duminică, 7 septembrie 2008

Colossal Squid's Size Key to Survival

Big, For Good Reason

Big, For Good Reason

- The frozen colossal squid that was thawed this week shrank drastically due to water and temperature changes since it was accidentally caught by fisherman in 2007, according to officials at The Museum of New Zealand Te Papa who revealed the exact size of the squid on Thursday and believe it is still the world's largest known squid.

View a slideshow of the colossal squid here.

After waiting for the tentacles to defrost so the squid could be fully extended, the researchers measured its weight at 1,091 pounds and its length at nearly 14 feet.

The squid's heft and large beak "confirm that it was almost certainly longer and is still the largest invertebrate specimen in the world," Te Papa spokesperson Jane Keig told Discovery News.

She added that it also has the largest eye of any animal at about 10.5 inches in diameter.

Other Ocean Giants

Colossal squids exemplify a phenomenon known as deep-sea gigantism, which is the tendency for invertebrates, crustaceans and other creatures of the deep to grow to become much larger than their shallower water counterparts. Some squid, in contrast to the colossal, are just a few inches long.

Dutch biologist Olaf Blaauw, who traveled to New Zealand to analyze the enormous squid, told Discovery News that whales serve as other obvious examples of gigantism. Sharks may grow to extreme lengths too.

"A whale shark can attain a length in excess of 45 feet," he said. "Basking sharks get over 30 feet…There are probably deep water shark species yet undiscovered, based on anecdotal evidence and further strengthened by the discovery of the 15-feet megamouth shark relatively recently."

He added that ocean sunfish also grow to be very large at 10 feet long and high, and weighing up to 2 tons -- "probably the heaviest bony fish around."

Another possible member of the colossal group is the giant leatherback sea turtle, which can grow to around 8 feet in length and weigh close to a ton. Japanese spider crabs and oarfish (a type of herring) also exhibit gigantism, along with other types of squid and octopi.

Why So Big?

From a Darwinian fitness perspective, "if any attribute favors survival, it will be preserved in a species until circumstances change to make another random change in shape, form or behavior more favorable," Blaauw said.

The size of these deep-sea monsters therefore somehow improves their longevity and rate of survival.

One obvious reason is that a big body can be intimidating to other animals.

"Suffice it to say, there is little out there that can tackle a thousand-pound squid armed to the beak with powerful arms, each lined with vicious hooks and suckers," Blaauw said.

Aside from humans, the colossal squid's only other natural enemies are the occasional large shark and sperm whales, which seem to have a real taste for the cephalopod giants because they hunt them voraciously. Researchers aren't even certain that a shark can actually kill a colossal squid. Large squid remains have been found in shark stomachs, but it's possible the sharks just scavenged their already dead remains.

Size Affects Eating

Whether on land or in the ocean, an animal's size appears to predict how and what it eats. Scientists first began to make this correlation after they noticed that particularly large creatures are more vulnerable to habitat changes than smaller animals are.

John Haskell of Utah State University and his colleagues developed a computer model to explain why that's the case. They discovered the way an animal forages can be directly linked to its length and weight.

"What we found is that an organism's body size is a key determinant of how often it can be expected to encounter food in its environment," Haskell said. "Resource density is often scale-dependent, that is it changes with the scale of measurement. The food density you see at one square meter changes when you zoom out to one square kilometer."

In essence, a tiny squid looks at the world a few inches at a time, while a colossal squid must look at potentially miles at a time, perhaps somewhat explaining its gigantic eyes. Prey appears to be more sparse and patchy for larger animals, which need to cover expansive territories to get their fill.

If predictions made by Haskell's model hold up, the more the colossal squid's habitat becomes fragmented, the larger its home range will become, potentially causing the squid to grow even larger and to travel longer and longer distances for food.

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