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. This structure is not found on all seaweeds.

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 ofMacroalgae

The are three types of macroalgae

Green

Brown

and Red

Green AlgaePhylum Chlorophyta

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.

Green Algae

Many forms are filamentous or form paper-thin

sheets.

Green Algae Others form spongy fingers

as in this example of Dead Man’s

Fingers.

Brown AlgaePhylum Phaeophyta

Almost all species

of brown algae are marine. The best know 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.

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.

Brown Algae Notice anything

here?Can you see the Sargassum Angler

Fish?

Red AlgaePhylum Rhodophyta

There are more species of marine

red algae than green or brown.

Most are actually red!

Red Algae Some red algae

have calcium carbonate within their cell walls.

These, help form coral reefs.

How about a quick quiz?

1. The entire body of the seaweed is called the _____.

2. What is another name for seaweeds?

3. 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

1. Macroalgae2. Thallus3. Red, Green, and Brown4. Stipe5. Red