In winter 2010, Adrian Glover, a marine biologist from the Natural History Museum in London, got a call from a colleague with some good news. While piloting a remotely operated vehicle to study a hydrothermal vent 4,700 feet beneath the surface of the Antarctic’s Scotia Sea, his friend had stumbled across something unexpected: the skeleton of an Antarctic minke whale.
Rather than being a scene of death, the carcass was an oasis of life in the dark and inhospitable remote sea. Snails, worms, mollusks and white mats of bacteria were feasting on what remained of the massive mammal. Glover asked his friend to bring home a piece of this treasure.
While inspecting the bones in his lab, he discovered nine new species of worms and bacteria. These rare, relatively unexplored, deep-sea ecosystems — lively communities that spring up around dead cetaceans that sink to the seafloor — are called whale falls, or organic falls.
In all, only about two dozen have been found since researchers, led by Glover’s postdoc adviser Craig Smith, chanced upon the first discovery off the California coast in 1987. The 2010 Scotia Sea find was the first in the Southern Hemisphere.
Glover, now at the forefront of this postmortem science, is an expert on some of the worms that move into whale falls. These species and their whale-carcass cohort are helping marine biologists and paleontologists determine exactly how long large, dead marine animals have been hosting these rich communities of decomposers, and whether or not the whale falls of today look eerily like the organic falls of a time when prehistoric reptiles ruled the seas.
Watching a Whale Fall
Once a carcass sinks, it becomes home to scavengers. Species such as sharks and hagfish consume the whale’s easily accessible soft parts. When the bulk of muscle, blubber and viscera are gone, organisms called enrichment opportunists, including snails, worms and bacteria, settle in, on and around the whale. An important part of this stage are Osedax, bone-eating specialists fondly known as “snotworms” for the mucus they make.
Described for the first time in 2002, these bristly marine worms, or polychaetes, tap into bone and then rely on bacteria to help them break down fats and proteins in their new skeletal homes. But how snotworms populate whale falls in the first place remains a mystery.
Glover believes the unusual worms somehow locate the remains during a swimming larval stage. Once snotworms arrive, the females send “roots” into the bone. Harems of smaller “dwarf” males land on the females, taking up residence on their tube-shaped bodies and fertilizing their eggs.
At the same time, other bacteria gather in great mats and help to break down the bones. Over the slow tick of decades, the whale disappears.
Deep-Sea Time Machines
The fossil record tells us — via distinctive Osedax burrows that pockmark bone — that whale fall communities have been around for 30 million years. But some research suggests that these remote ecosystems could have extended even further into the past, before the advent of marine whales about 45 million years ago.
In 2008, Polish Academy of Sciences paleontologist Andrzej Kaim and his colleagues described what could be one of the most ancient organic falls yet known. As they analyzed a pair of 66- to 100-million-year-old plesiosaur skeletons found near Hokkaido, Japan, the researchers realized the fossilized bones of the toothy, quad-flippered marine reptiles* were surrounded by fossilized shell fragments from provannids, a type of tiny snail.
Provannids are ancient survivors. They are still with us today, and they offer a clue about what happened to Kaim’s plesiosaurs. Modern-day provannid snails inhabit ephemeral and remote deep-sea environments — cold methane seeps; hydrothermal vents that spew superheated, chemical-rich water; and whale carcasses — and their prehistoric forebears probably did the same.
“They were apparently living together with the remains of the plesiosaur,” says Kaim. “I’d been looking for this for years. We could now be sure these communities developed around the bones of large reptiles in the Mesozoic.”
There would have been plenty of food for deep-sea opportunists like the provannids in prehistoric times. Starting around 250 million years ago, several lineages of terrestrial reptiles rapidly adapted into large marine forms, including plesiosaurs and fish-like ichthyosaurs.
Even land-dwelling dinosaurs may have fed organic-fall successions of sharks, crabs, snails and bacteria. While all the dinosaurs we know of were terrestrial animals, they were occasionally washed out to sea by floods.
The San Diego Museum of Natural History displays the skeleton of the “Carlsbad ankylosaur,” officially known as Aletopelta coombsi. This poor dinosaur was found among Cretaceous-age marine sediments in California. Shark teeth and bivalve shells were scattered around the dinosaur’s bones, a hint that the heavily armored beast may have once formed a short-lived, edible reef.
“If you have a deep ocean with larger organisms swimming around the surface, dying, falling to dark, cold, oxygenated depths, you’re going to have organic falls,” Glover explains. But did they look the same millions of years ago?