DURHAM, N.C. -- Giant and colossal squids have eyes as big as basketballs, and a Duke scientist thinks he knows why.
"They're most likely using their huge eyes to spot and escape their predators, sperm whales," said Duke biologist Snke Johnsen.
Johnsen collaborated with a group of biologists to model, both physically and biologically, how and why a squid uses such a big eye. The team found that the design and size of the eye give squids the ability to see approaching sperm whales as they disturb bioluminescent organisms. The study appears in the March 15 Current Biology.
Big squids come in two types -- giant and colossal. They can grow to weights of five adult men put together, which is comparable to a large swordfish. But swordfish eyes are about the size of softballs, about 3 inches in diameter.
"It doesn't make sense a giant squid and swordfish are similar in size but the squid's eyes are proportionally much larger, three times the diameter and 27 times the volume," Johnsen said. "The question is why. Why do giant squid need such large eyes?"
To explain the squids' eye size, Johnsen and his collaborators first measured giant and colossal squid eyes using photos and captured animals. They also found data on the water clarity and amount of light at the ocean depths where the squid live -- typically 300 to 1000 meters. Using this information, the scientists began to mathematically model how the creatures' eyes would work and what they could see.
The team found that the squids' large eyes collect more light compared to animals of similar size but with smaller eyes. The extra light intake improves the squid's ability to detect small contrast differences under the dim conditions of the deep ocean, they argue. Johnsen said this ability doesn't matter much to the majority of deep-sea animals, which are looking at small objects that become too small to see before they fade away.
But the boos
|Contact: Ashley Yeager|