The bizarre life of the sea’s middle depths has long been a challenge to see, study and fathom. The creatures of that realm live under crushing pressures at icy temperatures in pitch darkness. The fluid environment is unbound by gravity and hard surfaces, so natural selection allows for a riotous array of unfamiliar body parts and architectures. By human standards, these organisms are aliens.
Now, a new kind of laser is illuminating some of the most otherworldly life-forms. The soft bodies of the abyssal class are made of mucoid and gelatinous materials — somewhat like jellyfish, only stranger. They feature mazes of translucent parts and gooey structures, including long filaments, mucus housings and fine-mesh filters for gathering food. Recently, in the depths off Western Australia, scientists filmed a gelatinous type known as a siphonophore whose length was estimated at 150 feet — potentially the world’s longest example of oceanic life.
On June 3 in Nature magazine, a team of seven scientists from the Monterey Bay Aquarium Research Institute in California and the Pontifical Catholic University of Chile in Santiago described an imaging device for studying these translucent creatures. It emits a thin fan of laser light that scans through the animals, gathers backscattered rays from the inner flows and tissues, and feeds those gleanings into a computer that visually reconstructs the living organisms in subtle detail. The device, called the DeepPIV imaging system, reveals the insides much as CT scans do for human bodies.
“It’s staggering,” Bruce H. Robison, a marine biologist at MBARI who participated in the research, said of the new technique in an interview. “It’s going to open things up in a really good way.”
The team conducted its explorations off the California coast in Monterey Bay, which features a deep canyon. A robot holding the imager was lowered on a long tether, resulting in the scrutiny of scores of creatures at depths of up to a quarter mile.
Kakani Katija, an engineer at the marine institute and the paper’s lead author, said the new technique would help unveil how the gooey animals do such things as move, feed, procreate and protect themselves. “Now that we have a way to visualize these structures, we can finally understand how they function,” she said.
In the Nature article, the team told of directing the novel device at an abyssal creature known as a giant larvacean, a marvel of nature that can secrete balloon-like mucus feeding structures as wide as three feet. Within a large structure are smaller, fist-size filters that the animals use to gather prey and tiny particles.
Using the new technique, Dr. Katija and her collaborators were able, for the first time, to map the structure of the larvacean’s inner filter, identifying its precise shape and the exact function of its parts. Added computer power let team members turn the visualization into a movie that enabled them to effectively fly through the filter and scrutinize its flows.
Until now, no scientist has had the chance to examine such complicated structures in the deep creatures, Dr. Katija said. Such visualizations, she and her team wrote in their paper, “can shed light on some of nature’s most complex forms.”
The paper’s other authors are Giancarlo Troni, Joost Daniels, Kelly Lance, Rob E. Sherlock, Alana D. Sherman and Dr. Robison. Except for Dr. Troni, an engineer at the Catholic university in Santiago, the researchers work at the California marine institute.
The new technique could — at least potentially — have an enormous impact on marine science, because the world’s oceans are so vast and the denizens of their inky depths so mysterious. Scientists estimate that more than 99 percent of the planet’s biosphere resides in the oceans. Fishermen know its surface waters, but in general, compared to land, the global ocean is unknown.
Dr. Robison has estimated that up to half the creatures of the sea remain undiscovered — mainly the otherworldly ones of the middle depths.
“If an alien civilization came to look at the dominant life form on the planet, they’d be out looking at midwater creatures,” he said in 1994. “In terms of biomass, numbers of individuals, geographical extent — any way you want to slice it — these are the biggest ecological entities on earth. But we know virtually nothing about them.”