Let's talk some more about phytoplankton. Did you know that they are the most plentiful plants in the Chesapeake Bay and its tributaries? In fact, one drop of water from a local stream, river, or the Bay can contain thousands of phytoplankton! Go to the World Wide Web site listed below to see real plankton in a drop of water, then use your browser's "Back" button to return to the lesson.

• Plankton in a drop of water

As we already learned, phytoplankton are important food sources for many creatures like zooplankton, oysters, and fish. However, they have another important role, as well: they produce oxygen. This oxygen is a good indicator of the quality of the water.

Unfortunately, if phytoplankton (such as algae) grow out of control, because they have too much to "eat," problems can result. Do you remember hearing in the news all of the commotion about pfiesteria in the Bay? Pfiesteria is a phytoplankton that has lived harmlessly in the Bay for thousands of years. Suddenly in the summer of 1997 this almost unknown tiny critter grew in very large numbers and was suspected of killing menhaden fish. Some people who were in the waters where millions of these phytoplankton were floating around even became sick. To learn more about the phytoplankton pfiesteria go to the Web sites listed below, then return to the lesson.

• State of the Bay - Pfiesteria

• What is Pfiesteria?
  (At this Web site you only need to take a look at the microscopic pictures of pfiesteria.)

One thing that can cause phytoplankton to grow out of control is the presence of too many nutrients. Nutrients, such as nitrogen and phosphorus, are a part of the air that we breathe, the water we drink, and the ground underneath our feet. Phytoplankton need some nutrients to live and grow, but often these days there are more nutrients in the water than is healthy. Excess amounts of nutrients get into the water from vehicle exhaust, farm field run-off, sewage treatment plants, and the rain-water run-off from housing developments and cities. The chart below demonstrates what happens under good conditions and when there are too many nutrients in the water.

Click on the image for a larger view

Nutrients act like fertilizers, causing the algae to grow out of control. This is called an "algae bloom." Eventually the algae will die and fall to the bottom. Here bacteria start the decay process and use oxygen from the water to do this. With little or no oxygen now present in the water the creatures who need this oxygen begin to get sick and die.

Click on the image for a larger view

Algae blooms can also shade the water, blocking the sunlight needed by underwater grasses to grow.

Click on the images for a larger view

To complete the next part of this lesson, you might need a copy of That Bloomin' Algae worksheet from your teacher.

With a partner or by yourself, draw your own descriptive diagram showing the effects of normal algae growth and the effects of excessive algae growth. Include a paragraph that explains your diagram.