(truenature)

The Cauldron of Life

For the plants and animals that thrive where ocean meets
land, the world is a rough-and-tumble place.

By Paul VanDevelder/Photo by Art Wolfe

Pocket universe: Relatives of every major group of invertebrates on earth are represented in a single tidepool.

Early one summer morning, while balanced on a knife's edge of basalt high above the churning surf at land's end, I was momentarily seized by an urge to leap. Gulls, suspended all around me in effortless flight, seemed to mock my hesitation. After a paralyzing heartbeat of indecision, I stepped back. The ocean roared. Green Pacific surf exploded against the volcanic ramparts, pelting me with spray and an unbidden epiphany. Coming back to the sea is always the return ticket on a round-trip journey that began long before my birth. As I sorted through my wits, a familiar voice boomed from the eddies of ground fog that swirled across the cobbled beach, far below. "Yo, hey!" hollered my guide, John Borowski, a science teacher from Salem, Oregon. Borowski's roots were yanked out of the New Jersey shore 15 years ago, then repotted in the Pacific Northwest.

His grin flashed a thin white line of teeth as he pointed with animated excitement at something in his bearlike paw. "You've gotta see this!"

At first light on a clear June day, Borowski and I had arrived at Yaquina Head on the central Oregon coast. We weren't alone. The stream of headlights following us off U.S. 101 suggested a parade of Shriners looking for breakfast. In fact, none of us had met before. We were scientists and painters, photographers, teachers, and families from as far away as Nebraska and Colorado. What prompted our coincidental odyssey was a phenomenon Borowski calls a "monster minus," a huge tidal swing caused by an ephemeral gravitational alignment of earth, moon, and sun.

For the family of Cornhuskers, the trek to Oregon was old hat. As we set off down the narrow goat path that switchbacked across sheer-walled cliffs to the tidepools, hundreds of feet below, they told me this was their third trip to Oregon in as many years. Each January they sat around their kitchen table in Nebraska and scheduled their annual vacation to coincide with the deepest dip on the tide charts. This year it would be a minus-two-and-a-half-foot "event" beginning at 6:30 on a morning in late June, on a beach 1,500 miles away.

For marine scientists this was The Big Moment, a fleeting glimpse into the cauldron of our planet's oldest and most vital soup kitchen. For all but a few hours of the year, the lower reaches of that kitchen are fiercely hostile to hominids in sneakers. Yet for all of earth's pelagic species, all the free-swimming Nemos out there, the intertidal zone is a prodigious protein factory, the great seaside takeout window on which all these species depend for survival. Each echinoderm, for example, in a thriving community of thousands of echinoderms, or sea stars, releases several million eggs every time it spawns. A handful of those eggs will ripen in the dim solitude of the deepest region of the intertidal zone and become new members of the community. The remaining millions, a wave of protein and lipids, will be carried off by the churning surf to dozens of hungry species waiting for lunch in deeper water.

"What's fascinating," explained Borowski, "is the zonation you see between the species on these big minus tides. The competition for space in the infralittoral fringe, the midzone, is intense. In 500 million years these species have never had a day off. Somehow they've managed to achieve a remarkable level of symbiotic balance. You have to take care of your neighbor because she's probably your next meal."

Successful species have flourished by developing specializations that enable them to travel between zones. The hard-shelled chitons and soft-shelled crabs, for example, have rigid exoskeletons that protect them from drying out when the receding tide leaves them exposed to terrestrial elements like wind and sun. Creatures living in the deeper regions, such as anemones and sponges, have soft, flexible bodies that easily absorb the ceaseless pounding of the waves. Sea stars, the alpha predator of the laminaria zones, are completely dependent on the smorgasbord of infralittoral-fringe protein for their survival. In other words, they always go out to dinner. The keystone species in their restaurant of choice also happens to be the most prolific progenitor, the common mussel. Although the mussel and the star have evolved in different environments, their common survival is linked, like the robin and the worm.

"In a healthy community of mussels, we'll find 7,000 individuals per square meter," says Borowski. "Every one of those little guys filters microbic proteins from 7.5 liters of seawater per hour. That's 14,000 gallons of filtered water per hour—for one tiny community of mussels. Now, multiply that by a couple of hundred million years."

Those kind of numbers give me vertigo. Truth be told, I was the accidental tourist who had always viewed tidal zones as a kind of evolutionary skid row, a waste bin for genetic castoffs and derelicts. My long-overdue comeuppance was at hand. Borowski pointed at a fleshy, golden-colored invertebrate in the well of his palm.

"This little guy has a notochord as a larva, but he loses it when he becomes an adult. . . ."

"What's a notochord?" I interrupted.

"A spinal cord," said Borowski, "vertebrae. I have the honor of introducing you to your distant cousin, Mr. Tunicate, better known as a sea squirt."


Marine zoologists estimate that 90 percent of the world's oceans are biological deserts. The remaining 10 percent are home to more than 90 percent of all living creatures on our planet. At the edges of those oceans, in a primordial world that is neither land nor sea, the first ticks of biological time were measured in the amorphous throbbing ectoplasm of our planet's first living cells. A billion years later the ebb and flow of the tides are still the gods that rule here. Everybody eats, everybody has sex, and everybody dies. But the intertidal zone is a great deal more than a smorgasbord of protein, note Edward Ricketts, Joel Hedgpeth, and Jack Calvin, authors of the seminal work Between Pacific Tides. It is the testing ground for species, the giant mixing bowl of life, in which precise and perfect adaptation to the fierce press of elements has been the indispensable ingredient for survival for hundreds of millions of years. Myriad life-forms that flourished in this harsh environment in the Cambrian Era, 500 million years ago, are still with us today.

"Relatives of every major group of invertebrates on the planet can be found in a single tidepool," explained Borowski, hovering over a community of bright pink cnidaria, or anemones. "It's all here. We know where life started."

In the Precambrian Era the only sounds on our planet were those of wind against rock, water against sand. The essential building blocks of life—hydrogen, oxygen, nitrogen—were coming together in the intertidal zone. Fossil records show that sponges and jellyfish, worms of countless sorts, snaillike mollusks, and a host of arthropodal ancestors to the crab emerged biologically whole in the Cambrian. To get a better sense of time on this scale, hop into your car and drive about three miles. One giant pace back from your car's front bumper represents the entire anthropological time line of Homo sapiens. By contrast, life began forming in tidepools half a mile back in the rearview mirror. All these years later, give or take a million, the fact that the salinity of my blood, of my sweat and tears, is the same as the primordial soup sloshing about in these tidepools, is as imponderable as galaxies glimpsed by Hubble, and as sobering as a church picnic.

Slam a fist into your open palm, over and over again, while standing in a hurricane in February, and you have life in a tidal zone.

Yet, as I scramble from one basalt pool to the next in a state of wide-eyed wonder, I know from research and observation that the 54,000 miles of saltwater shoreline in the United States is under constant assault from a rogues' gallery of the usual suspects: deforested watersheds, shoreline developments, coastal erosion, oil spills, and pollutants of every kind. Pesticides, herbicides, and the ubiquitous nitrates of agricultural fertilizers lead the ceaseless charge. There is no longer any question, says Jane Lubchenco, a world-renowned zoologist at Oregon State University, that the rates, scales, and kinds of changes occurring in all of the earth's ecosystems are "fundamentally different from those at any other time in history."

In the past five years marine scientists have underscored these findings by identifying dozens of new "dead zones" in the world's oceans—regions where low to no oxygen disrupts normal life processes. One of the largest of those zones begins at the mouth of the Mississippi River and fans out to cover thousands of square miles of the Gulf of Mexico.

In a report in Science, Lubchenco and her colleagues warned that coastal wetlands have been altered over large areas and that "50 percent of mangrove ecosystems globally have been transformed or destroyed by human activity." Moreover, they added, a planetwide increase in harmful algal blooms in coastal ecosystems "suggests that human activity has affected the base as well as the top of the marine food webs." Today Lubchenco speaks of the global challenge of making a transition to sustainability across all ecosystems. All of the ways we're changing the planet—transforming land, modifying the climate, overfishing oceans—are "due to the way we use resources and generate waste, as well as the increasing number of people on the planet. All of those things are acting together to disrupt the ecosystems of the planet that provide life support for everything on earth."


Still, here on the Oregon coast, the intertidal zone can be explored in a pristine state. When the sea pulls back her skirts at the base of Yaquina Head, what's revealed is a world of spectacular beauty. Perched on a ledge that was under 15 feet of seawater just hours ago, I watch a tiny crab emerge from its rocky nook and take a look around. Its neighbors, a colony of pink anemones, have closed against wind and light like the iris of an eye. Voracious dog whelks have set about drilling holes into the calcified fortresses of barnacles, sucking the rich protein through tiny holes. Young crabs scavenge the shallow pools for a quick meal, and limpets, periwinkles, and chitons cling to overhanging ledges. As purple urchins and nudibranchs doze in the sun, we humans dart from one pocket universe to the next, announcing our discoveries with hurried amazement.

At the tidal swing's nadir, Borowski lets out a whoop from the edge of the surf. He has found what he has come for, a rare sunflower star, the most bashful member of the peripatetic echinoderms. If you are fortunate enough to see a sunflower star, look quickly, because a glimpse of this shy creature is also a signal from the moon and the sun that they have lost their grip on the ocean. In minutes the returning waves will chase us back to the cobbled beach and reclaim the deepest pools. There, in the timeless embrace of our planet's amniotic fluid, the most reclusive and exotic citizens of the intertidal zone will remain beyond our reach until the next "monster minus" event, sometime next year. As the silence roars around us, we gather in little knots and gaze in wonder as the crucible of life disappears beneath the gossamer flux of the sea, leaving us high and dry. And breathless. Dusted with awe.

 

PAUL VANDEVELDER's work has appeared in magazines and newspapers around the world. His new book, Coyote Warrior (Little Brown), which chronicles the 200-year story of the Mandan-Hidatsa family that sheltered Lewis and Clark during the winter of 1805, is due out in August.




© 2004 National Audubon Society
 

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The Nature of Tidepools

The intertidal zone is that narrow band of coastline between the highest high tides and the lowest low tides. Cubic yard for cubic yard, this ecosystem is the richest source of minerals and nutrients on earth. Each wave serves up a stew of plankton and algae that feeds mussels and barnacles; they, in turn, feed crabs, urchins and anemones, sponges and stars. Creatures in the highest zones take a constant pounding from wind and sea. (Slam a fist into your palm, over and over, while standing in a hurricane in February, and you have life in a tidal zone.) At the other end of the spectrum, the creatures in the lowest pools must be ever vigilant. If they get caught outside of their home zone by an outgoing tide, they will almost certainly die. A big spring "minus tide" will reveal the five main intertidal zones.

—P.V.

Splash Zones: This is where you are probably standing as you wait for the tide to go out. Take a close look. You are likely to find yourself in the company of periwinkles, a kind of snail that thrives on lichens just beyond the reach of the highest tides. This, the uppermost tidal zone, is seldom covered by the ocean. Terrestrial animals and birds thrive here if they can tolerate an occasional dousing. It is the most marginal and nutrient-poor part of the tidal-zone ecosystem.

Mid-tide Zones: Most residents of this zone, such as barnacles, limpets, crabs, and snails, have developed hard shells for protection. Prey and predator are never far apart here. Rock whelks drill tiny holes into the shells of barnacles, squirting digestive juice into the cavity, then sucking out the contents. Some common residents of this part of the intertidal zone are red, green, and brown algae, periwinkles, acorn barnacles, lichens, finger limpets, emarginate whelks, and turban snails.

High-tide Zones: This is where the action is. It is also the deepest zone exposed by an average tide. Many creatures from neighboring zones feast here among the dense clusters of blue mussels, limpets, sponges, and common anemones, whose flowerlike tentacles sting and paralyze small fish. Their jellylike bodies easily absorb the punishment of the pounding surf, while their neighbors the sea stars (starfish) have a system of internal hydraulics that allows them to suck water through tubelike feet, creating sufficient suction to cling to rocks in the heaviest weather. Other creatures here are goose-neck barnacles, purple stone crabs, hermit crabs, ocher sea stars, and sponges.

Low-tide Zones: The animals that thrive here can tolerate only limited exposure to our atmosphere. There are many exotic creatures to be found in the low zone, but they will require careful searching. Spiny purple sea urchins are common in the deepest part of the tidepool. The most exotic residents are the nudibranchs (nudi = naked, and branch = gill). These small, brightly colored creatures resemble slugs, and it takes some doing to find them, but they are well worth the effort. Nudibranchs are carnivores that feast on sponges and anemones. Here you will also encounter sculpins, giant green anemones, keyhole limpets, gumboot and mossy chitons, and crabs.

Sub-low Zones: This zone is seldom exposed to the air. However, its occupants are clearly visible during a strong minus tide. If you are lucky, you will glimpse the exotic sunflower star. This brainless, headless animal can have 5 to 24 arms and more than 15,000 tubelike feet. Sunflower stars have been found at depths of 1,500 feet. They live beside giant green sea anemones, which have thousands of nematocysts on their arms. The nematocysts paralyze sculpins and crabs, this giant’s favorite meals.