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  National Geographic website, 25 Jul 05
Watch Your Step: Study Shows Life in Tidal Areas at Risk
John Roach

A clamber along a rocky tidepool may seem like a harmless way to while away the hours during these dog days of summer.

But some marine scientists urge caution on behalf of the organisms that live there. The organisms that live in the intertidal region—the zone where the ocean meets the land—appear a hardy lot at first glance: They're pounded by the surf, live in and out of water, endure extreme temperature changes, and are blasted by sunlight.

A few human footprints are the least of their worries, right?

That's a common misconception, said Fiorenza Micheli, a marine ecologist at Stanford University's Hopkins Marine Station in Pacific Grove, California. Her ongoing research shows that intertidal organisms are under constant strain, and the strain is only worsened by the intrusion of humans.

"They are already stressed by a harsh natural environment," she said. "So instead of being pre-adapted to the stress and more resistant, they are basically already at the edge and are pushed over the edge by additional stresses they haven't evolved with."

Jane Lubchenco, a marine ecologist at Oregon State University in Corvallis, said human disturbance is more than what many intertidal plants and animals can cope with.

The evidence is as simple as a side-by-side comparison. "If you go to sites where it's difficult to get to or where people have been actively excluded for one reason or another, say a military base, there is a night-and-day difference between those areas and areas just up and down the coast," she said.

Careless Trampling

According to Micheli, people tend to be unaware of the variety and abundance of life in the intertidal region. "Many intertidal organisms are attached to the rocks so they won't be swept off by waves," Micheli said. "If their attachment is weakened and then a waves come in, they will be dislodged and that's it. They're washed off."

Given the hard-fought battle these organisms endure to survive in rocky shores, they may not return for several years once removed. And their absence can change the entire structure of an intertidal community.

Lubchenco noted that factors as varied as temperature, wave conditions, predation, and competition all shape the structure of intertidal regions.

When people trample on tidal life, they not only kill the plant or animal but also send a destructive ripple through the intertidal community, she explained.

"One other thing humans do is introduce new species at much greater rates than appear naturally, and many of these like non-native species are either eating or out-competing the natives," the marine biologist said.

Low Impact

The human impact on intertidal regions is clear, Lubchenco added, but "that doesn't mean they should all be totally off limits, because clearly these are great places for people to go and appreciate and just experience."

To protect the intertidal regions, Lubchenco recommends the establishment of a network of marine reserves—areas of ocean and coastline that are protected from human activities such as fishing, plant collecting, and oil and gas drilling.

"Scientists have discovered that when areas are designated as no-take, they often rebound in a way that is surprising, because it wasn't obvious there was an impact to begin with," she said.

Micheli's research goals include the identification of candidate habitats and locations for protection as marine reserves.

She said certain fragile communities, such as some exposed headlands covered in mussel beds, ought to be protected from all human uses.

She encourages people to visit the remaining intertidal zone regions but asks that they tread lightly. "Be aware and cautious of the fact that we're walking on living things," she said. "Be careful not to step on them, not to pick to pick them up and displace them from where they live, not to alter their habitat."

Researchers too need to heed this advice, Micheli added.

Many budding marine biologists turn over boulders to see what lives beneath them, she pointed out. After they are done, they should replace the rock exactly as they found it.

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