sharks migrating north and close to shore have closed beaches and frightened vacationers. with 3/4 of our planet under water, the main attraction lies beneath the surface. the diversity of life in the oceans is staggering. there are whole groups of organisms that have no counterparts on land. reporter: creatures on the lower end of the food chain have developed astounding ways to protect themselves. the simple jellyfish with its stinging cells thrive. and the blanket octopus can actually detach one of its lovely limbs as a decoy. and of course, there s always the ink. but even evolved defenses don t always work. this enormous school of lantern fish does nothing to stop the spinner dolphins who push them to the surface where there is no escape. krill form a dense ball, which makes it harder for small fish to find a target but allows the blue whale to gorge. they can t escape the blue whale. which evolved to eat them. scientists call it the evolutionary arms race. the prey have got