Surviving in the Harsh Midnight Zone

September 1, 2013
By Tara Haelle
The vampire squid sounds like a hostile creature from the Twilight Zone, but it’s really the environment these harmless cephalopods live in that’s hostile — the dark, cold “midnight zone.” The vampire squid lives in the middle of the ocean’s five vertical ecological zones, an area about a half mile to two and a half miles deep called the bathypelagic zone.
A vampire squid drifting in the deep sea. Credit: Monterey Bay Aquarium Research Institute, 2011

Situated between the mesopelagic zone or “twilight zone” and the abyssopelagic zone, also known as “the abyss,” the pitch-black midnight zone includes the oxygen minimum zone. Most vampire squids hang out in this low-oxygen area a mile to a mile and a half below the surface. The temperature there ranges from 39 to 50 degrees Fahrenheit, and the pressure can exceed 5,800 pounds per square inch, which is 400 times greater than it is at the sea surface.

How do these squids survive such brutal conditions? Several unique adaptations help them conserve energy. The squid is neutrally buoyant and lacks the muscles other squids use to change colors. Also, it does not have to swim to catch its food. It feeds on marine snow, the microscopic dead organisms that drift down from above.

Plus, so few animals can survive the inhospitable environment of the midnight zone that the vampire squid rarely has to defend itself. While the squid can move as fast as two body lengths per second over short distances, it cannot migrate over long distances or use the rapid escape response that most animals use when threatened. Instead, the tips of its arms and fins light up with bioluminescence while it flails its arms, zig-zags through the water and finally spews out a luminescent mucous cloud, all to confuse predators so they can’t find the vampire squid in the cold darkness. The vampire squid may have a hostile sounding name, but it’s adaptations for surviving in the harsh “midnight zone” are anything but hostile.