Keith Ludemann’s fascination with marine life and the natural world dates back more than a half century, even before the Navy brought him to Whidbey Island in 1962.

But his full appreciation for such creatures can be traced back to one day in the 1980s inside a small building in Coupeville not far from the sea.

“The octopus is the most intelligent animal in the world that does not have a backbone,” Ludemann said, recounting his tale to a group of fifth graders this week during the marine biology class he teaches inside the Sea Lab at the Camp Casey Conference Center.

On that day, three decades ago, Ludemann was preparing to feed a giant Pacific Octopus that he and his son had caught, placed in a large aquarium and grown quite fond of.

At 16 feet in diameter, the octopus had a massive reach and learned to shake Ludemann’s hand.

But when Ludemann presented a crab for breakfast to the octopus, then playfully pulled it back, the fun was over as the octopus latched on to his arm and a new level of respect was born.

“I came off the floor,” Ludemann said.

“I said, ‘OK. OK. You can have your crab.’”

In more than 30 years of sharing his passion for sea life at the Sea Lab, it is one of Ludemann’s favorite stories.

After retiring from the Navy and then retiring as caretaker of the Camp Casey campus of Seattle Pacific University, Ludemann has continued to teach young visitors about the sea.

“He can seem to be kind of gruff, but then you get to know him,” said Robyn Myers, manager of conference services at Camp Casey and the Fort Casey Inn. “The kids love him.”

Wide-eyed students from the Tahoma School District crammed inside the Sea Lab Monday to kick off a new season that will stretch into June for Ludemann.

Marine creatures such as sea cucumbers, crabs, sea urchins, octopuses, sea slugs, a wolf eel and lingcod were collected by divers just offshore in Admiralty Inlet over the weekend and were put on display in open basins and large aquariums for students to see and derive knowledge.

Seawater is pumped from the nearby Puget Sound into the basins to keep the water fresh and circulating for the benefit of the creatures, which are all released back into the Sound at the end of the season.

Through enough college courses that could have landed him a degree in marine biology had he pursued it, Ludemann has acquired a vast sea of knowledge that he shares to enlighten children’s lives and enrich his own.

He got motivated to teach kids about the proper treatment of marine animals after witnessing instances of abuse decades ago.

“They’re God’s creatures,” he said. “He put us here to take of this stuff, not to use and abuse it.”

Ludemann, who lives in Oak Harbor, had little trouble keeping students’ attention Monday as he displayed sea animals and shared facts about them.

He carried around a crab that lifted a cap off a child’s head with its pincher, a sea cucumber that squirted water and a massive moon snail that rested in his hands.

“The moon snail is a carnivore,” Ludemann said. “They drill holes through clam shells and then they eat the clam.”

Ludemann figures he’ll teach more than 100 Sea Lab lessons this season as part of the outdoor education offered to campers and day-trippers from nonprofit groups at Camp Casey. The Sea Lab class is offered separately at $50 per group.

It’s a labor of love for the man from Moorhead, Minn., whose interest in nature started the moment he was stung by a bee as a young boy.

Now, he’s dodging crabs’ pinchers in order to educate kids, along with lighter tasks.

He reached into the saltwater tub and pulled out a living sponge, a bottom-dwelling creature.

“No, it’s not SpongeBob!” he told the students with his gruff voice. “It doesn’t have square pants.”

n For information about the Sea Lab, call 360-678-5050 or go to www.spu.edu/casey