BROWN ALGAE · OCHROPHYTA
CLASS: PHAEOPHYCEAE
Objectives
In this lab we will examine members of the Ochrophyta (Class Phaeophyceae), observing
differences in their morphology and reproductive structures. You will be using live
specimens, herbarium pressings, and prepared slides.
Introduction
As beachcombers observe large mounds of beach wrack following storms, brown algae
typically make up a prominent portion of their biomass, especially off the west coast of North
America. The brown algae include the large kelps that form beds that dominate the subtidal
habitat in the temperate to polar regions of the world, where the marine environment is
fertilized by upwelling. Brown algae are of large economic importance and are consumed as
a “sea vegetable” in many regions of the world, and are harvested here in California as a
source of alginic acid.
Brown algae are the predominant algae in the intertidal and subtidal zones of cold
temperate to polar regions, becoming progressively less conspicuous at lower latitudes.
Brown algae are usually not found at depths greater than 90 feet, although some, such as
the giant kelp Macrocystis pyrifera, are the largest of the algae and may reach lengths in
excess of 150 feet. Algae as large as this are found along the west coast from Alaska to
California. The greatest degree of tissue differentiation occurs in this group. No unicellular
forms are known and only certain reproductive structures (zoospores and some gametes)
are planktonic. The evolutionary origins of these organisms remain obscure.
Algae in the class Phaeophyceae are almost entirely marine and are characterized by the
presence of two dissimilar flagella (heterokontic), which are laterally inserted in kidney-bean
shaped (reniform) reproductive bodies. Brown algae contain chlorophyll a and c, b-carotene,
and an accessory xanthophyll pigment (fucoxanthin). This latter pigment gives most brown
algae their characteristic brownish-green coloration. The cell walls of many brown algae are
composed of two components: cellulose microfibrils provide the main structural support
while alginic acid (a mucopolysaccharide) functions to protect the thallophytes from
desiccation and freezing, as well as provide flexibility and elasticity to the thallus. Alginates
(the salt form of alginic acid) are extracted from some of the “giant” kelps (Laminariales) and
have many human uses: such as preventing ice crystal formation in ice cream, preventing
frosting from drying out, and acting as an emulsifying agent in paints to keep pigments
suspended in solution and prevent brush streaking.
Morphology
The Ochrophyta (Class Phaeophyceae) includes forms which range from simple branched
filaments to extremely complex parenchymatous tissues with differentiated conductive
(sieve-like) cells. Unlike green algae, browns have no unicellular forms. However, the
browns do include filamentous, parenchymatous, complex parenchymatous, and
pseudoparenchymatous forms.
Systematics
Each order in the brown algae is characterized by genera having similar life histories and
patterns of development from a single celled zygote to a mature vegetative thallus. The
following table and list describe orders we will consider within the class Phaeophyceae.
Orders
Distinguishing Between Orders within Division: Heterokontophyta
Class: Phaeophyceae
Life History
Sexual Reproduction
Growth
Thallus Construction
Dictyotales
Alternation of
Generations:
- Isomorphic
Oogamy
- Apical
- Marginal
Ectocarpales
Alternation of
Generations:
- Isomorphic
- Heteromorphic
- Morphological
isogamy with
functional anisogamy
- Oogamy
Isomorphic Species
- Diffuse
Heteromorphic species
- Sporophyte: Trichothallic
- Gametophyte: Apical
- Filamentous
- Pseudoparenchymatous
Morphological isogamy
with functional
anisogamy
- Sporophyte: Trichothallic
- Gametophyte: Apical
- Filamentous
- Pseudoparenchymatous
Ralfsiales
Desmarestiales
Alternation of
Generations:
- Heteromorphic
Oogamy; eggs
sometimes flagellate
Laminariales
Fucales
Diplontic
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Oogamy
Mostly oogamy
Trichothallic
- Sporophyte: Intercalary
- Gametophyte: Apical
(Sze) - Meristodermal
Apical
Parenchymatous
Gametophyte (small)
filamentous
Sporophyte (large)
pseudoparenchymatous
Gametophyte (small)
filamentous
Sporophyte (large)
Parenchymatous
Parenchymatous
Taxonomy/Classification for Brown Algae
Domain: Eukaryota
Group: Chromista
Division: Ochrophyta
Class: Phaeophyceae (~2,059 species – 99% marine)
Notebook Requirements (16 drawings)
1) Fucus gardneri- 2 drawings (thallus and conceptacle cross section)
2) Silvetia compressa- 2 drawings (thallus and conceptacle cross section)
3) Pelivetiopsis limitata- 2 drawings (thallus and conceptacle cross section)
4) Stephanocystis osmundacea- 1 drawing (thallus)
5) Sargassum muticum- 1 drawing (thallus)
6) Ectocarpus- 2 drawings (plurilocular and unilocular material)
7) Haplogloia andersonii- 2 drawing (thallus and reproductive structure)
8) Dictyota binghamiae – 2 drawings (thallus and prepared slide)
9) 2 Unkowns - 2 drawing (thallus) and steps in key
A. Order Fucales
Family Fucaceae
Species: Fucus gardneri (hint: name change)
1. Examine and draw the entire thallus, noting the branching pattern. Look
for and label receptacles and conceptacles.
Q: What type of growth does the alga exhibit?
2. Cross section through a conceptacle. Find and label: oogonia, eggs,
antheridia, and sperm (sperm may not be visible but are found in the
antheridia). You can view these reproductive structures on permanent
slides if you want to see a clear view of structures, but you should also
look at live specimens (you should be familiar with both live specimens
and prepared slides for practical).
Q: Is this species monoecious or dioecious? (hint: the answer varies
between live and fixed material)
Q: How many eggs are found in the oogonia?
Q: What type of life history does this alga exhibit?
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Species: Silvetia compressa (formerly Pelvetia fastigiata) and Pelvetiopsis
limitata
• For this exercise you will be given the two genera listed above but you will
not be told which is which, your job will be to figure that out using your
MAC, Marine Algae of California book.
•
Cross section through a conceptacle of each species draw what you see
(you may work in pairs for this, i.e. one partner cross sections Silvetia and
the other Pelvetiopsis).
Q: How many eggs are in each oogonium for each species? Read the
Genera descriptions for the above species in your MAC. This
information along with your cross section should allow you to determine
which Genera you are observing.
•
Finally, quickly sketch the entire thallus of Silvetia and Pelvetiopsis.
Q: Explain how you figured out which alga is which
•
Write some notes about how the two forms are similar and how they are
different. (i.e. if you were in the field and could not do a cross section how
would you tell the two genera apart).
Family: Cystoseiraceae
Species: Stephanocystis osmundacea
1. Examine and draw the entire thallus. Thalli is perennial differentiated into
holdfast, stipe, and branches. Lower thallus persists while upper thallus
renews each year with distinctly different morphology. Note where this
occurs.
Q: Where are the recepticalslocated on the thallus?
Q: What is the ecological advantage or disadvantage of the location of
recepticals?
Family: Sargasseaceae
Species: Sargassum muticum
1. Examine and draw the algae from the pressing. How does this
algadiffer morphologically from Stepanocystis.
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B. Order Ectocarpales
Species: Ectocarpus spp.
1. Examine the prepared slides of Ectocarpus plurilocular and unilocular
material. Contrast and draw the different types of reproductive material.
Q: What type of thallus construction does it have?
Q: What does each type tell you about the ploidy of the parent thallus?
Species: Haplogloia andersonii
1. Examine and draw the entire thallus under the dissecting scope. Draw
the reproductive material under the dissecting scope.
Q: What type of thallus construction does it have?
Q: Is the reproductive material unilocular or plurilocular?
Q: What is the ploidy of the thallus? How do you know?
C. Order Dictyotales
Species: Dictyota binghamiae
1. Examine pressing of Dictyota binghamiae and draw entire thallus
2. Examine prepared slides of oogonia, tetraspores, antheridia, and apical
region from Dictyota binghamiae. Draw what you see. How many cells
thick is the thallus?
D. Unknowns
Key to species the two unknown you are given, as you have done in previous
labs. Be sure to write out each step of your path in the dichotomous key. Draw
the alga.
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Life Cycle of the Laminariales
Diplohaplontic
e.g. Laminaria setchellii
antheridia
produce sperm
1N zoospores
1N gametophytes
syngamy
meiosis occurs in
unilocular sporangia
sori on
2N adult
oogonium
2N embryonic
sporophyte
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