Tide Pools

Mel White -

The sea star—often called a starfish, though it's no more a fish than it is a sheepdog—ranks with the most spectacular creatures of the diverse menagerie inhabiting the shores near Bodega Bay. Big (sometimes a foot across) and obstinately colorful (some are orange, some are purple; no one knows why), the sea star is usually found in a rock fissure sprawled like a discarded toy. But despite its apparent lethargy, Pisaster ochraceus serves as a top predator of the intertidal zone—tiger of the tide pool—though it lacks anything like a brain.

Sarah Ann Thompson, a marine biologist from the Farallon Institute in Petaluma, California, is guiding me over the rugged rocks and through the tide pools of Bodega Head's Mussel Point, 65 miles north of San Francisco. (I, in rain gear, rubber boots, and knee-pads, am trying not to slip on the shiny, slick kelp and end up as fish food.) Thompson stoops to pick up an orange star.

In a bizarre adaptation right out of a superhero movie, Pisaster can, in the span of a heartbeat—or what would be a heartbeat, if it had a heart—rigidify the "mutable tissue" in its normally limp body to transform itself into a structure as solid as bone. It then employs an internal hydraulic system and hundreds of suckerlike feet to grab the shells of a mussel and summon enough force to pull them apart.

"This Pisaster has already killed the mussel," Thompson says, holding the sea star and the deceased in one hand and separating the mussel's shells a bit with the other. "Pisaster has everted its stomach out through its mouth, and it's digesting the mussel externally."

So that creamy goo inside the mussel … ?

"Yes, that's Pisaster's stomach. When it's finished eating, it pulls its stomach back inside itself and goes on its way."

Tide pools form in zones of rocky shoreline where ocean and land meet—strips of shore, sometimes only a few yards wide, where everything is covered and uncovered by tides each day. John Steinbeck famously described this zone as "ferocious with life." The observation applies spatially—lots of things are happening in a relatively small area—but also temporally: Things happen fast between tides.

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Photo David Liittschwager

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