Multicellular Algae
 Seaweeds ( macroalgae)
 Multicellular algae
Three groups of seaweeds
 Red algae – phylum(division)
Rhodophyta
 Brown algae – phylum(division)
Phaeophyta
 Green algae – phylum(division)
Chlorophyta
Rhodophyta
Irish Moss - Rich in protein and minerals
Corallines
Secrete a calcium carbonate shell that bond coral colonies together
(holds the coral reef structure together)
Nori - Rich in protein and minerals
Phylum Rhodophyta
 Red Algae
 Corallines

Secrete a calcium carbonate shell that bond coral colonies
together (holds the coral reef structure together)
 Irish Moss

Rich in protein and minerals
 Nori

Rich in protein and minerals
Phylum Rhodophyta
 Biochemistry
 Chlorophylls a, d
 Phycoerythrin (red pigments)

Allow some red algae to live much deeper than any other algae
 As deep as 200 m (656 ft)
Phylum Rhodophyta
 Ecological Roles
 Seasonal food for
herbivores, grazers
 Some form turfs and
reef sediments
 Some stabilize reef
sediments
Phylum Rhodophyta
 Commercial uses
 Agar

Used in medicine and research for culturing microorganisms
 Carrageenan



Desserts, ice cream, milk shakes, sweetened condensed milks,
puddings,
sauces: gel to increase viscosity
thickener : Shampoo and cosmetic creams….
Red Algae – Phylum Rhodophyta
 Primarily marine (98%)
 The highest diversity among seaweeds
 Mostly benthic in distribution
 Some species are epiphytes (plant living on plant)
 Coraline red algae- helps to cement loose coral
together
Important commercial uses
 Agar – culturing bacteria
 Carrageenan – thickening agent
 Source of food for human consumption, animal
feed, and used in fertilizer
Phylum Phaeophyta
 Brown Algae
 Kelp
 Sargassum
 Rockweed
Rockweed
Phylum Phaeophyta
 Biochemistry
 Chlorophylls a, c
 Pigment fucoxanthin
Phylum Phaeophyta
 Ecological Roles
 Long term food for herbivores, grazers
 very productive the Giant Kelp is the foundation for
many temperate coastal ecosystems: California, the
Mediterranean, and New Zealand
 Kelp form massive undersea forests
 Habitat for diversity of marine animals

Sea urchins, fishes, crustaceans, molluscs, sea lions, sea otters
Phaeophyta
Brown Algae – Phylum Phaeophyta
 Rockweeds, kelps, and sargassum
 Almost exclusively marine (99.7%)
 Most are benthic except for Sargassum
 Range in size from microscopic to the giant kelps
 Olive-brown color is due to pigment fucoxanthin (also
found in diatoms)
Brown Algae
 Blades of brown algae usually have gas-filled bladders
that help them to stay afloat to get maximum exposure
to sunlight
 The stipe is attached to the bottom by a holdfast
Ecological roles of Sargassum
 Sargassum forms floating mats in the North Atlantic
Ocean in an area known as the Sargasso Sea
 Habitat to a variety of organisms unique to the
sargassum
 Massive mats of sargassum support a complex and
diverse community

Several species of fish and invertebrates live only in this
ecosystem
Phylum Phaeophyta
 Commercial uses
 Brown algae is used as a food resource
 Seaweeds and algae make up 10% of the Japanese diet
 The commercial product algin is used in food
processing, salad dressing, ice cream, paint, and
abrasives

Food and chemical industries use about $250 million worth of
algin annually
Commercial products from Brown
Algae
 The alginates of some brown algae are harvested for
commercial use as thickening agents in the textile,
dental, cosmetic, and food industries
 Brown algae are used as food, and as cattle feed
Chlorophyta
Phylum Chlorophyta
 Green Algae
 Sea lettuce
Phylum Chlorophyta
 Biochemistry
 Chlorophylls a, b
 Carotenoids
 Chlorophyta share the same pigments as land plants

Evolutionarily significant, indicates that land plants
evolved from green algae
Phylum Chlorophyta
 Ecological Roles
 Seasonal food for herbivores, grazers

Manatees eat sea lettuce
 Some form turfs and reef sediments
Phylum Chlorophyta
 Commercial uses
 Can be used as a compost material and as fertilizer
Green Algae – Phylum Chlorophyta
 Contain the same types of pigments that are found in
land plants (a,b)
 Few marine species (13%), most are freshwater and
phytoplankton
Distribution of Seaweeds
 Most species of seaweed are benthic
 Fouling communities – live on pilings, bulkheads, boat
hulls...
 The environmental factors most influential in
distribution
 Light and temperature
Structure of Seaweeds
 Thallus
 The seaweed body
 Blade
 Flattened part of the thallus
 Holdfast
 Attaches the thallus to a surface
 Stipe
 Stem-like region between the holdfast and the blade
Photosynthetic pigments
 Chloroplasts in all seaweeds have chlorophyll a
 Green algae also has chlorophyll b
 Brown algae chlorophyll c
 Red algae chlorophyll d
Composition of cell walls
 Primarily composed of cellulose
 Calcareous algae may also have calcium carbonate
Reproduction in Seaweeds
 Both asexual and sexual
 Asexual
 Fragmentation

Thallus breaks into pieces and each piece grows into a new plant
 Spore formation
 Sporophyte produces spores
 Sexual
 Gametes are produced and zygote is formed

Gametophyte produces gametes
 Alternation of generations
 Asexual sporophyte and sexual gametophyte in same plant