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Marine Life of California's Rocky Shores (Image 29)

A close up of an ochre sea star's sieve plate, or madreporite, located on the back of a sea star, just off-center. The madreporite is an opening used to filter water into the water vascular system of echinoderms. It is visible as a small red or yellow button-like structure, looking like a small wart, on the aboral surface of the central disk of a starfish. The water vascular system of the starfish consists of a series of seawater-filled ducts that function in locomotion and feeding.

While the ochre sea stars venture through the Mid Tide Zone, clearing shellfish and thus leaving room for the aggregating anemone clones, other sea stars prefer the lower reaches of the rocky shore and are most common below sea level in the Low Tide Zone. We will now leave the Mid Tide Zone and look at life in the Low Tide Zone (see "More About this Series" below, to learn more about the zones). [Image 29 in a series. See Image 30.]

More about this Series
This series of images examines the various marine life that can be found in the different sea levels, or zones, of the rocky shores of the California coast. The images were photographed by Genevieve (Genny) Anderson of the biological sciences department, Santa Barbara City College, as part of her ongoing research on the subject.

Rocky shores provide a stable substrate for plant and animal life or organisms, as opposed to sandy beaches where the substrate (sand) is constantly moving. When the tide goes out then the influences of the air and weather (sun, rain, snow) begin to play important roles--more with the higher zones.

At any tide level on a rocky shore, a pool of water--called tidepools--can be left with the receding tide. These pools provide welcome ocean water for marine life left high and dry with a receding tide. The pools highest in the intertidal may become very hot due to the sun which may not be comfortable for some species. The pools closest to the low tide have the least influence from the air and weather and thus the greatest variety of marine life. These tidepools often mirror what is actually subtidal (below the lowest low tide, as opposed to intertidal which is between the tides). As the water goes down, most of the ocean creatures go out with it, but some can't move and are left on rocks. These creatures must be adapted to withstand not only the dryness of their area, but waves, storms, wind and rain. It is their ability to withstand dryness, and their interactions with each other (eating, being eaten, competing for space and reproducing) that determine who dominates within the rocky intertidal areas.

In examining the marine life of the exposed rocky surfaces of California's shores, it is easiest to look at these rocky surfaces where they live in "zones." Above five feet, the surface is covered only by the highest high tide and thus dry three-quarters of the day. This is called the "Splash" Zone. Then, between five feet and two and a half feet, the surface is covered alternately by both high tides so it is dry between the high tides--about half a day. This band is called the "High Tide" Zone. Between sea level and two and a half feet the rocks are only left dry at the low, low tide. This area is thus dry only a quarter of each average day and called the "Mid Tide" Zone. Then there is what we call the "Low Tide" Zone, the area below sea level that is exposed for only a few hours every few weeks at special "minus" tides (remember, zero sea level is the average of the low, low tides).

To learn more about Genevieve (Genny) Anderson's research on marine life along California's rocky shores, visit her Web page, "California Tidepools (Rocky Shores)." Anderson, who has been a teacher of marine biology and biological oceanography at Santa Barbara City College for over 30 years, has other interesting lesson plans and lecture material available on her website, Here.

Credit: Genny Anderson, Santa Barbara City College

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