3 Algae in Biotic Associations

Algae interact with other organisms in an amazing variety of ways, collectively known as biotic associations. For example, drifts of seaweeds that accumulate on beaches serve as food for amphipods and other terrestrial animals and also support the growth of decay microorganisms. If you take a sample of seaweed drift back to the lab and look at it with a microscope, you will see many types of small algae living on or near the seaweed. In fact, samples from diverse habitats feature algal actors involved in dramatic biotic associations. Some are voracious predators that consume their close relatives, while hungry protozoa and small animals prey on other microscopic algae. Attacked algae defend themselves by ejecting spear-like projectiles, flashing bright light, or producing foul-tasting or toxic chemicals that cause predators to reject them. The shapes and sizes of other algae make them difficult to ingest. Algae can thwart killer viruses, bacteria, or fungi with tough cell walls or by secreting coats of slimy mucilage or antibiotics. More peaceful scenes are provided by the many types of algae that live in beneficial symbiotic associations with prokaryotes, protists, fungi, animals, or plants. This chapter describes food web and symbiotic associations involving algae and their ecological, medical, and economic importance. An understanding of such biotic associations is important because human actions that disturb them can reduce global biodiversity (McCann 2007).