14 Photosynthetic Stramenopiles I

Xanthophyceans, Phaeophyceans, and Their Close Relatives

Conspicuous growths of large brown seaweeds often dominate the rocky intertidal and subtidal regions of tropical, temperate, boreal, and polar oceans worldwide. Among the best known of brown algae are the giant kelps, some of which are harvested for extraction of industrially useful alginates (see Chapter 4) or for food uses. In Chile, for example, street peddlers sell the kelp Durvillaea antarctica, locally known as cochayuyo, for use in soups and other dishes. A few brown algae, transplanted from their native waters, have become notorious invasives that cause ecological damage by displacing native species. These and other brown algae, classified as Phaeophyceae, are closely related to the yellow-green algae, formally known as the Xanthophyceae or Tribophyceae. The best-known xanthophycean is the genus Vaucheria, which occurs in both freshwater and marine habitats and has a distinctive cylindrical body containing numerous disk-shaped plastids and many nuclei. As noted in Chapter 7, certain marine sea slugs puncture the cell wall of Vaucheria, suck out its plastids, and retain the plastids as photosynthetic organelles. This chapter focuses on the brown and yellow-green algae, as well as several related groups that are much less noticeable in nature.