Methane-snacking crabs suggest they are adapting to climate change: report

Crabs that have a normal diet of a type of plankton have been seen munching on methane-filled bacteria off British Columbia's coast in what experts say could be their way of adapting to climate change.

Researchers with Oceans Networks Canada and Oregon State University discovered the snow crabs using other food sources because their main meal may be disappearing with a warmer climate.

The crabs were previously thought to exclusively eat phytoplankton but researchers said in a study published this month in the journal Frontiers in Marine Science that there is first evidence that the commercial species is finding some of its nutrition from other food sources.

Senior scientist at Oceans Networks Canada, an initiative of the University of Victoria, and the study's co-author Fabio De Leo said by collecting these specimens, researchers can learn how a variety of sea-dwelling species are adapting to ongoing changes linked to climate change.

"It was really funny when we first saw this," he said.

"The crab had accumulation of methane under its body and was sifting through the mud trying to collect the bubbles and they got trapped under its (shell) and then it got a lift off from the sediment."

Phytoplankton are single-celled micro algae. When they die they sink to the sea floor and form a carpet making up the main food source for these crabs.

Climate change models show that as the oceans get warmer there will be less of that food for the crabs.

"The crab might be eating more of the methane-filled bacteria and less of the phytoplankton," De Leo said.

Snow crabs are found from California to Alaska at depths ranging from 300 to 2,000 metres.

"They are quite a deep water species," De Leo said.

The researchers have watched these crabs on seeps, areas on the ocean floor where methane gas seeps out.

These methane seeps support a variety of species including clams and mussels that rely directly on the energy provided by the seep bacteria, he said.

"The clams and mussels that live on the seeps have bacteria in their guts that digest the energy. Crabs are not seep endemic," he said. "The implication is that they are using much more of the seep than previously understood."

De Leo said there's a food-chain connection and it means humans are benefiting from the methane fossil fuel.

"It's bubbling out of the sea floor and the crabs are using that and humans are using the crabs as a source of protein."

The next step in the study is to collect more crabs at different seep sites, where the intensity of methane seepage varies, giving researchers a broader perspective, he said.

Scientists also want to conduct further studies to understand how the enzymes that digest methane and bacteria are affecting the crabs.