Tanner crabs dine on bacteria that derive energy from digesting methane.University of Victoria - Ocean Networks Canada/University of Victoria - Ocean Networks Canada
In the deep ocean some 50 kilometres off the coast of Vancouver Island, a group of Tanner crabs is foraging for food.
Suddenly, one of the crabs rises from the sea floor as if it is hoisted by an invisible force. A moment later, the crab flips over, releasing a large bubble of methane gas from beneath its carapace. It plunges back down, does a faceplant in the silt, then returns to its business – muddied, but seemingly unperturbed.
The curious scene was captured on video at a deep-sea station operated by Ocean Networks Canada, a federally-funded organization that supports marine science. Equal parts Jacques Cousteau and Charlie Chaplin, the video was the clue that led to a newly discovered link between the methane that is seeping out from under North America’s submerged western rim and some of the seafood that finds its way onto restaurant menus.
The curious scene was captured on video at a deep-sea station operated by Ocean Networks Canada, a federally-funded organization that supports marine science. A team of Canadian and U.S. scientists investigated what attracts the crabs – a migratory species – to this fizzy stretch of the ocean floor. After years of study, the scientists say the crabs are not there by chance, but to dine on bacteria that derive energy from digesting methane.
Ocean Networks Canada
The link was uncovered when a team of Canadian and U.S. scientists investigated what attracts the crabs – a migratory species – to this fizzy stretch of the ocean floor. After years of study, the scientists say the crabs are not there by chance, but to dine on bacteria that derive energy from digesting methane.
The finding means that the crabs are acting as conduits for channelling food energy from a fossil fuel source into the rest of the marine ecosystem. What makes this especially interesting is that Tanner crabs are marketed and consumed in the United States as “snow crab.” (In Canada, the same term refers to another, related species.) Like the crabs, the people who eat them are also getting a fraction of their caloric intake from the methane bubbling up from the briny deep.
“Humans are benefiting from this directly,” said Fabio De Leo, biological oceanographer at the University of Victoria who was involved in the discovery. In a study published last week in the research journal Frontiers in Marine Science, Dr. De Leo and his colleagues note this is the first time that a commercially harvested species has been shown to derive some of its nutritional value from chemical energy instead of exclusively through the larger ocean food chain that is based on phytoplankton – floating microorganisms that live off of sunlight and play the same role as plants in terrestrial ecosystems.
HIDE AND SEEP
The two deep-sea stations operated by Ocean
Networks Canada at the edge of the western
continental shelf have proved ideal locations for
studying the unusual ecosystems around meth
ane seeps.
Study areas
BRITISH
COLUMBIA
Pacific
Ocean
Vancouver
Island
0
75
Clayoquot
Slope
Vancouver
KM
Nanaimo
Barkley
Canyon
WASH.
Victoria
Methane seeps
Unlike deep-sea vents, which expel water that
has been superheated by volcanic activity
beneath the seafloor, methane seeps are cold
flows of methane-rich water driven by pressure
from the movement of the North American
continent.
Flipping out
Tanner crabs, foraging for food near these seeps,
rise from the seafloor on these invisible currents
of water, flip over, releasing bubbles of methane
gas from under their carapace, then return to the
seabed.
Methane
bubble
released
Crab rises
and rolls
over
Tanner crab
(Chionoecetes
tanneri)
Methane
seep
Foraging
crabs
Seafloor
IVAN SEMENIUK AND JOHN SOPINSKI/THE GLOBE
AND MAIL SOURCE: frontiers in marine science;
TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU
HIDE AND SEEP
The two deep-sea stations operated by Ocean Networks
Canada at the edge of the western continental shelf
have proved ideal locations for studying the unusual
ecosystems around methane seeps.
Study areas
DETAIL
CANADA
BRITISH
COLUMBIA
U.S.
Pacific
Ocean
Vancouver
Island
Vancouver
Nanaimo
Clayoquot
Slope
Victoria
WASH.
Barkley
Canyon
0
75
KM
Methane seeps
Unlike deep-sea vents, which expel water that has been
superheated by volcanic activity beneath the seafloor,
methane seeps are cold flows of methane-rich water
driven by pressure from the movement of the North
American continent.
Flipping out
Tanner crabs, foraging for food near these seeps, rise
from the seafloor on these invisible currents of water, flip
over, releasing bubbles of methane gas from under their
carapace, then return to the seabed.
Not to scale
Methane
bubble
released
Crab rises
and rolls
over
Tanner crab
(Chionoecetes
tanneri)
Methane
seep
Foraging
crabs
Seafloor
IVAN SEMENIUK AND JOHN SOPINSKI/THE GLOBE AND MAIL,
SOURCE: frontiers in marine science; TILEZEN; OPEN-
STREETMAP CONTRIBUTORS; HIU
HIDE AND SEEP
The two deep-sea stations operated by Ocean Networks Canada at the edge of the
western continental shelf have proved ideal locations for studying the unusual eco-
systems around methane seeps.
Study areas
DETAIL
CANADA
BRITISH
COLUMBIA
U.S.
Pacific
Ocean
Vancouver
Island
Vancouver
Nanaimo
Clayoquot
Slope
Victoria
WASH.
Barkley
Canyon
0
75
KM
Methane seeps
Unlike deep-sea vents,
which expel water that
has been superheated
by volcanic activity
beneath the seafloor,
methane seeps are cold
flows of methane-rich
water driven by pres-
sure from the move-
ment of the North
American continent.
Methane
bubble
released
Crab rises
and rolls
over
Tanner crab
(Chionoecetes
tanneri)
Flipping out
Tanner crabs, foraging
for food near these
seeps, rise from the
seafloor on these
invisible currents of
water, flip over, releas-
ing bubbles of meth-
ane gas from under
their carapace, then
return to the seabed.
Methane
seep
Foraging
crabs
Seafloor
Not to scale
IVAN SEMENIUK AND JOHN SOPINSKI/THE GLOBE AND MAIL, SOURCE: frontiers in
marine science; TILEZEN; OPENSTREETMAP CONTRIBUTORS; HIU
And the crabs are probably not alone, Dr. De Leo said. “We certainly think that some other species, including rockfish, might be doing the same thing."
While certain species have long been known to live off methane seeps, these species tend to be fixed in place, living separately from other ocean life, as though on another world. The new finding suggests the seeps may be playing a bigger role in ocean biology than originally thought, thanks to the crabs and other itinerant creatures that are dropping in to supplement their diets and then moving on.
“There are certainly a lot [of] commercially important species that hang out at seeps,” said Lisa Levin, a professor at the Scripps Institution of Oceanography in San Diego, who was not part of the study.
Recent advances in underwater mapping have shown that the seeps are a widespread phenomenon. In the past two years alone, more than 1,000 such seeps have been discovered along the Cascadia subduction zone, which runs parallel to the West Coast from northern California to British Columbia. Each seep is a patch of seafloor, tens to hundreds of square metres in size, where cold, methane rich water is flowing out due to pressure from the relentless slide of the North American continent overtop the thinner ocean crust that lies to the west.
The video led to a newly discovered link between the methane that is seeping out from under North America’s submerged western rim and some of the seafood that finds its way onto restaurant menus.Ocean Networks Canada
Ocean Networks Canada operates two stations near methane seeps, both of which are hooked into an 840-kilometre-long fibre-optic loop that carries data and live video back to shore. Researchers working with the data first noticed the crabs and their flipping antics back in 2012.
“You could see that they were actively foraging amongst the bubbles,” said Sarah Seabrook, a doctoral student at Oregon State University who set about looking for a link between the crabs and the gas-guzzling bacteria.
Ms. Seabrook said she was stymied at first because when she chemically analyzed Tanner crabs that were captured at the Canadian seeps, she did not find the carbon isotopes that would be expected from geologically produced methane. Only when she looked specifically at the fatty acids in the captured crabs did Ms. Seabrook finally spot the telltale chemical signature.
“We’ve been trying to find one needle in a haystack of food sources,” she said.
Dr. Levin said the result is an important one because it shows that the impact of the seeps on the ocean ecosystem has largely been hidden until now.
The result sets the stage for a more detailed examination of life at the seeps and the way it disperses energy into the parts of the ocean environment that are used by humans.
“We are showing a link to a deep-sea environment that is often thought of as remote, but it’s connected with us,” Dr. De Leo said.
Ivan Semeniuk