Seaweeds and Plants
• The term seaweed refers
to the large marine algae
that grow almost
exclusively in the shallow
waters at the edge of the
world's oceans. They
provide a critical habitat
(home and food) for many
different sea animals,
lend beauty to the
underwater landscape,
and are directly valuable
to man as a food and
industrial raw material.
Structure of Seaweeds
(also called macropyhtes and macroalgae)
• thallus – the complete body
• blades- the leaf-like, flattened portions of
the thallus
• pneumatocysts- gas filled bladders which
help keep the blades near the surface
Why would blades need to be near the
surface?
• stipe- stem-like structure providing support
• holdfast- attaches the thallus to the bottom
Types of Seaweeds
•Green
•Brown
•Red
Green Algae (Chlorophyta)
• Live in freshwater,
terrestrial and marine
environments – only a
small percentage are
marine
• Typically bright green
because chlorophyll is
not masked by other
pigments
Common Green Algae
• Ulva – also known as sea lettuce
• Codium – dead man’s fingers
• Halimedia – numerous segments with
deposits of calcium carbonate – important
in the formation of reefs
• Enteromorpha – often found in polluted
areas
• Sea Lettuce
• Dead Man’s fingers
Brown Algae (Phaeophyceae)
• Almost all species are marine and the most
complex of all seaweeds
• Color varies from olive green to dark brown
• The color is a result of more yellow–brown
pigments(fucoxanthin) then chlorophyll
Common Brown Algae
• Ectocarpus – simplest brown algae which is
widely
distributed
• Dictyota –thallus is
flat and branched
Both found in the tropics
• Padina – fan- shaped
and lightly calcified
• Desmarestia – the
dominant species in
cold water – known
as Witch’s Hair
• Fucus – have gas
filled floats commonly
found on both the
Atlantic and Pacific
coasts – known as
rockweeds
• Sargassum – also
have air bladders found growing on
rocks but also found
floating in huge
masses
Particularly common in
the Gulf of Mexico
and the Sargasso
Sea
• Kelps – the most complex and largest of all the
browns. They occur in great abundance – found
below the low tide level in temperate and
subpolar latitudes, providing food and shelter.
Common Kelps
• Laminaria – made up of a single large blade –
harvested for food
• Postelsia – grows
where the waves
crash – known as sea
palm
• Nereocystis – 100 ft
long stipes – bull kelp
• Macrocystis – the largest of all the kelps, can
grow 20 inches a day and get 330 feet. Grow
close together and form kelp beds (forests)
Red Algae (Rhodophyta)
• More species of red
algae then green and
brown combined
• Red pigments called
phycobilins which
hide the chlorophyll
• Inhabit most shallow
marine environments
Common Red Algae
• Dense clumps are
common on rocky shores
exposed at low tides
• Longer- flatter
branches
predominate in areas
less exposed to air
• Chondrus – called
Irish moss – can
tolerate wide ranges
of temperature,
salinity and light and it
shape varies
depending on the
conditions
• Rhodymeniacommon in the North
Atlantic – has the
most common shape
of the red algae’s
• Coralline algae – red
algae that deposit
calcium carbonate important for reef
formation
• Variety of shapes –
thin discs, branches
with many joints,
smooth or rough
encrusting growths on
rocks
• Common variety Corallina
Life History
• Reproduction in seaweeds is by asexual
and sexual means
• Four basic types of reproduction
Most Common form
• The sporophyte produces spores by meiosis.
These spores develop into a gametophyte. Both
the spores and the resulting gametophyte are
haploid.
• The mature gametophyte produces male or
female gametes (or both) by mitosis. The fusion
of male and female gametes produces a diploid
zygote which develops into a new sporophyte.
• This cycle is known as alternation of
generations.
Carposporophyte Generation
• Very similar to sporophyte, except has a
third generation – a diploid carpospore
which develops into a sporophyte
• Still has alternation of generations
Easiest of all
• Thallus produces haploid gametes by
meiosis (both male and female) which fuse
to form diploid zygote which develops into
new thallus (brand new plant).
Last of four types
• The thallus is haploid and produces
haploid gametes.
• Fertilization occurs and forms diploid
zygote which undergoes meiosis forming
haploid spores which develop into new
thallus.
Economic Importance
Uses:
• to make paint
• as a thickener in making
shampoos, shaving
cream
• to thicken printing paste
to provide sharper
images
• to make rubber products
• making paper
• cosmetics
• found in fertilizers
• wound dressings in
hospitals
Food Uses
•
•
•
Phycocolloids – useful because they form gels at low
concentrations
Algin – used as a stabilizer and emulsifier (think dairy)
Carrageenan – used as emulsifier as well.
Flowering plants
• Seagrasses – truly marine, live below water
• Salt-marsh plants – land plants tolerant of salt
both salt – marsh plants and
mangroves live in estuaries and have only
their roots below the water
• Mangroves – trees or shrubs adapted to live
along tropical and subtropical shores around the
world
Seagrass
• Look like grass, but not
really a grass
• Stems called rhizomes
• Roots and shoots grow
from stems
• Small flowers – Why don’t
they need pretty and
large flowers?
• Very important for
providing shelter and food
Zostera – called
eelgrass
Salt – Marsh and Mangroves
• Provide habitat and
breeding ground,
protection against
erosion, and provide
a natural water
purification system.
Spartina – called cordgrass
Mangrove forest