Rocky Shore Biota

Plants and Animals in Rocky Areas

Splash Zone: Mostly rock is visible with a few animals visible here.

The Rock Louse, a gray-green bug-like animal, lives here and cannot tolerate being submerged. A small dirty-gray snail, the Periwinkle, is diagnostic of this zone and is plentiful on top of Flat Rock. Also present is the tiny Small Acorn Barnacle and various Limpets, These latter have gray-green to brown shells that look like flattened cones stuck to the rock.

High Intertidal Zone: Slightly more rock is covered with living things.

The Periwinkles, Acorn Barnacles, and Limpets continue and, a little lower the Black Turban Snail and the Owl Limpet are found. This limpet is like the others except that it is bigger and smoother and is often found in its own depression on the rock. Shore Crabs may be seen crawling about investigating the sessile (attached) inhabitants. Hermit Crabs may also be seen. Chitons, stationary slug-like animals with segmented shells, are conspicuous. Rockweed as well as Red and Pink Encrusting Algae. starts to be evident.

Middle Intertidal Zone: At least half the rock is occupied by attached life.

At the high end of this zone are mussel beds, and the lower limit is marked by green surf grass. The most conspicuous assemblages of this zone are the aggregates of California Mussel and necked Goose Barnacles. Also seen at Flat Rock are honeycomb-like Sand Castle Worms, which build their houses out of cemented sand grains.

Below the mussel beds are many more organisms. The Aggregate Sea Anemone is present where the mussel bed is not well developed. This anemone may occur in colonies of thousands of individuals and is covered by shell fragments and other detritus. These anemones are squishy and wet when out of the water but open into a concise and beautiful flower-like patch when submerged. A close relative is the Giant Green Anemone which lives usually as a solitary individual Anemone and is larger than the Aggregate Anemone.

Also found in this zone are two medium large barnacles. One is the Pink Barnacle with pink stripes on the shell and the other is the Thatched Barnacle, which is more conical, has a smaller opening, and tends toward a more solitary habit.

The snails of this zone are the Purple Olive, which often leaves its tracks in the sandy-bottomed tidepools, the Gem Murex, found on rocks, and the California Cone. Coffee Bean Shells also occur here, as well as Volcano Limpets. Occasionally a large, dark purple sea slug, the Sea Hare, may be seen here.

Common tidepool fish in this zone and below are the Wooly Sculpin and the Opaleye.

Plants in this zone are the pink encrusting California lithothamnium, which lines the bottoms of many tidepools, the Circular Pink Alga, which forms small circular pink patches, and several forms of what are known as Coralline Red Algae with their small and jointed branches. The brown seaweeds of this zone are the long Feather Boa Kelp and the stiff Sea Palm.

Low Intertidal Zone: Almost all rock is covered with plant life.

You know you’re in this zone because of the predominant seaweed known as Green Surf Grass, which flourishes from this level to as deep as twenty feet subtidally. This is not an alga but is actually a flowering plant which has become adapted to a marine habitat. It forms large, emerald-green masses on rocky bottoms and is commonly confused with Eel Grass by the layman. True Eel Grass lives intertidally in bays and estuaries where there is little or no wave shock and occurs as deep as 100 feet subtidally on muddy substrates.

Many of the same animals which live in the middle intertidal zone also live in the low intertidal. In addition, many subtidal animals may be found in this zone. Examples are the Spiny Lobster, young Moray Eels, brick red to purple Kelp Crab, and a rare sea star (more commonly known as Starfish).

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