1. Seaweed Structure and Function
2. Seaweed Classification
3. Seaweed Adaptations
4. Plants in the Sea
5. Problems Plants Face in the Sea
6. Plant-Dominated Marine Habitats

Seaweeds are Successful Marine Organisms

1. Primarily marine organisms
2. Seaweeds evolved in the sea.

Seaweeds are Important Autotrophs

1. Provide food and cover for animals.
2. Photosynthetic: use sunlight as an energy source to produce sugar
3. General formula for photosynthesis:

6CO₂+6H₂O -----> C₆H₁₂O₆+6O₂

Seaweeds Differ from Plants

1. Seaweeds differ from terrestrial plants
2. Although multicellular, seaweeds lack roots, stems, leaves, flowers, fruits and seeds

Lack Conducting Tissues

1. No vascular tissue for transporting food and water
2. Giant kelps are an exception

Lack Supporting Tissues

1. No wood
2. Seaweeds get support from water via buoyancy
3. Can reach large sizes without supporting tissues

Lack Specialized Absorptive Tissues

1. No root hairs and stomates
2. Get gases and minerals from water by diffusion

Simple Seaweeds

1. A simple body is called a thallus
2. A filament, mass, branched structure or encrustation

Complex Seaweeds

1. Holdfast: anchors
2. Stipe: holds blades in light and acts as a shock absorber
3. Blade (frond): exposes surface to light and nutrients in seawater
4. Air bladders: provide buoyancy

Seaweed Reproduction

1. Seaweeds reproduce sexually by gamete formation
2. Seaweeds reproduce asexually by spore formation

Alternation of Generations

1. spore former --> gamete former --> spore former

Reds (Phylum Rhodophyta)

1. 4,000 marine species
2. Contain red and green photopigments
3. Have simple structure

Browns (Phylum Phaeophyta)


 

1. 1,500 marine species
2. Contain yellow, orange and green photopigments
3. Have complex structure

 

Greens (Phylum Chlorophyta)

1. 700 marine species (6,300 freshwater)
2. Contain green photopigments
3. Have simple structure

Adaptation to Intertidal Zone

1. Heavy wave action
2. Small, tough stipes and blades
3. Strong holdfasts
4. Hydrodynamic shapes
5. Low surface to volume ratio
6. Dessication
7. Low surface to volume ratio
8. Trap water

Adaptation to Shallows (subtidal to 30 meters)

1. Less wave Action
2. Storm waves only
3. Strong holdfasts, stipes & blades
4. Decreased light intensity
5. Higher surface-to-volume ratio
6. Long stipes and large blades

Adaptation to Depths (30 to 100 meters)

1. No wave action
2. Delicate forms survive
3. Low light
4. Very high surface-to-volume ratio
5. Highly branching forms
6. Broad blades

Accessory Pigments

1. Carotenoids and phycobilins
2. Photopigments that capture light energy and pass it to chlorophyll
3. Adaptation to low light
4. Absorb blue and green light which penetrate deepest

Plants are Primarily Terrestrial Organisms

1. Vascular plants evolved on land
2. Less than 1% are marine
3. Marine species represent an invasion of the sea from the land

Invasion of the Sea

1. Adaptations to suit the very different ocean environment
2. Evolutionary adjustment of structures and physiology

Major Aspects of Plant Physiology

1. Definition: Transpiration is the circulation of fluids in plants, caused by evaporation of water at the leaves and replacement at the roots
2. Definition: Osmosis is the diffusion of water through a semipermeable membrane

Osmotic Interactions

1. Boundary layers are either impermeable, permeable, or selectively permeable
2. A solution is either isosmotic, hyperosmotic, or hyposmotic
3. Equilibrium, plasmolysis and turgor
4. Definition: Halophyte is a salt-tolerant plant

Submergence and Transpiration

1. Transpiration is not possible in a totally submerged plant
2. Most marine species must be exposed to the air for at least a little while each day, restricting them to the intertidal zone

Submergence and Pollination

1. Land plants are wind or insect pollinated
2. Pollen is an adaptation to dry environments, carrying unflagellated sperm cells to the female organs of flowers
3. Flowers of marine plants are often held above the water
4. Water currents are often used to disperse the pollen of submerged plants

Salt

1. Plant tissues are hyposmotic
2. The concentration of tissue salts is less than the concentration of salts in seawater

Dealing with Excess Salt

1. To survive in seawater, marine plants must have special methods, not found in terrestrial plants, of dealing with excess salts
2. Exclude salt with impermeable barriers
3. Excrete salt from special glands on leaves or stems
4. Wall off salt crystals within the tissues

Salt marshes

1. Salt marshes contain halophytic grasses, herbs, and shrubs
2. Halophytic grasses

A. Spartina (cordgrass) long stemmed

B. Distichilis (indian wheat) short

1. Halophytic herbs and shrubs

A. Salicornia (pickleweed) succulent

B. Atriplex (saltbush) shrub

Importance of Salt Marshes

1. Line the east and Gulf coasts of the US
2. High productivity
3. Nursery ground for marine animals

Marine Swamps

1. Marine swamps contain mangroves
2. Mangroves are tropical, halophytic trees

A. Rhizophora (Red Mangrove)

 

Mangrove Adaptations for Life in Mud

1. Mangroves live anchored in muddy sediments
2. Prop roots stabilize the tree and trap sediments
3. Pneumatophores allow roots to breathe in anaerobic muds
4. Seedlings germinate on parent plant
5. Seedlings are shaped to spear into mud or to float root tip down
6. Seedlings grow quickly to anchor in loose muds

Importance of Mangroves

1. Line 75% of tropical coastlines
2. Mangrove swamps act as nursery grounds for marine animals
3. Protect coastlines from storm waves
4. Trap sediments and create new land

Marine Meadows

1. Marine meadows contain sea grasses
2. Sea grasses (members of the lily family)

A. Thallassia (turtle grass)

Sea Grass Adaptations for Submergence

1. Many species live continuously submerged to depths of 20 meters
2. Adaptations for continuous submergence
3. Absorb nutrients with leaves as well as roots
4. Needs of all tissues met by diffussion
5. Transpiration is unneccessary
6. Submerged flowers and current-borne pollen

Importance of Sea Grasses

1. Highly productive
2. Support marine animal populations
3. Habitat for sea turtles and sea cows