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MBARI researchers discover remarkable new swimming sea slug in the deep sea mbari.org
MBARI* researchers have discovered a remarkable new species of sea slug that lives in the deep sea. Bathydevius caudactylus swims through the ocean’s midnight zone with a large gelatinous hood and paddle-like tail, and lights up with brilliant bioluminescence. The team published a description of the animal, nicknamed the “mystery mollusc,” in the journal Deep-Sea Research Part I.
Standing on a windy bridge over the Des Plaines River in Joliet, Illinois, Scott Whitney shows off a diagram of what he calls the gauntlet. Pictured is a half-mile-long underwater obstacle course for fish that runs upstream toward Lake Michigan. A curtain of turbulent bubbles is followed by a bank of speakers emitting ear-splitting noise, then a wall of electrified water and finally a navigation lock designed to flush downstream any organisms that make it that far. “It’s hell for the fish,” says Whitney, chief of the project management branch for the US Army Corps of Engineers’ Rock Island District.
He’s focused on one in particular: invasive carp, which have menaced Midwest rivers for decades. Whitney’s gauntlet -- officially known as the Brandon Road Interbasin Project at the Brandon Road Lock and Dam -- aims to stop the carp from getting any closer to Lake Michigan. Scientists deem this spot the fish’s likeliest entry point into the Great Lakes and its fishing industry, which the Great Lakes Fishery Commission values at $5.1 billion annually. The Corps plans to start building the BRIP in January at a cost of $1.15 billion, with Illinois, Michigan and the federal government splitting the tab.
An invasive black carp.The barrier will be the most ambitious defense against the carp in America. Their deep hunger for plankton has wreaked havoc on ecosystems, effectively pushing out native fish throughout the Mississippi and its tributaries. In addition to screwing with the food chain, the carp are despised by fishermen. Silver carp -- one of four closely related species native to different parts of Asia -- sometimes leap into the air at the sound of an outboard motor, a stress reaction that has knocked anglers unconscious and shattered facial bones.
Already, state and federal governments have poured hundreds of millions of dollars into control measures, including electric barriers, harvesting programs and even campaigns aimed at chefs and home cooks. But none will attempt to seal off the carp’s potential passage into the Great Lakes with this level of investment. “There really is no other project, probably in the history of humankind, that has put so much time, money and effort into trying to curb the movement of an invasive species,” says Jim Garvey, a professor of zoology and director of the Center for Fisheries, Aquaculture and Aquatic Sciences at Southern Illinois University.
The US’s struggle against invasive carp started with a well-meaning blunder, as journalist Dan Egan writes in The Death and Life of the Great Lakes. In the 1970s government scientists in Arkansas were testing to see if carp imported from Asia could, as an alternative to chemicals, clean up algae from catfish farms and sewage lagoons. Eventually funding ran out, and the research stopped. But some of the experimental fish were released, finding their way into surrounding waterways. The scientists thought the fish wouldn’t breed in the wild. They were wrong.
As they’ve migrated up the Mississippi River basin, two species have had a particularly suffocating effect. Silver and bighead carp can live for decades, eating pounds of plankton every day. Studies have found silver carp make up more than 90% of the aquatic biomass in sections of the Mississippi.
In 2002, as part of a broader congressional effort to control invasive aquatic species, the Army Corps installed its first electric barrier to fend off non-native fish in the Chicago Ship and Sanitary Canal, the critical connection point between the Mississippi basin and the Great Lakes. In a section of the canal in Romeoville, Illinois, about 10 miles upriver from Brandon Road, an underwater carpet of electrodes emits an electrical field designed to deter carp that swim near it. Over the past two decades, the Corps has spent about $286 million adding similar barriers in Romeoville and tweaking their voltage levels.
Inside the chamber of the Brandon Road Lock, drained during recent construction work.How effective these have been is a topic of controversy. No carp has been documented passing through them. But a handful of carp and a lot of their DNA have been found upstream of the barriers, close to Lake Michigan. After one DNA discovery in 2009, Michigan sued the Corps and Illinois, demanding the canal be closed because of the carp’s threat to Great Lakes fisheries. Such a closure would’ve blocked the small amount of barge traffic that uses the canal to travel in and out of Lake Michigan and forced Chicago to rethink its wastewater disposal. Debate raged over what closure would cost: The Corps pegged it at $18 billion; advocacy groups put it closer to $2 billion.
The case wound its way to the Supreme Court, which eventually rejected the closure request. But the sense of emergency was real. “‘ Terminator’ carp threatens Great Lakes,” the Guardian proclaimed in 2010. Then-President Barack Obama nominated a carp czar to oversee eradication efforts.
Amid the Great Carp Alarm, Congress directed the Corps to study additional options to prevent invasive species from spreading between the Mississippi basin and the Great Lakes. In 2019 the chief of the Corps signed off on the Brandon Road project. Its deterrents are crafted to target carp at different life stages, Whitney says.
Since most of the project is underwater, the view from the bridge where Whitney is showing off the plan won’t be that different when the BRIP is complete. The changes will be below the surface: The channel is being reconstructed to eliminate fish hiding spots or food sources and to shore up the structural integrity of the 91-year-old navigation facility. The plan is to install the BRIP’s electrical barriers with superior insulation to the ones operating in Romeoville, which have been known to throw out stray voltage. The noise from the underwater speakers will sound a little like a fork caught in a lawn mower.
Biologists are optimistic that the BRIP will keep carp at bay. And, really, it’s designed to be redundant with the setup in Romeoville, which will continue to operate at a cost of about $15 million per year. Illinois also spends more than $2.5 million a year paying fishermen to pull millions of pounds of carp out of the rivers. (In 2022 the state led a campaign to persuade chefs to put carp on restaurant menus, re-branding it “copi,” short for copious, but it hasn’t caught on.) “There is no single thing that anyone can do to make it a surefire” deterrent, says Reuben Keller, a professor of environmental science at Loyola University Chicago who studies aquatic invasion ecology.
Definitions of success may vary. The goal of the BRIP is to stop carp to the greatest extent possible, but there’s no official key performance indicator. Whitney acknowledges that, over time, carp could adapt to the BRIP’s deterrents and swim past them. That’s why he considers the project an example of “adaptive management,” meaning the Corps will continue to develop and add anti-carp defenses as necessary. “It’s the best we can do today,” Whitney says, “to prevent disastrous consequences if we fail.”
Laura Bliss is an editor and writer at Bloomberg Businessweek.
This Invasive Vampire Fish Is Helping Researchers Understand the Human Nervous System in Jaw-Dropping Ways
The sea lamprey looks like it’s from another planet, but this ancient creature has a surprising amount in common with humans
A sea lamprey shows off its nightmarish mouth.
Key takeaways: Sea lampreys and research
Sea lampreys have large neurons and synapses, making them ideal for neuroscience research.
Scientists study the creatures to learn more about how we might recover from spinal cord injuries.
With a suction-cup mouth and over 100 teeth, the sea lamprey has earned the nickname "vampire fish" and comparisons to sea monsters. Sea lampreys are one of the world’s most ancient fish species, killing prey by latching their suction-cup mouth onto a fish's skin and rasping away the fish's flesh with a rough tongue to feed on blood and bodily fluids.
Sea lampreys sound like something from a horror movie, but the creatures have been crucial to almost two centuries of neuroscience research. Neuroscientists study sea lamprey spinal cells, which the animals can regenerate if their spinal cord is damaged, as a model to understand the human nervous system, spinal cord injuries and neurological disease. The evolution of human brains and nervous systems is also closely tied to these alien-like creatures.
Neurologists and zoologists began studying lampreys in the 1830s, examining their nerve cells to understand how the spinal cord works. Lamprey research took off after 1959, when biologists first described lampreys’ ability to regenerate spinal cord neurons and eventually swim after spinal damage.
Sea lampreys are ideal for neuroscientists to work with because the animals have large nerve cells and synapses, making observation easier than in other species. “The synapses are so big that you can see them, and you can record from them and access them very easily,” says Jennifer Morgan, neuroscientist at the University of Chicago’s Marine Biological Laboratory. The creatures also have a similar molecular and genetic toolkit to humans, she says, which can make it simpler to translate research from lampreys to humans and find tools that work in both species.
Lampreys thrive in different types of water, all over the globe. “[Lampreys] have been found on every continent except for Antarctica,” says Morgan, whose lab uses sea lampreys for research. “So, they’re very hearty animals and super easy to maintain.”
The sea lamprey (Petromyzon marinus) filter feeds as a larva but becomes parasitic once it reaches adulthood, latching onto fish and feeding on their blood. They can feed on trout, salmon and other large, commercially important fish, and one sea lamprey can destroy up to 40 pounds of fish per year.
Much of the supply of sea lampreys for research comes from the Great Lakes, where lampreys wreak havoc on the fishing industry. Although the species is native to the Atlantic Ocean, improvements in the late 1800s and early 1900s to canals connecting Lake Ontario and Lake Erie to the ocean enabled lampreys to bypass Niagara Falls, which had previously been a natural barrier. From there, lampreys invaded the lakes, where they have no natural predators. By the 1960s, lampreys had devastated trout fisheries in the region and a control program began to weed them out using pesticides.
Sea lampreys’ invasion of the Great Lakes has actually boosted their use in research. Over the last century, the Great Lakes Fishery Commission has directed considerable amounts of research funding toward lampreys, to study their life cycle and how to eradicate them. This put more lampreys in labs, resulting in studies on other aspects of their anatomy and evolution.
Collectors catch wild lampreys in the Great Lakes, says Morgan, and send them to the lab in coolers.
“Great Lakes fisheries harvested these lampreys, and they wanted scientists to understand them more,” says Robb Krumlauf, developmental biologist and scientific director emeritus at the Stowers Institute for Medical Research, who also researches lampreys sent from the Great Lakes. “They had a natural supply that they could give to those who are interested in the research.”
Although lampreys look like they’re from another planet, they have more in common with us than it might seem. Lampreys branched off from other vertebrates about 500 million years ago, so they have some of the oldest traits in the lineage: they’re at the base of the vertebrate branch of the evolutionary tree. Because of this, studying lampreys’ genomes can clarify important evolutionary steps in the lineage—like when vertebrates developed jaws, or arms and legs.
Sea lampreys survived multiple mass extinction events, including the asteroid 66 million years ago that wiped out roughly 80 percent of life on Earth. “It’s a chance to have a glimpse of the past. It’s sort of like a living fossil,” says Krumlauf.
Krumlauf studies how sea lamprey evolution and human evolution are related through how our faces and heads develop. The brain region that shapes facial and cranial features is similar across vertebrates, from lampreys to chickens to mice to zebrafish, even though all these animals’ heads look quite different.
“There’s a common toolkit,” says Krumlauf. “If you have building materials, and they’re all the same, you can build a garden shed or you can build a mansion––what’s different is the way the blueprint is put together.”
Studying lampreys shows how these blueprints evolved in the earliest vertebrates, says Krumlauf. His research links facial and head development in the animals to the development of craniofacial abnormalities in humans.
The evolutionary history of lampreys and other vertebrates also helps scientists like Yi-Rong Peng, ophthalmologist and neurobiologist at UCLA, illuminate the evolution of vision.
Peng’s research has found lamprey retinal cells are similar to those of other vertebrates, such as mice, chickens and zebrafish. Such a finding suggests retinal vision, like humans have, evolved early in the vertebrate lineage. Studying the overlaps between animal retinas gives a window into how vertebrates saw the world 500 million years ago. And understanding how the retina first formed in humans can help Peng’s research team study retinal cell degeneration that leads to blindness.
Morgan’s lab studies how sea lampreys regenerate spinal cords, and its work could lead to advances that help humans recover from spinal damage. When researchers cut a sea lamprey’s spinal cord, it becomes paralyzed but can regenerate nerve connections. The process does not have to be perfect to work, adds Purdue University science historian Kathryn Maxson Jones. Lampreys’ original neuron connections don’t reform in the same way, but cells grow in flexible ways to compensate for damage––biology can take different routes to achieve the goal of a spinal cord that works again. And the large size of lampreys’ cells and synapses enable the research team to closely examine the whole process.
A microscopic view of a sea lamprey’s reconnected spinal cord shows how it healed after being cut.
Sea lampreys are also crucial to Morgan’s research on Parkinson’s disease. A specific protein’s accumulation in the brain is linked to the progression of the disease, so injecting that protein into lamprey synapses allows the researchers to observe how it affects the nervous system.
This gives insight into how the disease progresses in the human nervous system and how exactly neurons can recover. Scientists observe how damaged lamprey neurons regenerate and how many synaptic connections are restored, guiding how to target treatment in human brains.
Morgan’s research team hopes to move from understanding nervous system damage in lampreys and humans to how to fix it.
When you cut your finger and the area becomes numb, that’s because of damage to the nerve endings in the finger, which is part of your peripheral nervous system, explains Morgan. But you do eventually get feeling back, because humans can regenerate cells in the peripheral nervous system––just not in our central nervous system.
But lampreys can. “When lampreys regenerate the spinal cord and recover function, they are using a lot of the same changes in gene expression that occur during regeneration of the peripheral nervous system in mammals,” says Morgan.
“Why we can’t do that in our spinal cord is a big question. But I think learning from the adaptations of these animals, that can do these really neat feats of nature like regeneration, will tell you something about the recipe that needs to happen, the conditions that need to be met,” adds Morgan.
And the parallels between lampreys’ brain features and ours make crucial research possible when studying human brains isn’t an option. “It often points us in the direction of things we would’ve never looked at in humans,” says Krumlauf.
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