1. Multicellular Primary Producers: Seaweeds and Algae
Chapter 6

2. Many fascinating photosynthetic organisms populate the oceans, and for the most part, they are very different from the land plants that surround us. Most, in fact, are not considered plants at all and are therefore NOT members of the kingdom Plantae. Despite this, some biologists consider some or all seaweeds to be plants.

3. Multicellular Algae: The Seaweeds
The most familiar types of marine algae are seaweeds.
Seaweeds share a general structure, although they show a wide range of growth forms and complexity of structures:
Thallus ~ complete body
Blades ~ leaf-like, flattened portions of the thallus
Pneumatocysts ~ gas-filled bladders that keep blades close to the surface
Stipe ~ stem-like structure that provides support
Holdfast ~ structure that resembles roots, attaching the thallus to the bottom

5. Types of Seaweeds There are three types of seaweeds: Green Algae
Brown Algae
Red Algae
It is not always easy to identify the groups by their colors because nature intervenes, through proportions of chlorophyll and other pigments

6. Green Algae Belongs to Phylum Chlorophyta Common Characteristics:
Most live in freshwater
Estimated 7,000 species, only about 10% are marine
Most are unicellular
Dominate in environments with wide variation of salinity – like bays, estuaries, and isolated tide pools on rocky shorelines

7. Structure of Green Algae
Most have a simple thallus in comparison to the other two groups of seaweeds. Pigments and food reserve are same as plants, it is believed that land plants evolved from green algae Chlorophyll is not masked by other pigments, so the thallus is bright green typically

8. Examples of Green Algae
Codium – “Dead Man’s Fingers”
Caulerpa
Halimeda – Calcareous Green Alga, which means it consists of numerous segments with deposits of calcium carbonate used in formation of coral reefs

9. Brown Algae Belongs to Phylum Heterokontophyta Common Characteristics:
Color varies from olive green to dark brown due to yellow-brown pigments over chlorophyll
Approximately 1500 species – almost all marine
Dominant primary producer on temperate and polar rocky coasts
Brown algae include the most complex seaweeds
Largest of all brown algae are the kelps

10. Structure of Brown Algae
The most simple brown algae have a finely filamentous thallus that is flat and branched out Most brown algae are not considered “simple” and have a thick, leathery thallus that can stand exposure to air Many species have gas-filled bladders to keep them afloat near the surface

11. Examples of Brown Algae
Ectocarpus – simplest form of brown algae
Fucus – commonly named Rockweed
Sargassum – dominant on the California coast and the Gulf of Mexico, has spherical air bladders that keep the small blades afloat at the sea surface

12. Red Algae Belongs to Phylum Rhodophyta Common Characteristics:
More species than the marine green and brown algae combined (approximately 4,000)
Most are marine
Inhabit most of the shallow-water marine environments
Red pigments called phycobilins, which mask chlorophyll
Most species are actually red; however, some may have a different color depending on light exposure
Some harvested for food

13. Structure of Red Algae
Structure of thallus doesn’t have wide variations in complexity and size as seen in the brown algae Greatly simplified by becoming parasites of other seaweeds Few have traces of chlorophyll and have become heterotrophs, depending solely on their host for nutrients Most are filamentous, but thickness, width, and arrangement of filaments varies

14. Examples of Red Algae Gigartina– most massive red algae
Chondrus – “Irish Moss”
Corallina – red algae that deposit calcium carbonate within their cell walls. Important in formation and development of coral reefs

15. Economic Importance
Around the world, workers harvest seaweeds to be used in many ways. Mariculture (the farming of seaweed) is big business in China, Japan, Korea, and other nations throughout the world. The most obvious use is a food source as people from different cultures have discovered that many seaweeds are edible, especially some of the red and brown algae.

16. Other Economic Uses Food processing
Stabilization of dairy products – ice cream, cheese, smooth toppings (caramel, frosting), instant puddings
Shampoo, shaving cream
Pesticides
Production of paper, paints, and cosmetics
Print processing for sharper images
Canning of ham, fish, and meats
Laxatives
Fertilizer, animal feeds, reduction of soil acidity