Marine Algae and Plants


Algae: Kingdom Protista

Photosynthetic, plant-like

Vary in size: microscopic (unicellular) to macroscopic


Important primary producers in marine environments

Microscopic Algae

Mulitcellular Algae

Macroalgae Structure

Thallus: simple body structure of algae




Typically has three parts

Holdfast: root-like, anchors algae to substrate

Stipe: stem-like; hold up blades, absorbs shock of waves,

Blades: leaf-like; site of sexual reproduction

Gas bladders

(pneumatocyst): gas filled floats used in flotation

Phylum Chlorophyta

Also known as Green Algae

Can be unicellular or multicellular

Live in terrestrial, freshwater and marine environments

Contain chlorophyll a and b as the main pigment

It is believed that plants evolved from green algae.

Calcareous algae play an important role in the formation of coral reefs.

Green Algae

Phylum Phaeophyta

Also known as Brown Algae


Vary from olive green to dark brown

Contains the pigment Fucoxanthin (yellow-brown) in addition to chlorophyll a and c

Contains the algae known as Kelp

Brown Algae


Most complex and largest of all brown algae

Areas with high density of kelp are called kelp forests or kelp beds.

Most are found in cold, nutrient rich, shallow waters

Mainly found on coastlines where upwellings occur.


Found in warm water

Small, spherical air bladders to keep seaweed floating at the surface.

Many organisms live in sargassum and are found no where else.

Provides food and shelter for baby sea turtles.

Sargasso Sea: North Atlantic

Phylum Rhodophyta

Also known as Red Algae

More species than green and brown algae combined

Contain pigments known as phycobilins (phycocyanin and phycoerythrin) and chlorophyll a

Coraline algae are important in coral reef formation

Red Algae

Algae Reproductive Cycle

Leafy part of the algae is the thallus

The diploid sporophyte thallus produces spores


Spores have flagella and swim away, once they reach a suitable substrate they develop into a haploid gametophyte thallus.

The gametophyte thallus produces gametes

(sperm and egg cells)

Two gametes fuse to produce a zygote and develop into the next leafy diploid sporophyte

Alternation of Generation

Reproductive cycle with the succession of two types of generations: sporophyte generation-asexual and gametophyte generation- sexual

Found in some land plants as well.

Alternation of Generation

Importance of Algae

Phycocolloids: gelatinous chemicals used in food processing

-algin: stabilizer and emulsifier in dairy, processed foods, shampoo, shaving cream, plastics, pesticides, etc….

-carrageenan: emulsifier; gives body to dairy and processed foods

-agar: form jellies

Kingdom Plantae

Flowering Plants: A.K.A. Angiosperms

Phylum Magnoliophyta

Dominate the land only a few in the ocean.

Only seagrasses are truly marine


Not grasses but members of the lily family

Completely submerged, found in shallow subtidal zones

Create hiding places for other organisms

Underground stems (rhizomes) help stabilize sandy ocean floor

Flower underwater and disperse pollen in thread under water

60 species





Marsh Grass

Grow along the sandy beaches, never completely submerged by water

Halophytes: contain salt glands which help them excrete excess salt.

Provide habitat for crabs and mussels

Help break down industrial pollutants that flow into marshes

Marsh Grass


Trees and shrubs adapted to live along tropical and subtropical shores

Important producers

Offer protection for young organisms

Over 80 different species


Mangrove Adaptations

Coping with salt:

 filtering out as much as 90 percent of the salt found in seawater as it enters their roots.

Some species excrete salt through glands in their leaves.

 concentrate salt in older leaves or bark, when the leaves drop or the bark sheds, the stored salt goes with them.

Hoard fresh water:

Like desert plants, mangroves store fresh water in thick succulent leaves.

A waxy coating on the leaves of some mangrove species seals in water and minimizes evaporation.

Small hairs on the leaves of other species deflect wind and sunlight, which reduces water loss through the tiny openings where gases enter and exit during photosynthesis..

Breathe in a variety of ways:

Some mangroves grow pencil-like roots that stick up out of the dense, wet ground like snorkels. These breathing tubes, called pneumatophores, allow mangroves to cope with daily flooding by the tides.

Pneumatophores take in oxygen from the air unless they're clogged or submerged for too long.