Lesson Overview Lesson Overview The Ecology of Protists Lesson Overview 21.3 The Ecology of Protists

Lesson Overview Lesson Overview The Ecology of Protists Diversity Photosynthetic protists include many phytoplankton species and the red and brown algae, as well as euglenas and dinoflagellates. These organisms share an autotrophic lifestyle, marked by the ability to use the energy from light to make a carbohydrate food source.

Lesson Overview Lesson Overview The Ecology of Protists Feeding Fish and Whales Photosynthetic protists make up a large portion of phytoplankton, the small, free-floating photosynthetic organisms found near the surface of oceans and lakes. About half of Earth’s photosynthesis is carried out by phytoplankton.

Lesson Overview Lesson Overview The Ecology of Protists Supporting Coral Reefs Coral reefs, which are found in warm ocean waters throughout the world, provide food and shelter to large numbers of fish and other organisms. Protist algae known as zooxanthellae provide most of the coral's energy needs by photosynthesis. By nourishing coral animals, these algae help maintain the equilibrium of the coral ecosystem. Coralline red algae also help to provide calcium carbonate to stabilize growing coral reefs.

Lesson Overview Lesson Overview The Ecology of Protists Providing Shelter The largest known protist is giant kelp, a brown alga that can grow to more than 60 meters in length. Kelp forests provide shelter for many marine species. Kelp is also a source of food for sea urchins.

Lesson Overview Lesson Overview The Ecology of Protists Recycling Wastes Many protists grow rapidly in regions where sewage is discharged, where they play a vital role in recycling waste materials. When the amount of waste is excessive, however, populations of protists like Euglena can grow to enormous numbers and create an algal bloom, which can disrupt ecosystem homeostasis.

Lesson Overview Lesson Overview The Ecology of Protists Recycling Wastes An algal bloom in a pond or lake can deplete nutrients from the water, and the decomposition of the dead protists can rob water of its oxygen, causing fish and invertebrates to die. Algal blooms of marine protists called dinoflagellates create what is known as a red tide. The buildup of toxins produced by these protists can poison fish and shellfish.

Lesson Overview Lesson Overview The Ecology of Protists Heterotrophic Protists How do heterotrophic protists obtain food? Some heterotrophic protists engulf and digest their food, while others live by absorbing molecules from the environment.

Lesson Overview Lesson Overview The Ecology of Protists Amoebas Amoebas can capture and digest their food, surrounding a cell or particle and then taking it inside themselves to form a food vacuole. A food vacuole is a small cavity in the cytoplasm that temporarily stores food. Once inside the cell, the material is digested and the nutrients are passed along to the rest of the cell. Indigestible waste materials remain inside the vacuole until the vacuole releases them outside the cell.

Lesson Overview Lesson Overview The Ecology of Protists Ciliates Paramecium and other ciliates use their cilia to sweep food particles into the gullet, an indentation in one side of the organism. The particles are trapped in the gullet and forced into food vacuoles that form at its base.

Lesson Overview Lesson Overview The Ecology of Protists Slime Molds A slime mold is a heterotrophic protist that thrives on decaying organic matter. Slime molds are found in places that are damp and rich in organic matter—on the floor of a forest or a backyard compost pile, for example. Slime molds play key roles in recycling nutrients in an ecosystem.

Lesson Overview Lesson Overview The Ecology of Protists Protists That Absorb Some protists survive by absorbing molecules that other organisms have released to the environment. Water molds, for example, grow on dead or decaying plants and animals, absorbing food molecules through their cellulose cell walls and cell membranes. This dead goldfish is covered with the common water mold Saprolegnia.

Lesson Overview Lesson Overview The Ecology of Protists Mutualists Many protists are involved in mutualistic symbioses, in which they and their hosts both benefit. For example, red algae maintain a mutualistic relationship with the animals of the coral reef, which could not survive without the protists’ help.

Lesson Overview Lesson Overview The Ecology of Protists Intestinal Diseases Water-borne protists are found in streams, lakes, and oceans. Water supplies contaminated by animal or human feces can spread protist parasites, causing serious and sometimes deadly outbreaks of intestinal disease.