Phaeophyceae

The Phaeophyceae, commonly known as brown algae, are a large and diverse class of multicellular algae, comprising about 1,800 species. These algae are distinguished by their characteristic brown or olive-green color, a feature attributed to the presence of fucoxanthin, a yellow-brown pigment that masks the green chlorophyll. Brown algae are predominantly marine and play a vital role in coastal ecosystems worldwide.

Turbinweed Algae – Turbinaria ornata

Thalassiophyllum clathrus

Yellow Scroll Coral – Turbinaria reniformis

Turbinaria decurrens

Turbinaria conoides

Characteristics

Phaeophyceae exhibit a range of morphological forms, from microscopic filaments to macroscopic seaweeds. Some defining characteristics include:

  • Multicellularity: All brown algae are multicellular organisms, with complex tissues and structures.
  • Algin: Brown algae contain algin, a complex carbohydrate that forms a viscous gel when dissolved in water. This substance is commercially important in various industries, including food processing, pharmaceuticals, and textiles.
  • Alternation of Generations: Brown algae typically exhibit an alternation of generations, with both haploid (gametophyte) and diploid (sporophyte) stages in their life cycle. The sporophyte generation is often more dominant and conspicuous.
  • Holdfasts: Many brown algae possess holdfasts, specialized structures that anchor them to rocks or other substrates in the marine environment.
  • Blades: Brown algae typically have flat, leaf-like blades that function in photosynthesis.
  • Stipes: Some brown algae have stipes, stem-like structures that support the blades and hold them upright.

Environments

Brown algae are primarily found in marine habitats, particularly in cool, temperate waters. They thrive in intertidal zones, subtidal zones, and deeper water environments. Some species are even known to inhabit brackish waters.

Brown algae are a crucial part of marine ecosystems, serving as food sources for a variety of organisms, including herbivorous fish, invertebrates, and sea urchins. They also provide habitat and shelter for numerous marine species.

Examples

Notable examples of brown algae include:

  • Sargassum: A genus of free-floating brown algae that forms large mats in the Sargasso Sea.
  • Macrocystis: A giant kelp species that can reach lengths of over 100 feet.
  • Fucus: A genus of common intertidal brown algae, often found attached to rocks in the splash zone.
  • Laminaria: A genus of large, kelp-like brown algae that grows in subtidal environments.

References