Seaweeds The Multicellular Marine Algae

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.

General Structure

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

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

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.

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

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.

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.

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

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

Types of Macroalgae

The are three types of macroalgae Green and Red Brown

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

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

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

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

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

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.

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

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

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:

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

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

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

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

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:

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

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?

Alternation of Generation

…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.

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.

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

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