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The left-handed hermit crab, one of the many creatures living in Hawai'i's intertidal zone
Vol. 11, No. 6
December 2008/January 2009

  >>   Teaching Aloha
  >>   Inside Fortress O'ahu
  >>   What Lies Beneath

What Lies Beneath 

story by Catharine Lo
photos by David Liittshwager

Just north of the notorious, heaving shore break at Sandy Beach, piles of strewn lava rock create a jagged coastline that buffers the raging surf. The waves wash gently into the spaces between the rocks, creating knee-deep pools where marine life thrives. It’s a drizzly New Year’s as I crouch at the edge of a tidepool with expert Chela Zabin. We sit still, watching for movement. I delight in the fact that the task requires no skill other than simply to be present. The rule of discovery at tidepools is: The longer you look, the more you’ll see.

I poke my finger into the water, rudely disrupting a hermit crab’s afternoon nap. Small camouflaged fish whiz by. Every few moments, a tiny black snail crawls another millimeter. I begin to see colors—colonies of green zoanthids and moldy tufts of red algae.

“Some of your little kid comes out when you turn a rock over,” Zabin says as she does just that and finds a cluster of pink tunicates. She puts the rock back in place and picks up a giant, white-spotted sea cucumber. Placing it upside down in her palm, she touches the underbelly. Sticky, gelatinous tendrils cling to her index finger. Those, apparently, are its feet. This particular brown echinoderm, Actinopyga mauritiana, or loli in Hawaiian, has an anus - through which it breathes—with five inward-pointing teeth to keep out the pearlfish that like to play house in its intestines.

“Some shoot their guts out,” Zabin says, describing the violent expulsion of the digestive tract (auto-evisceration, it’s called) that occurs when some sea cucumbers get stressed. Considering the ejaculatory behavior of this organism, it’s not surprising that many cultures regard it as an aphrodisiac. An expression used in Hawaiian love sorcery goes, He loli ka i‘a, ‘iloli ke aloha. “When loli is the offering, passionate is the love.”

Before I learned anything about them, I’d always found these sand-covered sausages to be absolutely repulsive. I still think they’re disgusting, but now I’m intrigued. They and the hundreds of other invertebrates, fishes and plants in these little pools along O‘ahu’s wind-battered Kaiwi coast are wholly foreign to me. They inhabit an intricate world along Hawai‘i’s coastlines called the intertidal zone—the area between low and high tide—a habitat that is largely overlooked in favor of the more glamorous coral reefs.

Intertidal habitats take multiple forms: tidepools, splash pools, limestone reef flats, rocky shoreline and lava rock basins. Hawai‘i’s most beautiful sites feature expansive pools that reflect the sky and tame the sea—places like Shark’s Cove on O‘ahu’s North Shore and Wai‘opae Pools on the Big Island. They’re especially inviting because you can reach them on foot; some pools are even deep enough for snorkeling.

The creatures that live in these liminal worlds are bizarre, “stranger than anything you’d find in Star Trek,” Zabin says. “They’re like aliens.” Take pi‘oe‘oe, for example, a barnacle that lives with its head attached to a rock and feeds with its feet. Or the tunicates—advanced, filter- feeding animals that like humans have a beating heart, but unlike humans, reverse their blood flow every fifty beats or so. The zoanthids that resemble fat, soggy Cheerios immediately succeed the loli as the most revolting creatures of the sea. A reddish zoanthid called limu-make produces a lethal poison that warriors in Hana, Maui, once smeared on their spear tips. Ironically, this poison, palytoxin, also possesses anti-carcinogenic properties.

We might not think of these bizarre bags of jelly as animals, but according to John Hoover, the author of Hawai‘i’s Fishes and the tidepool enthusiast’s bible, Hawai‘i’s Sea Creatures: A Guide to Hawai‘i’s Marine Invertebrates, more than 90 percent of intertidal organisms are invertebrates, not plants, and they’re as different from each other as they are from humans. They have adapted uniquely to their difficult habitat. They endure dramatic changes in salinity and temperature daily. They get scorched in the sun and pummeled by the waves. Whenever the tide rises, their predators move in.

Because of these extreme living conditions, intertidal animals—some of the most elaborately designed organisms on earth—take exotic forms and possess remarkable powers. The helmet urchin fuses its spines together to form protective plates when the water level drops. The Hawaiian pom-pom crab wields stinging anemones in its claws. The cartoonish bullethead rockskipper “runs” along tidepool bottoms using its fins like legs. At low tide it will jump safely from pool to pool.

By the end of my exploration of the pools along Sandy Beach, I come to agree with what the distinguished Bishop Museum zoologist Charles Edmondson wrote in his 1949 book Hawai‘i’s Seashore Treasures: “The seashore offers storehouses of treasures that may be opened to keen and observing eyes.” My New Year’s resolution is to keep mine open.