Early last year, a team of researchers dropped three alligator carcasses over a mile deep into the Gulf of Mexico. The goal was to see what would turn up to eat them.
When dead whales and big logs fall to the bottom of the gulf, “there’s a whole host of species found on them that aren’t found anywhere else in the ocean,” said Craig McClain, a deep-sea biologist in Louisiana.
The crocodile lineage dates to the Mesozoic Era, when the seas teemed with enormous marine reptiles. When those reptiles died, fossils show that marine scavengers happily devoured them.
So Dr. McClain and his team hypothesized that unique ocean creatures might be waiting for crocodyliform meals.
“We wondered if we did alligator falls, if we’d recover species that haven’t been previously known to science — relics and refugees from a time when marine reptiles dominated the ocean,” he said. “Are we going to be able to uncover an ancient fauna?”
The research, published last month in PLOS ONE, didn’t just turn up a new species that thrives on alligator bones, but also revealed surprises about the food web deep beneath the Gulf of Mexico, including how carbon from Earth’s surface gets recycled in the oceans.
Usually, Dr. McClain’s lab studies how deep-sea creatures feed on trees swept into the Mississippi Delta. But they began wondering what happened to alligators.
“There were three swimming behind my house in the harbor,” Dr. McClain said. “That got my lab thinking about alligators in general as potential food falls.”
Alligators are found in coastal habitats from Texas to South Carolina, and occasionally venture into saltwater. When they die, some must sink into the deep ocean.
Because alligators are protected in Louisiana, Dr. McClain’s team worked with state officials to acquire three euthanized alligators. They selected three sites around the undersea Mississippi Canyon, and lowered each carcass from the ship on a basket, or “benthic elevator.”
The team left the alligators weighted down in the abyssal mud. When they sent a remotely operated vehicle back a day later to check one of the carcasses, they got a shock.
Dr. McClain and his colleagues had guessed that the alligators’ tough hides would make it difficult — perhaps impossible — for undersea scavengers to devour them. But the carcass was swarming with giant isopods, a football-sized species of scavenging crustacean, which had gotten around the alligator’s armor by chewing through softer spots under the armpit.
That wasn’t the only surprise. Eight days after being deposited, another alligator’s carcass was completely missing. Dr. McClain’s team initially thought they’d returned to the wrong site, until they found drag marks. The carcass’s 45-pound weight was 30 feet away, the rope severed.
“It was completely dumbfounding to us,” Dr. McClain said, adding that the alligator must have been carried off by a sixgill or Greenland shark.
“Those are the only two sharks that reach substantial enough lengths and live deep enough in the Gulf of Mexico,” he said.
The last alligator was swarming with scavengers as well. Fifty-one days after its placement, it had been picked completely clean. The bones were covered in a species of Osedax “zombie worms.”
Other Osedax bore into the bones of fallen whales, but these worms are the first of their kind known in the Gulf of Mexico, Dr. McClain said, and represent a species new to science.
Additional research could prove whether these zombie worms are a Mesozoic-era holdover that specializes in eating reptiles that die in the ocean. For now, the study potentially reveals something about alligators’ role in feeding other marine life.
The ocean bottom gets no sunlight, preventing the photosynthesis that sustains most ecosystems. So animals living in undersea deserts depend on carbon from decaying organisms from above.
“What we find really interesting is that alligators can be a food source,” Dr. McClain said, “and a food source that’s quickly accessed and can enter into the deep-sea food web a number of different ways. Isopods. Worms. Sharks.”
If an alligator falls in the deep ocean, in other words, it does make a sound. A dinner bell.