for National Geographic News
The underwater Manhattan depicted in the animated movie Shark Tale, with its skyscrapers and trendy restaurants, may exist only on the silver screen.
But the story, about a tiny cleaner fish that dreams of climbing the social ladderand getting the right "girl"on a reef terrorized by sharks, may not be that far-fetched.
Real everyday life underwater is about survival and mating. To mix a metaphor, it can be a dog-eat-dog world.
"There's a constant struggle that goes on" to get ahead among fish, said Mike Heithaus, a marine biology professor at Florida International University in Miami. "But we don't know a whole lot about [their] social order."
The main character in Shark Tale, Oscar (voiced by Will Smith), is a cleaner wrasse, a tiny fish with blue stripes and an elongated body. He is told that he ranks at the bottom of the sea hierarchy.
In real life, there may not be an actual sea hierarchy.
"It's more of an interconnected web than a hierarchy," Heithaus said. "People think of it as a food chain, but that doesn't describe the diversity of interactions that are found in marine systems."
Helping other fish, for example, keeps the cleaner wrasse alive. As its name implies, the species cleans other fish, including large predators that may have otherwise eaten the cleaner wrasse.
"It's never a good thing to kill your doctor," said Heithaus, who has hosted a National Geographic Channel TV series on Crittercam and received research funding from the National Geographic Society's Committee for Research and Exploration.
Coral reefs, home to more than 25 percent of all marine species, are vital to the survival of over 4,000 fishes and thousands of plants. Corals are composed of tiny, fragile organisms called coral polyps (and the skeletons they leave behind when they die). Marvels of integration, the reefs are like bustling undersea communities.
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