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Next, Sanford leads his audience—in this case, me—on the short walk to Horseshoe Cove, another indentation in the rugged shoreline of Bodega Head. After a little exploration through the thick growth of kelp and sea grass, he picks up a promising-looking rock about the size and shape of a slightly melted bowling ball.

"Let's see what we can find," he says. "This yellow crust is a sponge, in the phylum Porifera. This sea anemone is in Cnidaria, and this tiny sea star is in Echinodermata. This snail and this nudibranch are both in Mollusca, and here are several tube worms, in Annelida.

"We've got a couple of things here that look something like sponges, but they're in Bryozoa. Here's a tunicate, also called a sea squirt, which is in Chordata, and a crab, in Arthropoda." It takes some searching, but he comes up with one more: "And this is a flatworm, in Platyhelminthes."

So there's the magic. Eric Sanford is holding, in one hand, representatives of more than one-fourth of all the animal life on Earth: nine phyla on one rock. In comparison, the entire land surface of the planet, from Poles to Equator, is home to only about a dozen phyla.

Sanford is actually a little crestfallen because he can't find a peanut worm, an odd thing in the phylum Sipuncula that would give us an even ten. The thrill would have been strictly numerical, though. I've already seen a peanut worm, and it has all the aesthetic appeal of used chewing gum. (I must admit, however, that the one thing it does, it does very well: extending a hydraulically powered, tentacle-tipped proboscis several times the length of its body to grab tiny bits of drifting dead stuff. Sanford calls it "this crazy sort of Dr. Seuss-like thing.")

"A lot of this diversity occurs because life first evolved in the sea," Sanford says. "And intertidal systems are really a microcosm of the ocean in general. In a tide pool, for the few hours that the tide is out, you're able to access it all."

A couple of days later, I'm rock-hopping above Horseshoe Cove with Jackie Sones, research coordinator at the Bodega Marine Reserve. "This," she says, holding up a pale orange creature about the size of her fingernail, "is a pycnogonid, commonly called a sea spider."

Through a hand lens, it does in fact resemble a spider, although one with a touch of the Michelin Man, body and legs ribbed and puffy. I can see this thing, blown up a couple of thousand times, doing battle with some outer space monster in a low-budget fifties sci-fi flick.

"It uses its proboscis to puncture sea anemones and suck out fluids," Sones says. But this minute predator has a nurturing side. Sones upends the pycnogonid to reveal a cluster of tiny spheres like whitish caviar. "The males care for the developing young," she says. "They gather the eggs from different females and hold them with specially modified legs." Pycnogonids fascinate biologists because they're one of very few types of animals in which only males care for the young.

Juvenile development of intertidal creatures varies nearly as much as their physical forms. Many go through a free-swimming larval stage lasting weeks or months, venturing into the immense ocean before settling down as adults on a patch of rock.

We kneel to examine one of those larval roamers—or rather the resulting adult. The giant green sea anemone, Anthopleura xanthogrammica, is a formidable predator, though it waits for unsuspecting prey to wander within reach rather than actively hunting. Resembling a fist-size blob of lime Jell-O out of the water, Anthopleura blooms when submerged, extending delicate tentacles around a sucking maw that swallows prey whole. Sea anemones show their kinship to jellyfish in their use of stinging structures called nematocysts, which they fire like microscopic darts to stun prey. I extend a finger as an anemone taste test and feel only a faint sticky sensation. If I were a crab, I'd be lunch.

Once they've set up housekeeping, Anthopleura and many of its neighbors in the intertidal zone show exceptional longevity, both individually and as species. Sea anemones have lived decades in laboratories without showing any discernible signs of aging, and some in the wild are believed to be 150 years old or more. "Short of predation or other fatal accidents," one reference book states, "anemones are potentially immortal."

Biologists question, though, how even highly adaptable intertidal plants and animals will respond to threats they've never known before. Local issues range from pollution and siltation due to coastal runoff to an increase in the harvest of some seaweeds, fueled by the demand for natural food.

Of far greater significance is ocean acidification caused by higher levels of atmospheric carbon dioxide. Mollusks, crustaceans, and even coralline algae are among the living things that use calcium in their structures, a process that could be impeded by higher acidity levels in seawater. Rising ocean temperatures are also a threat: Warm water holds less oxygen than cold water. National and state marine reserves can help protect against overharvest of ocean resources, but they're just as vulnerable as the rest of the seas in the face of global climate change.

In a meditation on the interconnectedness of life, Steinbeck wrote, "It is advisable to look from the tide pool to the stars and then back to the tide pool again." As a microcosm of the ocean—the nursery of all life including our own—the intertidal zone serves as another galaxy in the universe, one easily within our grasp.

Writer Mel White covered New Guinea’s Foja Mountains for the June 2010 issue. David Liittschwager’s photographs appeared in February 2010 in “Within One Cubic Foot.”
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