By John DiConsiglio
For 500 million years, the nautilus has roamed the deep tropical waters of the Indio-Pacific Ocean region. With chocolate brown stripes adorning its smooth, white shell, the unassuming mollusk has seen dinosaurs come and go. It has survived natural disasters from asteroids colliding with Earth to devasting quakes that reshape terrain. The nautilus has adapted to shifts in the Earth’s ecosystem and changes to the chemical makeup of the ocean.
So why are these so-called living fossils dying in zoos and aquariums around the world?
That’s the mystery consuming Mehdi Moini, associate professor of forensic sciences in the Columbian College of Arts and Sciences, and a team of multidisciplinary scientists gathered by the Smithsonian Institute. Studying captive mollusks from the National Zoo collection, Dr. Moini is part of a detective squad of chemists, pathologists and museum curators who are looking for answers to why the nautiluses are dying at such fast rates in captivity.
In their natural ocean habitat, the nautilus can live 15 years or more. But overfishing and the booming trade on their decorative shells have decimated the wild-nautilus population. Aquariums and zoos have become vital species-saving refuges and home to behavioral and developmental studies.
In captivity, the nautilus’ life span is only two to three years. And scientists are not sure why.
With the nautilus now on “the knife-edge” of extinction, as Dr. Moini puts it, preserving the life cycle of the family is crucial because the nautilus provides scientists with one of the earth’s oldest living creatures that has remained basically the same for a half-billion years.
“This is an animal that has remained virtually unchanged for millions of years. Studying the nautilus is like looking through a window into the planet’s evolution,” Dr. Moini said. “It’s a scientific goldmine.”
Dr. Moini and the team of researchers have uncovered a significant clue, they believe, one that was published with their research on the nautilus in a recent edition of the journal Zoo Biology.
Once the nautilus is removed from its natural environment, a thick, roughhewed black substance develops on a portion of its smooth white shell. Examining samples from three nautiluses, Dr. Moini's team compared proteomics from the healthy portion of the shell with that of the diseased portion that developed in captivity.
In search of a solution, Dr. Moini and his team used an array of scientific equipment—from isotope ratio mass spectrometry (IRMS) to micro X-ray fluorescence (XRF) to the Forensic Department’s state-of-the-art proteomics instrument, the Thermo Orbitrap.
When the scientists ran the samples from the three nautiluses through both the IRMS and the XRF, they found a severely tilted protein imbalance. The healthy white portions of the shells were normal. But the inky black areas were heavy with hemocyanin, a protein that leads to excess amounts of copper, which can be harmful to shell formation. In addition, the discolored sections had lower levels of “healthy” proteins.
“When I saw this, my eyes lit up. These levels shouldn’t be present,” Dr. Moini said. “Proteins are responsible for building the shell, so when we see that much copper, that’s alarming.”
The black shell streaks aren’t killing the nautilus, Dr. Moini believes. Instead, he said, they act as a “biomarker”—a sign that something in the animal’s physiology has gone awry.
“It’s like when a human takes his temperature,” he said. “It’s the nautilus’s way of telling us, ‘I'm not feeling good.’”
The team tried to follow the black-substance trail to the nautilus killer. But all the usual suspects had alibis. There were no traces of dangerous pathogens, like bacteria or viruses, in the samples. Factors like variations in the captive animal’s diet or tank-water chemistry also quickly were ruled out.
But that left a tantalizing possibility: stress. When a nautilus is removed from the wild and placed in captivity, it experiences environmental stress—from changes in pressure to shifts in temperature to new light patterns and oxygen levels. “Think about the stress they are subjected to: there’s the physical and chemical stress, the capture is stress, their new living environment is stress,” Dr. Moini said.
He believes these stresses trigger a physiological change that reinforces the nautilus shell—hence the black deposits. Those same stress factors may be affecting the animals in a more lethal manner. “I'm sure there is some correspondent internally,” he noted.
More research is needed before the source of the what’s killing the nautiluses can be identified. But time could be running out. Only 25 aquariums and zoos have been able to maintain nautilus collections, and only four have successfully bred them. In the wild, overfishing has slashed nautilus numbers by as much as 80 percent in once-rich areas like Australia’s Great Barrier Reef and the Philippines’ Bohol Strait. With virtually no international sanctions limiting the capture and trade of the nautilus, shells can sell for several hundred dollars. The United States alone imports 100,000 nautilus shells each year.
The loss of the nautilus could hinder scientific studies in everything from evolutionary trends to climate change effects on the oceans to human bone formation. “This is an animal with a remarkable capacity for survival,” Dr. Moini said. For the sake of science, Dr. Moini and his team are fighting to keep it that way.