1. Seaweeds
The Multicellular
Marine Algae

2. Seaweeds or Macroalgae are the large primary producers of the sea.
Though more complex than the unicellular algae, seaweeds still lack the complex structures found in land plants.

3. General Structure

4. This is a very diverse group, and although they lack true leaves, stems, and roots, they have a few common structures.

5. The complete body is called the thallus no matter the growth form.
Usually, all regions of the thallus can photosynthesize.

6. The leaf-like flattened portions are called blades.
The blades are usually the main photosynthetic region.These are not true leaves because they lack veins.

7. Most seaweeds have gas-filled bladders or floats that will help them maximize sunlight exposure. Sometime these floats contain carbon monoxide.

8. Some seaweeds have a stem-like structure called the stipe
Some seaweeds have a stem-like structure called the stipe. This structure is not found on all seaweeds.

9. The stipe also allows a place for the attachment of the blades.
The stipe provides support and can be long and tough, as in the Giant Kelp.
The stipe also allows a place for the attachment of the blades.

10. A holdfast is a root-like structure that holds the seaweed to the bottom. This structure does not aid in gathering nutrients.

11. The holdfast does not penetrate through sand or mud, so like this Sea Palm, most macroalgae are only found on hard sediments.

12. Types of Macroalgae

13. The are three types of macroalgae
Green
and
Red
Brown

14. Green Algae
About 700 of the 7,000 species of green algae are marine. Of those, few are multicellular.

15. Green Algae
Green algae can be very common where the salinities vary a lot ( Bays, Estuaries, Tide Pools)

16. Green Algae
They are usually bright green because the chlorophyll is not masked by other pigments.

17. Green Algae
Green algae have a simple thallus when compared to red and brown algae.

18. Many forms are filamentous or form paper-thin sheets.
Green Algae
Many forms are filamentous or form paper-thin sheets.

19. Others form spongy fingers as in this example of Dead Man’s Fingers.
Green Algae
Others form spongy fingers as in this example of Dead Man’s Fingers.

20. Brown Algae
Almost all species of brown algae are marine. The best known and the most complex are the kelps.

21. Brown Algae
Color varies from olive green to dark brown because there are many yellow-brown pigments that mask the color of chlorophyll.

22. Biology of Seaweeds – Brown Algae
Division Phaeophyta (=Fucophyta) - Brown algae
Photosynthetic pigments: Chlorophyll a, c ; Carotenioids (including
fucoxanthin which give the brown coloration)
Major storage products: Laminarin, oil
Major cell wall component: Cellulose
Brown algae are extremely common off the coast of California; here are some examples:

23. Brown Algae
Besides the well known kelps, Sargasso weed is also a well known brown algae.

24. Brown Algae
Sargasso weed often forms into large mats in the mid Atlantic where unique animals and communities can be found.

25. Can you see the Sargassum Angler Fish?
Brown Algae
Notice anything here?
Can you see the Sargassum Angler Fish?

26. There are more species of marine red algae than green or brown.
Most are actually red!

27. Biology of Seaweeds – Red Algae
Division Rhodophyta – Red algae
Photosynthetic pigments: Chlorophyll a; Phycobilins [including
phycoerythrin (red in color) and phycocyanin
(blue in color)]
Major storage products: Starch
Major cell wall component: Cellulose, Agar, Carrageenan
and in case of coralline algae, Carbonates
Some examples of red algae from the California coast:

28. Red Algae
Some red algae have calcium carbonate within their cell walls.
These, help form coral reefs.

29. Photosyntesis – Pigments
The first step of photosynthesis involves using pigments to capture light.
The range of visible light used for
photosynthesis is from about
400 to 750 nanometer wavelengths
of electromagnetic radiation…
this range is referred to as PAR –
Photosynthetically Active Radiation.
Although chlorophyll is the primary
pigment used by plants (it’s what makes
plants green…), other pigments such as
carotenoids and phycocyanin are also
used… why do you think this is? Why
may this be of particular interest in
algal systems?

30. Alternation of Generation

31. …You eat seaweed even if you have never tried these exotic dishes…..
Seaweeds are in a lot of products in a typical US
grocery store; They are included in things you use
everyday, like toothpaste as well as treats like ice
cream and yogurt.

32. How about a quick quiz?
The entire body of the seaweed is called the _____.
What is another name for seaweeds?
Name the 3 types of seaweeds.

33. 4. What is the stem-like structure called?
5. Which type of seaweed can be important in the formation of a coral reef?

34. Answers
Thallus
Macroalgae
Red, Green, and Brown
Stipe
5. Red