This Invasive Species Awareness Week, Learn How Museum Researchers Track the Rogue Wildlife Infiltrating American Ecosystems

With its candy cane stripes and oversized fins, the red lionfish looks almost Seussian. But this odd-looking fish belongs to a more sinister story. With a ravenous appetite and razor-sharp spines laced with venom that can cause excruciating pain, lionfish have wreaked havoc throughout the Caribbean.

In 1985, a handful of red lionfish were released (likely by aquarium owners who no longer wanted their fish) into Florida’s warm Atlantic waters, far from their native coral reef habitat in the Indian and Pacific Oceans. Here, they found plenty of small fish to feast on — and none of the predators, parasites, and diseases that inhibited them back home.

It was the perfect storm, says Carole Baldwin, the curator of New World shorefishes at the National Museum of Natural History. “They’re eating machines, they’re reproducing machines, but nobody’s eating them,” she said. Before long, the lionfish population exploded, terrorizing smaller creatures from the Carolinas to Curacao. Now, the fearsome fish — only about a foot long on average — dominate reefs throughout the Caribbean, decimating native fish and imperiling biodiversity wherever they go.

Lionfish are part of an alarming threat to biodiversity. Humans are constantly moving species outside of their native ranges. Sometimes it is by accident, other times it is intentional. When faced with unfamiliar habitats and new predators, most nonnative animals quickly wink out. A rare few are able to establish populations. But an even smaller subset of species is able to thrive in their new environment. They reproduce almost uncontrollably and overwhelm unsuspecting native wildlife. These are the species that scientists refer to as invasive. 

Multicolored Menaces

Lionfish are among the most successful invasive species. They likely managed to get a foothold thanks to their unusual versatility: Unlike most marine fishes, they can withstand a wide range of temperatures, depths, pressures, and salinities. “Lionfish are the hardiest species I’ve come across,” Baldwin said.

Baldwin and other researchers at the museum have tracked the lionfish throughout its expansion by collecting specimens that are now housed in the National Fish Collection. However, she is worried about its impact on uncommon and poorly studied species. She poses a sobering question: “Are they gobbling up biodiversity before we even know it exists?”

Baldwin hopes that local predators like sharks and grouper will someday adapt to feast on their spiny new quarry. In the meantime, there’s only one solution that can hinder the ever-hungry lionfish: we need to eat them. Once the venomous spines are removed, the flesh, which tastes like mahi-mahi, can be prepared like any other fish. “It’s my favorite sashimi,” Baldwin said. 

Right now, it is impractical to catch enough lionfish to sustain an industry — or control the population. But someday, humans and native marine predators might make lionfish a dietary staple. 

Overwhelming mussels

Around the same time lionfish first appeared in Caribbean waters, a fingernail-sized aquatic invertebrate hitched a ride from the Caspian Sea to Lake Erie in a container ship’s ballast water. Today, that species is the most pervasive pest in America’s Great Lakes.

The zebra mussel is a very different kind of invasive species than the lionfish, sharing none of the fish’s flamboyance, predatory aggression, or venomous defenses. Instead, the striped bivalve merely sits unobtrusively on submerged surfaces in freshwater ecosystems, filtering nutrients and plankton from the water as they float by. How could this seemingly passive creature disrupt an entire region’s ecosystem — and cause up to $500 million in economic losses every year?

The primary issue is its tendency to form huge colonies. Zebra mussels do not need much space to operate: as long as water flows between their shells, they can continue to thrive regardless of their surroundings. This allows them to cluster in ever-expanding clumps, covering every available surface before clamping onto one another. In some areas of the Great Lakes, these astonishing concentrations can reach up to 65,000 mussels per square foot.

While each individual organism may not make a huge impact, it’s this density that makes zebra mussels so dangerous, says John Pfeiffer, a research zoologist and curator of bivalves at the museum. “With all these animals doing all this filter feeding, they essentially sanitize the water by pulling out all of the nutrients and microorganisms that sustain a lake,” he said.

The impacts are far-reaching. The young fish that typically rely on the same microorganisms that the zebra mussels filter often starve, which then affects larger predators who prey on the fish. Meanwhile, native mussels — some of the most endangered and overlooked organisms on the continent — are left without any food for themselves (if the invaders have not already grown directly on top of their shells). The mussels have even contributed to a rise in botulism cases in the Great Lakes thanks to a complex interaction involving increased water clarity and an invasive goby.

In addition to causing environmental devastation, zebra mussels are also a nightmare for businesses operating along the shores of the Great Lakes. The bivalves frequently latch onto water intake pipes and screens, forming huge colonies that cost companies millions. They can also affect commercial boaters and fishermen by damaging docks and clinging to boats.

Pfeiffer says that while zebra mussels have been very difficult to eradicate, it is still possible to control their further spread into inland lakes and rivers by encouraging boaters to thoroughly clean and empty their boats when moving between water bodies. In the meantime, he argues that it’s more important than ever for natural history collections to study both native and invasive species. “Natural history museums have the voucher specimens that can be used to authenticate and track the spread of biodiversity across time and space,” he said. “We have the receipts of biodiversity.”

Giant Hornets

Sometimes, scientists have had better luck curtailing new invaders. Take the northern giant hornet, a monstrous insect popularly referred to as “murder hornets.” When the Asian species was first spotted in Washington state in 2019, researchers quickly mobilized. The hornet specimens were sent to United States Department of Agriculture research entomologist Matthew Buffington, who works in the museum’s National Insect collection. Buffington used museum specimens to accurately identify the invaders.

Northern giant hornets posed a threat to native pollinators and agriculture. But thanks to an intensive intervention plan in 2020, the introduced insects never became entrenched in North American ecosystems. Scientists captured hundreds of hornets and even snuffed out a nest, which later went on display at the Natural History Museum. In 2024, the hornet was declared eradicated from the United States. It’s an important lesson on the necessity of taking swift and direct action to protect our native species.

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Benjamin Hack | READ MORE

Benjamin Hack is Science Writing Intern at the Smithsonian National Museum of Natural History. He covers anything and everything related to the natural world for Smithsonian Voices, the museum’s blog. Ever fascinated by ecology, Ben studied and conducted research in biology as an undergraduate at Cornell before transitioning into science communication. His work, which has appeared in magazines such as Audubon and Living Bird, highlights both the joy of nature and the dire challenges facing the world’s biodiversity. In his spare time, Ben can often be found outside birdwatching.