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Tide Pools and the Life Within Them

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I have lived by the ocean all my life and I was always very interested in the creatures that live by the seashore. My favorite beach is Doheny State Beach and I go there every summer. I always go at low tide and wade through the tide pools to find creatures. Twice a day the tide retreats and leaves all kinds of interesting creatures clinging to rocks or trapped in pools of water that collect around and between rocks. These pools are called tide pools. Tide pool animals are very well adapted to their ever-changing world of sand and surf. Almost every day of the summer I go to Doheny and search the tide pools for crabs, hermit crabs, limpets, snails, periwinkles, mussels, sea stars, chitons, sea urchins, and what I like to call sea slugs. By carefully turning over a few rocks and looking in shells I find these incredibly interesting creatures.

Life forms within a tide pool (Click to enlarge.)


Doheny State Beach has a visitor center at the front of the park. The first thing I do on my expedition is go there. Inside, there is an indoor tide pool with many creatures such as sand sharks, sea stars, anemones, sea urchins, and a wide variety of fish. Salt water circulates through the tide pool to give the effect of waves and also to move small bits of food around the tide pool. There are also a few books in the visitor center that give some basic information about tide pools. I pick up a booklet that makes it easy for me to know what time high tide and low tide occur. All I have to do is look up the date and the high and low tide times for that day are listed. Now I know when to come and observe the tide pools.

I want to know about the creatures and the area they live in more thoroughly so I go to my local library, Aliso Viejo Branch Library. The library is a great place to go to find books about how tide pools form and the names and activities of the animals in tide pools.

 

September 14, 2000
It is 12:28 pm and the beach is deserted because of the cold weather. Doheny State Beach is closed because of the bacteria levels in the water. The first thing I see when I walk out onto the beach is rocks. When I look closer I see colonies of hermit crabs, snails, periwinkles, and mussels.

Hermit crabs have shells that serve as their houses. They have a hard covering called an exoskeleton on their front, and the rest of their bodies would be unprotected if they didn't have a shell. Hermit crabs live in abandoned snail shells. As they grow, hermit crabs move out of their small shells and into bigger ones. Hermit crabs are not the only shelled animals I see, though. Snails also live in shells.

Snails are a type of mollusk. Mollusks are a group of soft-bodied creatures that are usually protected by shells. Snails have tentacles on their heads and have one "foot" for walking and digging. They can pull in their "foot" and close the opening in their shells with a disc called an operculum. Snails are scavengers and grazers. They have sharp teeth on their tongues that shred food. Some snails can drill through the shells of other mollusks.Periwinkles are another group of animals I see on the rocks.

Periwinkles are a smaller species of snail. Rough periwinkles spend so much time out of the water and on the rocks that their gills take oxygen from the air.

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From left to right: A hermit crab emerging from its shell; Sea urchin; Striped shore crab; Sea anemone


Another animal I see is attached to the rocks. Mussels are a type of bivalve mollusk. Bivalve mollusks have two shell sheld together by a hinge. These creatures spin strong threads from their feet that "glue" them to rocks or other mussels. Once a mussel is attached to a rock, it stays there forever. When it is high tide, mussels open their shells and filter out tiny plants and animals from the seawater to eat. When it is low tide, mussels close up and wait until high tide. It is getting late and the tide is starting to come in and the tide pools are disappearing. I plan to comeback next week and observe different creatures.

 
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Sunset at Doheny State Beach - Dana Point, California


September 22, 2000
Today I am here at 4:40 pm. The peak of low tide is at 4:51 pm, but the tide pools are starting to form and the animals are emerging from their hiding places. Today I am looking for starfish or sea stars. It takes me a while to find one, but finally I do. The one I find is called a brittle star. Brittle stars trap small soft-bodied creatures with the small, yet sharp, spines on their arms. When an arm is pulled off, a new arm grows in its place or from the broken end.A brittle star's mouth is on the underside of its body. In order to move, brittle stars wiggle their arms from side to side. A brittle star's spines are part of its skeleton. They belong to a group of animals called Echinodermata, which means, "spiny skinned." As I keep looking, I find five more brittle stars clinging to the rocks. Next week I am planning to return and observe barnacles, urchins, and chitons.

 

September 28, 2000
It is 12:50 in the afternoon and today I am focusing on chitons, barnacles, and urchins. I start out by searching the rocks for chitons. I find one clinging to a rock. Chitons are about half an inch long and use raspy files on their feet to scrape off algae from the rocks to eat. They have eight sections that let them cling to uneven rocks. Chitons usually eat at night so I wasn't able to observe them eating. These creatures do not only eat vegetation. Sometimes chitons eat worms and other small creatures. A chiton's enemies are usually sea stars and anemones.

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Barnacles reaching for their next meal.


Next to the chiton I see a group of barnacles. Tide pool barnacles open their shells when the tide comes in and let their feather-like legs pull food into their mouths. When it is low tide, barnacles close up and stay closed until high tide. Barnacles are related to shrimp and crabs. They don't move because their shell is permanently attached to the rock.

Sea urchins, which are related to starfish, are among the most popular tide pool animals. Like starfish, they too are classified as Echinodermata. Sea urchins move around using their tube-like feet. Although sea urchins have spines, predators such as fish often attack them. To camouflage themselves, sea urchins use their tube-like feet to pull bits of seaweed onto their spines. A sea urchin's skeleton is made up of plates that grow as the animal grows. The spines of sea urchins are attached to these plates and are very sharp. If one of these spines breaks off, a new one will grow and replace it. Some spines have special pincers that contain poison. These pincers will break off and inject poison into the attacker's skin. I plan to visit one more time next week and observe limpets and the striped shore crabs that live at Doheny Beach.

Doheny tide pool at low tide


October 8, 2000
The time is 5:00 pm and I am searching for limpets and the striped shore crabs that are under almost every rock. I turnover a rock and find about thirty crabs living beneath it. In a split second they find a hiding place and crawl into it.I manage to catch one and I look at it for a long time. Crabs are very interesting creatures. Most crabs are both hunters and scavengers. Crabs usually have two pincers, which they use to catch food with. Most species of crabs spend most of the day hidden under or between rocks.

I see a limpet attached to the rock I turned over. I try to pull it off but it won't budge. Limpets are a type of snail.They eat algae that they scrape off of the rock to which they are attached. After a limpet is finished eating, it returns to its special place on the rock. A limpet's shell fits very tightly against the rock and is almost impossible to remove. The sun is going down and it is time for me to leave.

My expedition has come to an end, but it has been incredibly interesting. I have learned and discovered a lot about tide pools and plan to further my research about tide pools by learning about how to protect tide pools and the endangered animals in them.

 

References

Barnhart, Diane. Tidepools. Parsippany, New Jersey: Silver Burdett Press, 1995.

Bendick, Jeanne. Exploring an Ocean Tide Pool. New York: Henry Holt and Company Inc., 1992.

Carson, Rachel. The Edge of the Sea. Boston: Houghton Mifflin Company, 1955.

Fleisher, Paul. Tide Pool. Tarrytown, New York: Marshall Cavendish Corporation, 1998.

Greenaway, Frank. Tide Pool. New York: Dorling Kindersley Inc., 1992.

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