By Cassie Martin
BU News Service
In January, footage of the elusive giant squid in its natural habitat aired on the Discovery Channel. Researchers captured the video in July 2012, more than a mile and a half below the surface 600 miles south of Tokyo, Japan. The last time anyone saw a giant squid alive was in 2006, when Japanese researchers caught a 25-foot female squid and brought it to the surface to photograph, but it died soon after. For a creature that usually lives 3,300 feet underwater, coming to the surface is deadly. Is it possible that the squid was a victim of the bends, an illness common to scuba divers?
The answer is no. The bends, also known as decompression illness, occurs when the diver is put under immense external pressure from deep dives then rises to the surface too quickly. The sudden release of pressure forces dissolved gasses inhaled from the atmosphere, like nitrogen, to bubble up in tissue and blood effectively starving the body of oxygen.
Giant squid don’t inhale nitrogen from the atmosphere; in fact, they don’t have a trace of gas in them. Many invertebrates use gas bladders to float and move deep underwater. However, giant squid are unique. Because the pressure in their habitat is so high, a gas bladder would implode. Since there is no gas for pressure to act on, giant squid cannot get the bends. But they have to keep afloat somehow. Instead of gas, squid re-purpose ammonium ions from their waste to keep buoyant in the water column. Ammonium ions are lighter than the sodium ions in seawater, so they avoid sinking to the sea floor or floating to the surface by adjusting the concentration of ions.
But if they aren’t affected by pressure, then why can’t they survive at the surface? Giant squid thrive in a deep, cold, and dark environment. Oxygen is hard to find deep beneath the ocean surface, but cold water has a high affinity for holding dissolved oxygen, which the squid needs to survive. The shallower the water gets, the warmer it gets and the less dissolved oxygen it holds. If a squid surfaced, its blood would become de-oxygenated and it would likely suffocate to death.
However, there is evidence that the giant squid’s mortal enemy, the sperm whale, is susceptible to decompression illness. Sperm whales are ferocious hunters of giant squid—the beaks of squid have been found in the stomachs of beached whales and scars from battle have been observed on their bodies. Whales will dive as deep as 10,500 feet and stay down for an hour or more. If they rise too quickly, nitrogen bubbles will form and cause bone damage. According to researchers at Woods Hole Oceanographic Institute, that’s just the hazard of doing business. Researchers inspected a collection of sperm whale bones spanning more than a hundred years. The researchers noticed the bones all had one thing in common—pitting and lesions, indicating the whales may have suffered chronic but mild decompression illness.