Jumbo squid are long-distance commuters. Every day, these gangly creatures migrate more than 500 hundred vertical feet. It's a high-energy lifestyle — and one that's going to suffer as a result of global warming, according to a new study.
Squid now appear to be joining the list of marine creatures at risk from rising levels of carbon dioxide in the atmosphere. As the oceans absorb some of this CO2 load, pH levels drop, and the water becomes more acidic.
Previous research has shown that ocean acidification makes it harder for corals, mollusks and other calcifying organisms to build skeletons and shells. The new study suggests that the effects of acidification are more complicated and far-reaching than many scientists expected.
"For the first time we've definitively proven important negative effects of high carbon dioxide levels on uncalcifying organisms like squid," said Rui Rosa, an animal physiologist at the University of Lisbon. "We've proven that CO2 will have a tremendous impact on their ability to move by the end of the century."
Not to be confused with the mysterious giant squid, which can exceed 40 feet in length, jumbo squid (Dosidicus gigas) are common and well studied. Also known as Humboldt squid, these animals can grow up to 8-plus feet (2.5 meters) long and weigh up to 110 pounds (50 kilograms). They are a commercially important fishery catch in Mexico and South America.
Jumbo squid are the only species of squid that follow their prey each night to extremely deep, oxygen-poor layers of water and return each day to feed at the water's surface.
Squid move by jet propulsion, which demands a huge amount of energy — and squid have some of the highest metabolic rates in the sea. Jumbo squid, in particular, burn a lot of gas in their 575-foot (175-meter) daily commute.
To see how ocean acidification might affect this jet-set way of life, Rosa and colleague Brad Seibel, of the University of Rhode Island, netted 86 jumbo squid in the Gulf of California. On their research boat, the researchers placed each squid in a water-filled chamber, in which they varied temperature, oxygen and CO2 levels. Throughout the experiment, they measured the animals' metabolic rates.
When the animals faced levels of CO2 projected for the end of the century, the study showed, their metabolism slowed by 30 percent. They also became 45 percent less active. Elevated temperatures exacerbated these effects.
As water temperatures and CO2 levels rise, Rosa predicts, jumbo squid will grow more lethargic, making it harder for them to catch prey and escape from predators. Their habitat range will also become compressed. Results appear in the Proceedings of the National Academy of Sciences.
The new work might help explain why Humboldt squid, once only found in tropical waters, are now showing up as far north as Alaska and British Columbia.
"I had always thought of this species as being one of the most adaptable in the ocean," said Ron O'Dor, senior scientist at the Census of Marine Life in Washington, D.C. "Now we are seeing that is being squeezed in ways no one had really appreciated."
More surprises will probably follow.
"Nothing in the ocean is safe from the impacts of global warming and acidification," O'Dor added. "Everything is going to have to make adjustments."