Beacon Lesson Plan Library

Barnacles: Harder than Cement

summer zephyr
Bay District Schools


Students will be fascinated watching the movements of the complex animal hidden inside the tiny barnacle shells. This lesson allows students to study the behavior, adaptation, and larval stage of the barnacle.


The student knows that body structures are uniquely designed and adapted for their function.

The student understands the mechanisms of asexual and sexual reproduction and knows the different genetic advantages and disadvantages of asexual and sexual reproduction.

The student knows that investigations are conducted to explore new phenomena, to check on previous results, to test how well a theory predicts, and to compare different theories.


Part 1
For each student or pair of students:
-1 Clump of live barnacles (three or four)
-1 Small bowl
-1 Thermometer
-Watch or timer or clock with a second hand
-Cool saltwater or ice in large dishes to form an ice bath
-Warm saltwater
--Barnacles- student activity pages
NOTE: the cool and warm water should have a temperature difference .

Part 2
For each student or pair of students:
-Small bowls
-Dissecting microscope
-Live plankton or brine shrimp or fine fish food
-Eye dropper (or a stirring rod if using fish food)
-food coloring
--Barnacles- student pages

Part 3
For each student or pair of students:
-1 Clump of live barnacles
-Cmall bowl
-Fine mesh nylon cloth or plankton net
-Dissecting or compound microscope
--Barnacles- student pages


Step 1 Pre- preparation Aquisition of Barnacles

-Barnacles- requires living barnacles, either collected from a local beach or purchased from a scientific supply company.
1. Please check the laws governing collection of barnacles and other invertebrates before collecting. Many states require permits, most often available from the State Department of Fisheries. It is probably easiest to collect shells or rocks with their attached barnacles.Look on pilings or under boats. You may ask a scuba diver to collect them for you. Collected in this way, they can also be returned alive.
2. Barnacles may be maintained in a saltwater aquarium with relative ease. You can even keep them in a refrigerator if you aerate them periodically with an air pump or by blowing into their water with a straw.
3. The lab is divided into three sections, which may be performed on successive days, if desired. In the third investigation, a plankton net or fine mesh nylon cloth may be used to collect the larval stages of barnacles. A local plankton shore seigning, especially one done during spring, summer or fall, may contain ample larvae. Or this section may be eliminated from the lab without affecting the effectivenes of the lab.

Step 2 Background needed by teacher:
Barnacles are one of the most common rocky shore intertidal marine animals. There are species of barnacles living in all intertidal zones, some are subtidal and some even live on whales. Some barnacles are parasitic and look so different from their free-living barnacle relatives that they were only found to be barnacles because of the presence of a typical barnacle cypris larva stage. But perhaps the most amazing barnacles are those that live in the upper intertidal zones, submerged only for a short time during each tidal cycle. Their endurance is remarkable.
Their adaptations for intertidal life also make them excellent laboratory animals. With just a little care, they can survive some handling in the laboratory and some manipulation of environmental conditions.
Barnacles also make an excellent animal for experimentation because their behavior of moving their cirri through the water is easy to count and changes when environmental conditions change. At the same time, different barnacles can have different behaviors and one barnacle's behavior can change unpredictably. This makes them varied enough to stay interesting. Students will be fascinated watching the movements of the complex animal hidden inside the tiny barnacle shells.

Step 3 Set up labs according to information found under -Materials-.


Step 1 Knowledge: Cover this with students before beginning lab experiementation.

Important concepts to be covered:
1. Many species of barnacles live in intertidal areas and are particularly well adapted to endure the stresses of long exposure at low tide.

2. Barnacles extend their cirri and move them through the water to absorb oxygen and collect food.

3. Cirri movements vary with environmental changes.

4. Barnacles are hemaphroditic, reproduce sexually and go through planktonic larval stages before attaching to hard substrates.

-Key Words-
-adaptation - hereditary characteristic of an organism in a population that improves its chances for survival
-calcareous - of, containing, or like calcium carbonate
-cirri - slender appendages serving as feet
-Crustacea - group of arthropod animals (class) possessing a hard shell and including lobsters, crabs, and barnacles
-cyprid stage - developmental stage of barnacles characterized by six legs, large antennae, and cement glands
-hermaphroditic - characterized by the presence of the reproductive organs of both sexes
-nauplius stage - developmental stage of barnacles beginning at about 10 days after fertilization during which the larvae are free swimming; precursor to cyprid stage
-substrate - the base on which a sessile (nonmotile) organism lives or grows
-taxonomists - scientists who describe, identify, name, and classify organisms
-zooplankton - animal plankton

Step 2 Lab experience:
Students are paired.
Each student receives his own student copy of the activity sheet.
Each student hands to teacher his own completed lab activity sheet at end of activity.
Teacher circulates through the class as the investigations are being performed.

Step 3 Assessment
Upon completion of the investigations, plan to provide time for a discussion of the results and techniques, as well as to provide answers to the questions.
Allow plenty of time to discuss the experiments, probably on the fourth day.

Answer Key to Student Activity sheet
Part 1

1. Answers will vary. Accept students' hypotheses about what the barnacles are doing as they move.

2. Answers will vary. Accept student predictions about how barnacle movements will vary with water temperature.

3. d. The answer will depend on experimental results. In general, barnacles are more active in warm water. They will slow and stop in water above 25 or 30 C.
Analysis and Interpretation Experimental results will vary.

4. Accept student ideas. You may want to share with students that cold water tends to hold more oxygen than warm water. Barnacles may move more in warm water because they are working harder to get oxygen. In addition, barnacles warm as the temperature of their environment warms, increasing their metabolism and speeding up their activity.

Part 2
1.The opening of an acorn barnacle is covered by two pairs, or four, shell plates.

2. Student descriptions of changes in barnacle movements will vary. The barnacles may speed up or slow down. They may extend more or less completely. They may wave their cirri from side to side instead of opening and closing.

3. Answer depends on experimental results. In general, barnacles either continue to extend and retract their cirri but at a faster rate when food is present in order to catch more food, or they hold their cirri open for a long time allowing food to accumulate. This latter behavior will result in lower cirri counts.

4. Student responses will vary. See explanations for cirri movements in answer #8 above.

5. Answers will depend on what students observe. Cirri usually create a definite water current.
Analysis and Interpretation

6. A receding tide or the threat of a predator would cause a barnacle to close its shell plates.

7. Answers will vary depending on the behaviors students observed.

8. Barnacles feed by setting up a current with their cirri that brings plankton to them. The cirri then trap the plankton and pull it into the barnacle shell to the barnacle's mouth.

Part 3
Barnacle Life Cycle

9. The distribution of barnacles is accomplished during the larval stages. The free-floating larvae effectively spread the barnacle population.

10. There are several possible advantages to the crowding seen in adult barnacles. The crowding may serve to trap water and reduce the effects of drying for intertidal species. Crowding facilitates reproduction. Dense aggregations also increase the likelihood of cross-fertilization. It is also possible that the combined beating of numerous cirri may serve to create more substantial currents and move more food and oxygen past the barnacles. Your students will probably have other hypotheses.

11. The most obvious adaptation that helps prevent drying is the moveable shell plates, which may be tightly closed. In addition, the impervious shell also resists drying. The barnacle also traps a small amount of water inside when it closes, thereby reducing the effect of any drying by providing additional moisture. Many of the structures and behaviors observed in studying the barnacle relate to protection from desiccation.

12. Students come to their own conclusions. Did they really get it.....The whole purpose of the lab activity?


Upon completion of the investigations, plan to provide time for a discussion of the results and techniques, as well as to provide answers to the questions.
Allow plenty of time to discuss the experiments, probably on the fourth day. Questions (found in the associated file) should be answered with accuracy and understanding. Students who are having problems should be paired with those who aren't or should meet individually with the teacher.


Students could do a KWL chart prior to the lesson and then complete it on the fourth day, making the point that the information was obtained through investigation and observation.

Web Links

Web supplement for Barnacles: Harder than Cement

Attached Files

Student Activity Scheet     File Extension: pdf

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