Ocean’s mysteries the focus of Fernbank film

Fernbank Museum of Natural History only: $18 for adults, $17 for seniors, $16 for children ages 3-12, and free for 2 and younger (on a space-available basis).

Imax tickets only: $13 for adults, $12 for seniors (65 and over), $11 for children ages 3-12, $8 for Fernbank museum members, and free for children 2 and younger (on a space-available basis).

If you buy museum admission and Imax together as a value pass: $26 for adults, $24 for seniors, $22 for children, $8 for members, and free for 2 and younger (on a space-available basis).

Open daily, 10 a.m.-5 p.m. Fernbank Museum of Natural History, 767 Clifton Road N.E., Atlanta. 404-929-6300 (info) or 404-929-6400 (tickets), www.fernbankmuseum.org.

It is no less than the greatest migration of animals on the planet. And it takes place nightly.

In swarms too vast to count, plankton rise to the surfaces of the world’s oceans to feed. Close behind are the larger animals that eat them. Even greater creatures that dine on plankton’s predators aren’t far away. Thus does the chain of life stretch across the seas.

The intricate foundation of Earth’s seas is the focus of “Jean-Michel Cousteau’s Secret Ocean,” the latest Imax feature bowing this month at the Fernbank Museum of Natural History. The film runs June 19-Sept. 24.

The museum had a sneak showing Tuesday, wrapping up the presentation with a Skype question-and-answer session with Cousteau, who produced “Secret Ocean.”

Filmed underwater, the movie features Cousteau, whose father, Jacques, pioneered underwater exploration. With him is marine biologist Holly Lohuis. Cameras follow the two as they swim, fins moving gently past reefs and shipwrecks. Its narrator is famed marine biologist Sylvia Earle, who is no less than National Geographic’s explorer in residence.

The film, three years in the making, follows the diving duo as they prowl sea floors from the Bahamas to Fiji. It is a colorful, compelling jaunt that takes a close look at some of the oceans’ smaller residents.

Consider the Christmas worm, growing on a reef in the middle of a cobalt sea. It resembles a flower, its petals moving with each pulse of the current. When plankton float past, those petals turn into something deadlier.

Another subtle predator is soft coral. Growing upside-down on the boom of a sunken vessel, it looks like wheat, waving in the wind. Plankton that get caught in those living fronds don’t come out.

An even better hunter, says Earle, is the basket star. It looks nothing like its namesake. Instead, it resembles a tree limb that has grown out of control, with twigs curling in all directions. And so it remains, immobile — until night comes to the deep.

Then, those twigs stir. They unwrap themselves from each other, and the basket star begins moving. A mature specimen may get to be 3 feet long. When it sights prey, Earle says in the film, “it has only to reach out.”

The film also notes that some creatures form symbiotic, or mutually beneficial, relationships. For example, the clown fish (Remember “Finding Nemo,” the kids’ movie about a wayward fish? That’s a clown fish.) finds a home in the wavy tentacles of a sea anemone. The fish feeds on small invertebrates that might harm the sea anemone. The host anemone’s tentacles repel animals that might make a meal of the clown fish.

The ocean has the equivalent of a Hoover upright vacuum, too. The sea cucumber is an ungainly thing, lumbering across rock and shell. It looks like a poorly designed monster from a 1950s horror film, but it has a lovely purpose, Earle says. It sucks up the dead remains of creatures that have sunk to the sea floor.

“It is the janitor of the sea,” she says.

The most compelling creature in “Secret Ocean” may be the octopus. The camera follows one as it squeezes out of an impossibly small hole. Then, with each tentacle curling and moving independently of the others, the octopus glides over coral and stone. As it moves across a varying seascape, the octopus changes color, gray-white-blue-black-white, nearly as quickly as you read these words.

The octopus, says Cousteau, is one of his favorite sea creatures. It also fascinated his dad.

The most fascinating shot? That comes near the end. Cousteau and Lohuis find themselves on a flat stretch of sand. Ringing them are hammerhead sharks, each easily the size of the two-legged intruders. One approaches Cousteau, then stops. Cousteau halts, too. In the immensity of the ocean, Sphyrna mokarran and Homo sapiens appear to share common ground. The sight is, unexpectedly, moving.

The lesson from the film? Cousteau, who fielded questions for a half-hour after the show, was succinct:

“The future of the ocean is our future,” he told about 100 people who stuck around after the 40-minute film’s credits ran. “If you protect the ocean, you protect yourself.”