So even though a lot of those species are sessile invertebrates, you’ll get fishes intertwined with that. Little octopods, sea stars, crabs—there’s a whole community that can live on there. Move that around to a new location, and those species can then establish.

Have canal species evolved in unique ways?

I think it’s been about 110 years since it’s been open. So that’s a pretty narrow window for evolution and understanding evolutionary changes. The Atlantic and Pacific Oceans used to be connected by the Central American Seaway millions of years ago. And—depending on who you talk to—about 3.5 million years ago, the final separation between the Atlantic and Pacific occurred. Marine species that used to be across that whole region were separated and speciated, and so that’s really a test bed for and a natural experiment for evolution, and how those species have changed.

There are certain species of fish, species of crabs that are congeneric sister species. So they’re very similar. Over the past 3.5 million years, they have evolved in different environments, but they’re fairly closely related. The question is: If they come together again, what’ll happen? So that’s really an interesting evolutionary question. As far as what’s happening with the marine species moving in, there’s another potential interesting question: How are they adapting to this mostly freshwater situation? And that’s another thing that we’re trying to understand now.

What are some scientific discoveries that you’ve made during your time at STRI?

The opportunity to document invasions in real time. We’ve had a series of folks in our lab working on fishes in the Panama Canal, starting from before the Panama Canal expansion [in 2016] to the present day.

What we’ve seen is a shift, in the places that we’re looking, from a predominantly freshwater fish community in the canal to a predominantly marine community. So the whole system has shifted over the course of about 15 plus years, and we’re trying to understand kind of why that is and what the implications are.

On the marine side, the conventional wisdom is that tropical regions are generally less invaded, and [there’s] few reports of invasive species in these tropical regions. We’re finding quite a few introduced species, but in most cases, they’re not super abundant. So something’s keeping them in check. That’s really what shaped the other component of our research: understanding how this native biodiversity is limiting the distribution and abundance of species.

How Did They Fix That? 'Panama Canal' Sneak Peek 2 | Smithsonian Channel

If you have boats coming in and out all the time, does that threaten species?

I think yes and no. There’s probably some adverse effects of shipping, but you’re also moving species around. So there are these introduction events. A big impact of shipping has been on some of the bigger critters, so megafauna like whales. Hector Guzman, a marine biologist at STRI, a colleague of mine, has been working on looking at humpback whale migrations, particularly sort of around the Bay of Panama and near the entrance to the Panama Canal.

He tagged a bunch of whales, trying to understand where they’re going, and based on that, he was able to work with the Panama Canal Authority as well as the government of Panama to change some of those shipping lanes going out of the Panama Canal in the Pacific to avoid collisions with whales. So that’s an example of where science influences policy, and you’re sort of saving the lives of charismatic species.

What kind of large creatures actually live in the canal?

The biggest critter is probably manatee. Atlantic populations of manatees were put in the canal, presumably to eat some of the vegetation to control that. Crocodiles are common in the canal, [and] caiman. Probably the biggest fish is the Atlantic tarpon, which can get a couple meters in length.

What do other ongoing conservation efforts look like?

Two programs were featured in the Smithsonian Channel program. One was the marine fish invasions. The other was the Agua Salud program. Agua Salud is a large-scale experiment that’s been running for a couple decades, looking at how land use practices influence water flow, water quality, in addition to several other ecosystem services.

What are some examples of land activities impacting the water?

The Panama Canal relies on rivers that go into the canal and several streams that feed into those rivers and the associated watersheds. A lot of stuff happens on land in those areas. There’s primary forest, which is generally untouched, that’s becoming less and less these days. There’s secondary forest that’s been cut and growing back. There’s cattle grazing, so silvopastoral land, compacted land. There are tea plantations.

What the Agua Salud project tries to do is intentionally using those different practices to test how they influence those factors that we talked about. From a conservation perspective, looking at planting native trees and native tree restoration benefits is one aspect. In terms of the aquatic realm, humans are relying on that for their livelihood. Artisanal fisheries, sport fisheries basically rely on both native and introduced species in that area.

Thinking about how that’s changing as more marine species move in is another area for consideration for conservation. There are social scientists working with some of the fishers to try to figure that out. Carolina Chong-Montenegro is one of them that’s featured on that episode as well.

What are some of the water issues in the canal?

First and foremost is water flow. So from January through April into May, Panama has a dry season. That’s exacerbated by the El Niño that’s coming. So water levels get really low in the lake, and the Panama Canal Authority has to reduce or restrict vessel movement through there.

That influences everything—economics—so water flow is a main issue. The other is: You don’t want murky water flowing into the canal for several reasons, including predominantly that it’s one primary source of Panama’s drinking water. So forests both protect and regulate that dry-season flow as well as the water purity or the clarity of the water going in.

How do severe droughts impact species?

Severe drought on land certainly influences the trees and how they survive and how they flower and bloom. Severe drought in the canal reduces the water levels. We’re predicted—with this El Niño—to go into another drought period. So what you would see on land is basically drought-tolerant [plant] species would do better. For critters in the canal, some of those species that rely on higher salinity might do better.

What kinds of those salinity-reliant marine species are you seeing?

One thing we’re seeing is the Maryland blue crab, which the native range basically extends into the tropics, Callinectes sapidus. Now, for ten years, we have been seeing it move into the Panama Canal, and generally, that’s associated with areas that tend to be more saline. But we need more data to really accurately say that. Snappers are moving into the canal. Recently, we put out a report of a bull shark found in the canal. Some interesting finds in there.

Can you talk about more current challenges that may threaten species in the Panama Canal?

Human encroachment into those areas is probably a big one. Certainly, the climate is changing, with this impending El Niño, which is a natural phenomenon. But on top of that, a warming Earth has implications for potentially bigger changes. I think we don’t understand a lot of that, so more research in that context would be useful as well.

Invasions across the Panama Canal is the other thing. The real question is: If a Pacific species moves into the Panama Canal, what happens if it moves out into the opposing ocean? So that’s really an interoceanic invasion, and that’s one area to consider what that would mean, and how that would shape the environment if that became more frequent.

From our perspective, the Panama Canal is just a great natural experiment to test ideas around marine introduced species. We’re kind of witnessing invasions in real time. So the question is: What influences the likelihood of that happening, and how do we sort of mitigate that or reduce that probability?

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