Rocky shores are among the most variable habitats on Earth. As tides rise and recede, seawater collects in precarious tidepools. The tidepool community endures wild swings over the course of the day, alternately baked by the sun and then deluged by cold seawater. As water evaporates from tidepools, salt builds up - or is suddenly diluted by rainwater. Despite being blasted by wind, waves and scouring sand, many species, including several varieties of kelp, make their living on the tideswept rocky shore.

The Ocean's Edge
The boundary between land and sea never stands still. As the restless tides rise and recede, shoreline habitats are repeatedly submerged and exposed, and a sudden wave can drench dry rocks at any time. Whether any given spot is under the sea or on dry land may depend simply on the time of day.

How does life fare on this frontier between land and sea?

Zonation: Layers of Life
Shoreline that is sometimes exposed to the air and sometimes buried by the tides is called the intertidal zone. Here, plants and animals are arranged in horizontal bands according to how wet they get.

The highest stripe is the splash zone, which is dampened only by the largest waves and spray. Here, barnacles cling to rocks encrusted with microscopic algae, and stringy filamentous green algae grow in splash pools.

In the middle zone, plants and animals hoard water to stay moist between dunkings. Dry, exposed mussels clamp their shells tightly shut to seal in water, and seaweeds absorb water with chemical gels. Rocks are draped with colorful, streaming seaweeds of all shapes and sizes.

The richest, deepest zone is exposed only once or twice a month, when the tides are at their lowest. Here, lush carpets of kelp crawl with blood stars, anemones, sea slugs, sponges, brittle stars, urchins and crabs.