Chapter 6
Seaweeds and
Plants
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Seaweeds and plants:
1.multicellular
2.primary producers
photosynthesis
3.important as source of:
chemical energy
oxygen
4.eukaryotes
Primary producers : organisms that manufacture organic matter from
CO2
• Seaweeds:
– Macrophytes or macroalgae
– Classification based on:
•Structure
•Types of pigment
•Food products they store
– All seaweeds are algae, but all algae aren’t
seaweeds!
•Seaweeds are not plants!
– Plants have a vascular system
•Tissues for transporting water, nutrients and
the products of photosynthesis
•A reproductive system with flowers
•True leaves, stem and roots
Fig. 6.1
General
structure
Thallus
Complete
body
General Structure of seaweeds
• Thallus
– The complete body
– filament, thin leafy sheet, or giant kelp
– Water and nutrients picked up across the
surface
• Holdfast
– Root like attaches thallus to the sea bottom
– Not for absorption, can’t penetrate sand or
mud
• Stipe
– Stemlike structure for support
– Pneumatocysts
•Gas filled bladders
•Keep blades close to surface
• Blades
– Leaflike flattened portions
– Large surface area
– Site of photosynthesis
• Not true leaves: no veins, upper and lower surfaces the same
• 3 types of algae
Green, brown and red algae
• Green algae – Phylum Chlorophyta
– Freshwater, terrestrial and marine
• About 10% of 7,000 species are marine
– Simple thallus
• May be filamentous (branched or unbranched)
• May form sheets (Ulva)
– Pigments and food reserves like land plants
• Pigments: chlorophyll a, b and carotenoids
• Color not masked by other pigments (bright green!)
• Stores food as starch.
Fig. 6.2
Ulva, or sea
lettuce,
Green algae,
common on rocks
where fresh water
meets the sea.
Fig. 6.3
Dead man’s
fingers
(Codium fragile)
Forms branched clumps
on rocky shores
Chloroplasts remain alive
and photosynthesize in
sea slugs that feed on
the seaweed
• Calcareous green algae
– Thallus of numerous segments
– Deposits calcium carbonate
– Plays a role in the formation of coral reefs
• Brown Algae – Phylum Phaeophyta
– Colors from olive green to dark brown
– Yellow brown pigments + chlorophyll
• Fucoxanthin
– 1500 marine species
– Dominant primary producers on temperate and polar
rocky coasts
– Largest seaweeds
– Structurally most complex seaweeds
Fucus
Rockweed,
or wrack,
In Atlantic
and Pacific
temperate
waters
• Sargassum (sargasso weed)
– In warm waters
• Gulf of Mexico
• California
• Sargasso Sea (north of West Indies)
• Natural absorbent for heavy metals
– Used to clean industrial waste
Fig. 6.4
Padina, a brown algae,
produces clusters of flat
bladfes that are rolled into
circles.
Fig. 6.5
Spiral rockweed,
common on rocky
shores of the Atlantic
coast
Fig. 6.6
Knotted rockweed
North America and
European coasts of the
North Atlantic
Brown
algae!
Fig. 6.7
Seapalm, a brown algae, a
species of kelp, common to
rocky shores with heavy wave
action
Pacific Coast of North
America
Fig. 6.8
Giant kelp:
Macrocystic
pyrifera
• Kelp -largest and most complex brown algae
•
•
•
•
Grow below tide level
Temperate and subpolar latitudes
Provide food and shelter for many organisms
May be a single blade (Laminaria)
– Harvested for food
• May be ribbed (Alaria)
– Up to 25 m long (82 ft)
• Largest Pacific kelps grow just below lowest tide level
– Bullkelp (Nereocystis)
– Macrocystis – largest
• Form kelp beds or forests (Monterey Bay Aquarium)
• Harvested by chopping off the tops
• Red Algae
– Phylum/division: Rhodophyta
– Red pigments mask chlorophyll
• Phycobilin
–
–
–
–
Shallow-water marine environments
Harvested for food
Most are filamentous
Some are heterotrophic
Fig. 6.9
Porphyra, a red algae,
Inhabits temperate, polar, and
tropical rocky shores.
Fig. 6.10
Coralline red algae deposits calcium carbonate in their cell walls.
May be encrusting on rocks - help develop coral reefs.
Reproduction in Algae
Asexual
• Fragments of the thallus
can grow into new
individuals
– Sargassum
Sexual
• Meiosis
– Produces (1n) gametes
• Gametes from two
individuals fuse
– Makes unique genetic
combinations
• Male and female gametes
can form on the same
thallus
SPORES
• Specialized cells
– Dispersing to new locations
• Some have flagella - zoospores
– Protection through unfavorable conditions
– A diploid, spore-producing generation is called a
sporophyte.
– A haploid, gamete-producing generation is called a
gametophyte.
Fig. 6.11
C
C
Only one
thallus and it
is diploid .
Fig. 6.12
Fig. 6.13
Fig. 6.14
Fig. 6.15
Page 111
Harvesting kelp in Japan
TABLES
Tab. 6.1