Prince William's Oily Mess - A Story of Recovery

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a. Read Intro | b. Learn the Organisms | c. State Predictions!
a. Observe Mearns Rock | b. Record Data
a. Plot Data | b. View Example Graph
a. Interpret Data & Write Report | b. Share What You Have Learned
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Graphing Changes in Marine Life Abundance

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STEP 1b: Learn the Organisms

Use this field guide to learn more about the organisms that you will later observe in the Mearns Rock quadrats. The photo below shows representative patches of three common marine, intertidal organisms that live on Mearns Rock: Fucus (a type of algae), barnacles and mussels.

Mouse over and Click on the drawings next to the photo or scroll down to read more about the biology of these three life forms. Later, you'll observe these organisms in the photos of the Mearns Rock quadrats, estimate their percent cover, and establish the criteria you'll use to make your observations.

barnacles mussels

barnacles mussles fucus

Once you are confident that you can recognize these organisms from a photo, you will be ready to go to the next step. Remember, you can always come back to the field guide later to brush up on your organisms!

next pageProceed to Step 1c: State Your Predictions!


Barnacles (Balanus glandula)

Barnacles are tiny crustaceans (animals related to crabs, lobsters, and shrimps) that occupy volcano-like shells. They colonize rocks, pilings, and even boats, by attaching masses of their whitish-colored shells to the substrate. The shell of B. glandula consists of a number of overlapping plates. The barnacle controls the opening at the top of the shell by moving these plates. A large B. glandula is about 1.5 cm across, with its diameter about the same as its height. In large masses, you may notice that the barnacle shell is more cylinder-shaped than volcano-shaped. (Why do you think that is?) The barnacle feeds by using six feather-like appendages, called cirri. As the cirri rapidly extend and retract through the opening at the top of the barnacle, they comb the water for microscopic food.


Fucus gardeni (rockweed)

Fucus (pronounced like mucus) is a type of brown algae that grows in the middle- to upper-intertidal zone (the higher part of the tidal flat) of cold ocean waters. The body of the alga is composed of flattened "branches," some of which end in swollen receptacles that house reproductive parts (eggs and sperm). (Fucus is sometimes called "popweed." Can you guess why?) The holdfast, at the base of the alga, attaches it to the rocks on which it lives. Because Fucus is sometimes out of water for hours at a time when the tide is low, it has a thick "skin" that helps it keep its moisture, and it makes a sticky substance to keep from losing water. In late spring and summer, in locations where Fucus grows well, it may nearly cover all other intertidal organisms!


Mussels (Mytilus trossulus, the Pacific blue mussel)

Mussels are bivalves (their bodies are enclosed by two shells, or valves) that can be found firmly attached to rocks, floats, and pilings. A mussel stays attached to the substrate by its byssus, a collection of tough, leathery threads of organic material secreted by the mussel. Adult M. trossulus range from 3 to 10 cm in length and can vary considerably in color. Generally, the shell is dark blue-black or brownish black, but the shell of young mussels is often brown. Like many other bivalves, mussels are filter feeders, pulling water into their body chambers with their inhalent, or intake, siphon (the larger, frayed-edge gape on the upper edge of the mussel), and then forcing it out the exhalant, or exhaust, siphon (which is smaller and has a smooth edge). Dense masses formed by mussels provide protection and other biological necessities for many organisms, such as small shrimp, amphipods, and polychaete worms. Mussel beds also serve as a substrate to which barnacles may become attached.


Kozloff, Eugene N. 1973. Seashore Life of Puget Sound, the Strait of Georgia, and the San Juan Archipelago. Seattle, WA: University of Washington Press. 282 pp.


Glossary Express

Intertidal—on a beach, the area between high tide and low tide.

Percent Cover—the proportion (in percent) of a certain species or group of species that is occupying a surface such as the ground, a rock, etc.

Quadrat—a small plot or sample of land that is representative of the particular habitat that is being studied. Often the plot of land is demarcated using a frame made of PVC pipe or other material.


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barnacles mussles fucus