Chapter 6
Seaweeds and Plants
Primary Producers
 Those
that use light to perform
photosynthesis
 Are always exceptions

A few seaweeds that are not primary
producers but are parasites of other
seaweeds
Seaweeds
 AKA:
Macrophytes or Macroalgae
 Are all multicellular
 Classified/characterized based on
structure as well as types of pigments and
food products they store
Structure of seaweed


Wide range of growth forms and complexity
of structures
The complete body is known as the thallus
Can be a filament, a thin leafy sheet, or
giant kelp

The leaf-like flattened portions of
the thallus are blades


Main photosynthetic region
Note: all portions of thallus can
photosynthesize as long as they have
chlorophyll


Gas-filled bladders, pneumatocysts,
sometimes keep the blades close to the sea
surface



distinct stem-like structure called stipe



Mixture of gases includes CO
Maximizes their exposure to the sunlight
Provide support
Where blades originate from
The holdfast looks like roots and attaches the
thallus to the bottom
Do not absorb significant amounts
of water/nutrients, or penetrate
through sand/mud like tree roots

Water and nutrients are picked
 up directly through the thallus

Types of seaweed
3



Basic types
Green
Red
Brown
 Hard
to recognize groups by color in nature
because of the proportion of chlorophyll and
other pigments can vary
Green Algae
 Most
live in freshwater and terrestrial
environments

Only 10% of 7,000 species are marine
 Bays,
estuaries, isolated tide pools on rocky
coasts
 Most
have a simple thallus
 Thought that land plants evolved from
green algae

Have some pigments and food reserves

Filamentous green algae are common on
rocks in shallow water and tide pools
May be branched or unbranched
 Enteromorpha




Ulva (AKA sealettuce)



Form large spheres or spherical clusters in tropics
and subtropics
Several other green algae consist of thin
filaments or tubes (siphons) formed by a single
cell with multiple nuclei


Paper-thin sheets with varying shapes depending
on environmental factors
Polar to tropic waters
Valonia


Thin thallus in the form of a hollow tube
Sometimes flourish in polluted areas
Caulerpa, Codium (Dead man’s fingers)
Halmedia (Calcareous green alga)


Numerous segments with deposits of calcium
carbonate
Plays important role in forming coral reefs
Brown Algae

Olive green to dark brown color





Due to yellow-brown pigments (fucoxanthin)
Almost all of the approx 1500 species are
marine
Dominant primary producer on temperate
and polar rocky coasts
Include largest and most complex seaweeds
Simplest have a finely filamentous thallus

Ectocarpus
 Dictyota
have a flat and branched thallus
 Padina have a fan shaped and lightly
calcified thallus

Both tropical and subtropical
 The
thallus of most species of
Desmarestia is branched in many way

Found in cold waters
 Some
of brown algae are exposed at lowtides at the middle and upper levels of
rocky shores

Thick, leathery thalli can withstand exposure
to air
 Many

species have gas-filled floats
Rockweeds, wracks, Fucus, found in
temperate shores
 The
knotted seaweed (Ascophyllum) is
found along temperate Atlantic coasts
 In
warm waters like the Gulfs of Mexico
and California these temperate species
are replaced by sargasso weed
(Sargassum)


Has pneumatocysts
Most species grow on rocks but at least 2
float offshore in huge masses
 The
sargasso sea
https://www.youtube.com/watch?v=M91toV
0zIps

An area in the Atlantic north of the West Indies
 Seaweed

drifts in other regions of the world
Gulf of Mexico
 Kelps
are the most complex and
largest of all brown algae



Most found below low tide in temperate
and sub polar latitudes
Can provide food and shelter for many
other organisms
Some consist of a single large blade up to 3
meters in length
 Laminaria
 Blades
are harvested for food in several parts
of the world
 Several blades may grow from a single
holdfast

In some species the blade is spilt/branched

Agarum and Alaria
A

rib runs along the middle of the single blade
Postelsia
 AKA
sea palm
 Grows on intertidal rocks exposed to heavy
waves
 Occurs in thick clusters from central California
to British Columbia

2 Branched forms
 Feather-boa
kelp (Egregia)
 Southern Sea Palm (Eisenia)




Both are common on Pacific rocky shores
In the Pacific the largest kelps are found in
deeper water just below the lowest tide
level
The bull kelp (Nereocystis) has a whip-like
stipe up to 30m long with a large spherical
pneumatocyst at the upper end
Another large kelp is Pelagophycus
 Similar
to bull kelp, but has impressive antlerlike branches

Macrocyotis is the largest of the kelps
 massive
holdfast attached to hard bottoms
 Several long stipes grow from holdfast where
elongated blades develop
 At the base of each blade a pneumatocyst
eventually develops
 can grow 50 cm or more per day in optimal
conditions
 form dense and very productive kelp beds or
forests in colder waters of the N and S Pacific


Harvested by chopping off the tops for the
extraction of several natural products
Among the richest most productive environments
in marine realm
Red Algae (Phylum
Rhodophyta)
 More
species in this category than green
and brown combined
 The red color is due to pigments called
phycobilins which mask chlorophyll
 Most are red, may have different colors
depending on their daily exposure to light
 The
group is essentially marine in shallowwater environments
 Some are harvested for food and for the
extraction of various products
 The structure of the thallus of red algae
doesn’t show the wide variation in
complexity and size shown in brown algae
 Some
become greatly simplified in
structure by becoming parasites of other
seaweeds
 A few have lost all trace of chlorophyll
and have become heterotrophs
depending entirely on their host for
nutrition
 Most are filamentous

Thickness, width, and arrangement vary a
great deal
 Dense
clumps are more common on the
upper levels of rocky shores that are
exposed at low tide

Longer and flatter branches dominate in
areas less exposed to air and in deeper
water
 Shown
in species of Gelidium and Gracilaria
 Endocladia forms wiry clumps on rocky shores
from Alaska and S California
 Some
species of Gigartina have large
blades as long as 2m

Among most massive of red algae
 species
of Porphyra are common on
rocky shores above the lowest tide from
polar to tropical coasts
 The most common growth form is a thallus
with thin large blades

Rhodymenia is common in N. Atlantic
 Blades

reach 1m in length
Irish mass (chondrus) is N. Atlantic red alga
 It
can tolerate wide ranges of temperature,
salinity and light
 Shape varies greatly in response to these
physical factors

Coralline algae are red algae that deposit
calcium carbonate within cell walls


Important in several marine environments
Calcified thallus takes a variety of shapes
Thin disks growing over other seaweeds
 Branches with many joints
 Smooth or rough encrusting growths on rocks




Color varies from light to intense reddish-pink;
dead ones are white
Warm water coralline are actively involved in
formation and development of coral reefs
Others thrive in temperate and polar waters
often attaining large size
Life History
 Reproduction
is a complex affair in
seaweeds
 Asexual, or vegetative, reproduction is
common
 It may be more important than sexual
reproduction in most species
 Fragments
of the thallus can grow into
new individuals

floating masses of Sargassum of Sargasso
Sea
 Some



seaweeds produce spores
cells specialized for dispersing to new
locations or persisting through unfavorable
conditions
Some are protected by resistant cell walls
Others have flagella for movement and are
known as zoospores
 The
production of gametes is a key event
in sexual reproduction
 Gametes produced by all members of a
seaweed species may be similar in
appearance or may consist of larger nonmotile eggs and smaller sperm that can
swim by flagella



Male gametes in the red algae lack flagella
and are non-motile
They may be released in strands of slime
Male and female gametes may be formed
in the same thallus but the chances are
good that fusing gametes will be from
separate thalli
 Cells
of seaweeds, as well as humans and
clams, divide and produce identical cells
by mitosis
 Seaweeds may also produce haploid
spores or gametes by meiosis
 The existence of diploid and haploid cells
is fundamental in understanding the often
complex life histories of seaweeds

The life histories can be divided into 4 types
4 types of seaweed life history

Type 1


Most common among all three groups of
seaweeds
Involves 2 types of thalli

Diploid (2n) sporophyte generation that through
meiosis produces not gametes by haploid (1n)
spores
Except in red algae these
spores are typically motile
 They divide and develop into
the second kind of thallus

A





haploid (1n) gametophyte generation
the one that produces haploid gametes
In some species there are separate male and
female thalli
In others, both types of gametes are produced
by every thallus
The gametes are released and, with fertilization,
produce a diploid zygote that develops into the
diploid sporophyte
a life history with two generations, a sporophyte
and a gametophyte, is an example of a
phenomenon of alteration of generations


In some algae such as sea lettuce and the brown
Dictyota, the sporophyte and gametophyte are
structurally identical
On the other hand, in Kelps the large plant we see is
the sporophyte, whereas the gametophyte is minute
and barely visible
 The
second type, unique to the red algae, is
more complex, involving alternation of three
generations


The third generation a diploid carposporophyte
results from the fusion of gametes
Carpospores, diploid spores produced by the
carposporophyte, develop into sporophytes
 The
third type, is similar to that of animals
(including humans)

There is no alteration of generations

Only one thallus and is diploid


Thallus produces haploid gametes by meiosis that creates
a diploid zygote after fertilization
Some brown algae and some green algae
 The



fourth type occurs in some green algae
The dominant thallus is haploid and produces
haploid gametes
With fertilization the gametes form a diploid
zygote
It is in the zygote in which meiosis takes place
resulting in haploid spores

 There
Each spore develops into a haploid individual, the
only kind of thallus in the cycle
are many known variations of these
types of life history
Other interesting things about
seaweed:
 The
development of gametes or spores
can be influenced by the amounts of
nutrients in the water, temperature, or by
day length
 High levels of nitrogen nutrients in the
water cause the development of asexual
spores in sea lettuce

Low levels stimulate the development of
gametes instead
 Release
of gametes and spores can be
triggered by the splashing of water in an
incoming tide


 In
Also by the cycles of the moon
Or chemical messengers received from
cells of the opposite sex
some seaweeds the release of male
and female gametes is timed to take
place at about the same time
Economic Importance

Around the world, workers harvest seaweeds
to be used in many ways



Most obvious is as a food source (red and
brown algae)
Farming of seaweed, mariculture, is a big
business in China, Japan, Korea, and other
nations
Seaweed produces several types of
gelatinous chemicals, phycocolloids


Used in food processing and in manufacture of
different products
Valuable for their ability to form viscous
suspensions or gels even at low concentrations

One important phycocolloid, algin
 Used
extensively as a stabilizer and emulsifier
in manufacture of dairy products (ice cream,
cheese and toppings which need to be
smooth and not likely to separate)
Page 114 for more examples

A
major source for algin for commercial uses is
the giant kelp


West coast of temperate N America (California)
Collected by large barges with rotating blades
that cut and collect the stipes and fronds to a
depth of 1-2m below the surface

Stipes quickly grow back toward the surface
 Another

source is Laminaria
Harvested in North Atlantic

The second phycocolloid is carrageenan


Obtained from red algae (Irish moss) in N
Atlantic and Eucheuma in the tropics
Valued as an emulsifier


Gives body to dairy products and a variety of
processed foods like instant pudding
Another is agar




Extracted for its ability to form jellies
Protects ham, fish, and meats during canning
Low calorie foods (not digestible by humans)
Thickener



Other examples page 114
Biologists will use it as a medium in which to
grow bacteria and mold
Obtained from red algae
 Can
also be used for fertilizer, food
additives in animal feeds, and wound
dressings in hospitls


Coralline algae are sometimes used in
Europe to reduce the acidity of soils
Some red seaweeds are marketed as
nutritional supplements
Flowering Plants



The 250,000 species of flowering plants,
angiosperms are dominant on land but few
live in the ocean
Have true leaves, stems, and roots that are all
provided with specialized tissues to transport
water, nutrients, and food manufactured by
photosynthesis
Reproduction involves a dominant
sporophyte that features an elaborate
reproductive organ, the flower



Of all of the flowering plants, only the
seagrasses are truly marine
Often live submerged by seawater, rarely
exposed at low tide
Salt-marsh grasses and mangroves inhabit
estuaries and shores protected from the wave
action


They are not at home in the ocean and usually
only their roots are covered by water at high
tide
There are also many flowering plants adapted
to colonize coastal areas exposed to saltladen winds and occasional sea spray


Do not tolerate immersion in seawater
May be found on sand dunes or living along the
edges of salt marshes
Seagrasses
 Superficially
resemble grass but are
actually not grass at all

Closest relatives seem to be from the lily
family (showing that they evolved from land
plants)
 Have
adapted to life in the marine
environment
 Have horizontal stems called rhizomes

Commonly grow beneath the sediment
 Roots
and erect shoots grow from the
stems
 Seagrass flowers are typically very small
and inconspicuous because there is no
need to attract insects for pollination

The pollen that contains the sperm is
carried by water currents
 Often

released in strands
Tiny seeds result from successful fertilization
 Seeds
are dispersed by water currents and
perhaps in the feces of fish and other animals
that browse on the plants
 Eelgrass
is most widely distributed of the
nearly 60 species of seagrass known





Found in many temperate and tropical
regions around the world
Inhabits shallow, well-protected coastal
waters such as bays an estuaries
Has distinctively flat, ribbon like leaves
Common in oxygen-poor sediments
Thick eelgrass beds are highly productive
and provide shelter and food to a variety of
animals
 Surf
grass inhabits rocky coasts exposed to
wave action


May be exposed at low tides
Found on Pacific coast of North America
Salt-Marsh Plants

Cordgrasses are true members of the grass
family





Not really marine species, but land plants that
tolerate salt
Do not tolerate total submergence by seawater
Live in salt marshes and other soft-bottom
coastal areas in temperate regions
Highly productive and provide habitat and
breeding grounds for many species important to
fisheries
Offer protection against erosion and provide
natural water purification systems
 Inhabit
the zone above mudflats that
becomes submerged by seawater only at
high tide

Leave are always partly exposed to air
 Salt
glands in the leaves excrete excess
salt
 Other salt-tolerant plants, halophytes, are
found at higher levels on the marsh

Pickle weed
Mangroves
 Trees
and shrubs adapted to live along
tropical and subtropical shores
 Flourish along muddy or sandy shores
protected from waves
 Depending on location, there are
different adaptations that mangroves
have especially regarding water loss from
salty environments
 Red
mangrove leaves are thick to adapt
to water loss
 Some other mangroves have seeds that
germinate while still attached to the
parent tree


They develop into elongated pencil shaped
seedlings as long as 30 cm (1ft) before
falling from the parent
Successful one stick in the soft muddy
sediment or float in the water to be carried
by currents to new locations