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. 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. 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 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. 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. 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 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. 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. 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

There are three types of macroalgae Green Brown and Red

Green Algae About 700 of the 7,000 species of green algae are marine. Of those, few are multicellular. 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 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. 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 have a simple thallus when compared to red and brown algae.

Green Algae  Phylum – Chlorophyta  Attach to rocky substrates on or near the surface  Primary pigment is chlorophyll

Green Algae  Enteromorpha –Filamentous –Thrives in diverse environmental conditions of the upper intertidal zone  Winter/summer  High/low tide (wet/dry) Enteromorpha compressa

Green Algae  Acetabularia –Subtidal zone –Resemble a miniature umbrella –One large single cell 8cm long –Found in the warm waters of the Gulf of Mexico and off the Florida Coast Acetabularia ryukyuensis

Green Algae  Codium –Subtidal zone –Spongy, with branching structure –Codium magma grows to 6 meters in length –Codium fragile grows to 1m –Attaches to rocks or shells Codium tomentosum

Brown Algae Phylum Phaeophyta Brown or olive green color Pigments chlorophyll and xanthophyll Provide shelter or nutrients for marine organisms

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

Brown Algae  Fucus “rockweed” –Attaches to rocks in intertidal zone –Atlantic, Pacific, and Gulf Coasts –Anchors with a holdfast to rocks –Air filled bladders in some species, which hold fucus upright to absorb more light

Brown Algae  Laminaria –Kelp –Lives in the colder waters of the temperate zone  Coasts of ME and CA –Subtidal zone –Large, sturdy holdfast –Giant Kelp: Macrocystis and Nereocystis grow to >60m –Form forests that are home to fish, shellfish, sea urchins, sea lions, sea otters, and sharks

Brown Algae  Kelp produces algin –Used in prepared foods, medicines, paints, and paper products

Brown Algae  Sargassum –Floats on surface or attached –South Atlantic Ocean and off the coast of Asia –Form floating mats –Sargasso Sea –Support fish, shellfish, young sea turtles that are protected by the mats

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

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

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

Red Algae  Phylum Rhodophyta  Intertidal to Subtidal Zone  Pigments: –Red (phycoerythrin) – Blue (phycocyanin) –Green (chlorophyll) masked

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

Red Algae  Porphyra (Nori) –Attached to rocks in the lower intertidal zone –Eaten for food

Red Algae  Chondrus crispus –Short, bushy seaweed found in the lower intertidal and subtidal zone –“Irish Moss” –Carpets rocks with a dense, spongy growth –Contains carageenan, used in ice cream, pudding, and toothpaste

Red Algae  Corraline Seaweed –Corralina –Calcium carbonate in cell walls –Hard and brittle –Attached to rocks in the lower intertidal zone from Canada to Long Island

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?