Multicellular Primary Producers: Seaweeds and Plants

1. Multicellular Primary Producers: Seaweeds and Plants Chapter 6

2. Introduction • Nonplant photosynthetic organisms include photosynthetic bacteria and unicellular algae and the seaweeds. • The seaweeds are “plant-like” because they are multicellular primary producers. A few seaweeds are actually not primary producers but instead parasite other seaweeds.

3. Multicellular Algae: The Seaweeds Part 1of 2

4. Introduction to Multicellular Algae • Seaweeds = macrophytes = macroalgae • All multicellular (unicellular green and brown algae are not seaweeds) • Eukaryotic • There is a large variety of seaweeds

5. General Structure • Seaweeds • Lack true leaves, stem, and roots of plants • Have the following structures: • Thallus – complete body of seaweed • Blade – leaf-like flattened portion of thallus. This provides a large surface area for photosynthesis. They have no veins. • Pneumatocysts – gas-filled blades used for floatation • Stipe – stem (with no vascular tissue) • Holdfast – attaches the thallus to the bottom (not roots). No water/nutrient transport system.

6. Types of Seaweeds • There are three types of seaweed: • Green • Brown • Red • It is not always easy to rely on color for identification. Sometimes chemical analysis of pigments may be needed.

7. Types of Seaweeds • Green Algae Phylum Chlorophyta • Only about 10% of 7,000 species are marine (most of them are unicellular). • They are very common in some marine environments. • Typically they are bright green because the chlorophyll is not masked by other pigments.

8. Types of Seaweeds • Some types of green algae: • Filamentous – filaments may be branched or not • Enteromorpha – have a thin thallus form a hollow tube and are found in areas of high pollution. • Sea lettuce (Ulva) – paper-thin sheets • Valonia – forms large spheres in the tropics and subtropics • Caulerpa – single tube with multiple nuclei • Dead man’s fingers – (Codium) – multinucleated filaments woven into a spongy branching thallus. • Halimeda – calcareous green algae – thallus contains filaments that contain calcium carbonate, when it dies, it plays a role in the formation of coral reefs.

10. Codium

11. Types of Seaweed • Brown Algae Phylum: Heterokontophyta, Class: Phaeophyta • Anatomy: • Brown color comes from more fucoxanthin (yellow-brown pigment) than chlorophyll. • Almost all species are marine

12. Types of Seaweed • Brown Algae • Some examples of Phaeophyta • Kelps (Laminaria, Agarum, Alaria, Egregia, Eisenia, Nereocystis, Macrocystis) • Ectocarpus • Dictyota • Padina • Desmares • Fucus – Rockweed or wracks (exposed at low tide) • Sargassum – spherical air bladders that keep it afloat

13. Ectocarpus

14. Kelp

15. Types of Seaweeds • Red Algae Phylum: Rhodophyta • Most common of the three. • Have red pigments called phycobilins which mask chlorophyll. • Mostly marine • Not as complex as brown algae, some are parasites, others have lost their chlorophyll and become heterotrophs • Most are filamentous

16. Types of Seaweed • Red Algae • Examples: • Gelidium and Gracilaria are found worldwide • Endocladia forms wiry clumps on rocks • Gigartina – one of the most massive red algae (blades up to 2m long) • Porophyta – found on rocky shores • Rhodymenia – found in the Atlantic – blades can reach 1m long • Chondrus – Iris moss • Corallina – red algae that deposit calcium carbonate – involved in the creation of coral reefs.

17. Life History • Asexual reproduction is more important than sexual reproduction. • Some seaweeds produce spores (that can live dormant in unfavorable conditions) • Some have a thick wall • Zoospores have a flagella • Sexual reproduction (with the production of gametes) is common in seaweeds. This ensures genetic variation. • Turn your textbooks the page 107. Can someone explain the lifecycles here?

20. Economic Importance • Farming or mariculture of seaweed occurs all over the world. • Seaweeds produce several types of gelatinous chemicals called phycocolloids. • Algin (an important phycocolloid) has many uses (frosting, dairy products, shampoo, shaving cream, plastics, pesticides, etc.) It is found in kelp (Macrocystis).

21. Economic Importance • Carrageenan (another important phycocolloid) found in red algae, it is used in dairy products as well as a variety of processed foods. • Agar (another important phycocolloid) protects ham, fish, and meats during canning, in low calorie foods, and as a thickener. It is also used in research. • Some other uses for seaweeds includes fertilizers, food additives, and wound dressing in hospitals.