The presence of invasive swamp eels in the Everglades is causing concern among scientists who study the region’s delicate ecosystem. First identified in South Florida in the early 2000s, these fish are believed to have been introduced through live food markets from Southeast Asia. Their rapid spread has led to significant changes in the marshes, particularly in Taylor Slough.
Nathan Dorn, an aquatic ecologist and associate professor of biological sciences at Florida International University (FIU), has observed a dramatic decline in populations of crayfish and small fish over nearly two decades of research. Dorn noted, “These were numbers and densities of particularly the crayfish and a couple of fish that we’d never seen before. They were so low, they were basically absent from the system.”
Electrofishing surveys confirmed that swamp eels have become a major predator within the large fish community. In a recent study with FIU postdoctoral associate Matthew Pintar, Dorn found that up to 80% of the prey base for seasonally nesting wading birds has disappeared from Taylor Slough.
Historically, wading birds such as white ibis, great egret, little blue heron, and tricolored heron have relied on these wetlands to feed their chicks primarily with fish. Dorn explained, “If we’ve rerouted water in Florida to recapture even some of the functions of historical Everglades, we expect to see relatively high numbers of nesting birds on a semi-regular basis in Everglades National Park. But the birds are fundamentally limited in their nesting efforts by food availability.”
The loss of primary food sources for wading birds has altered feeding relationships throughout the marsh and reduced biodiversity. Scientists describe this as an ecosystem collapse—not a total breakdown but a significant shift in how species interact.
“It’s not that the Everglades is a completely collapsed ecosystem,” Dorn said. “It’s just a rearranged ecosystem in terms of its food web that is taking on a whole new characteristic just by a change in a top predator introduced unthinkingly.”
Swamp eels’ ability to survive drought conditions by burrowing into mud and breathing air gives them an advantage over native species. When water returns after flooding, they are ready to prey on young crayfish and fish.
“That’s not something that we think is a normal phenomenon,” said Dorn. “It’s a really novel predator with some novel traits and it’s a new sort of loss factor for our fish in the system.”
Dorn suggested that while some native animals might adapt to this new threat, it remains uncertain whether balance can be restored: “They don’t behave like any of our native fish, yet they control everything else. Now you’re depending on the rest of the system to adapt to that animal, but it’s probably not going to be the system or the community that we were anticipating we’d get.”
He emphasized caution regarding invasive species: “You almost have to take an invasive or introduced species as guilty until proven innocent, rather than the other way around, because you’re not going to get them out without an incredible amount of effort.”
Dorn concluded that prevention should be prioritized. If adaptation does not occur naturally within the ecosystem, restoration plans may need adjustment to reflect current realities rather than past expectations.
