Lab 1 – Photosynthetic Eukaryotes: The Algae
This lab introduces structurally simple eukaryotes of critical ecological importance: macroalgae, or
seaweed. Simple photosynthetic eukaryotes are responsible for most primary production in the sea,
and are habitat as well as food for many invertebrates.
When describing an alga ( the singular of algae, which is plural) include color, texture, slipperiness,
smells, and organisms found in association with it. Most algae have some way to anchor themselves
on the bottom, and all survive by harnessing the sun’s light for energy. Note features that seem
important for these purposes. Most algae also must defend themselves against being eaten, either
through physical defense (toughness, or hardening with minerals like calcium carbonate) or
chemical defense (bad-tasting chemicals). Touch and smell each alga, and record your observations.
Microscopic examination of algae is often the only way to tell species apart, or identify an unknown
specimen. Scientists use keys to ID an organism; you may be provided with keys for particular groups
throughout the course. Keys list the specific features that are diagnostic for a particular named species.
Use the information provided (keys, guidebooks) to identify algae in today’s labs.
Phaeophyta – the brown algae
STATION 1 – the giant kelp
This is Macrocystis, the giant kelp which grows in undersea forests off Californian coast. You have
here only a small piece of one stipe—a mature kelp could grow a piece this size in one day. Draw and
label the parts you can see by eye or under the microscope. Note any distinctive textures or smells.
What are the round parts, and what do you hypothesize is their function?
Where would the holdfast be, and what does it do? Describe it.
Cut off a piece and let it dry out for an hour or two to mimic a low tide. How does it look afterwards?
Re-wet it and see if it changes morphology again.
STATION 2 – the feather-boa kelp
Identify this brown alga, commonly called the feather-boa kelp; it is a relative of the giant kelp which
grows forests off the coast of southern California. Mature kelp can grow 3 feet in one day. Draw and
label the parts you can see (1) by eye, and then (2) under the microscope. What are the round parts and
what is their job?
Locate the holdfast; how do you think it works, based on its morphology? How does it compare to the
holdfast of Macrocystis from Station 1?
STATION 3 – “devil weed”, the highly invasive Sargassum horneri
This is an invasive species native to Asia that first appeared in southern CA in Long Beach harbor in
2003, then appeared intertidally in 2009. Since then, it has taken over huge areas on Catalina and is
increasingly common along our coast at all depths.
What are the clumps of what look like seeds on it? Compare and contrast this species to the other
browns. What are some ecological problems that could be caused by fast-spreading invasive algae like
this species?
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Chlorophyta – the green algae
STATION 4 – Ulva lactuca
This is the local green alga Ulva - draw and describe its overall appearance by eye, then examine it
under the microscope. Would you describe this species as more two-dimensional or 3D? Make a
sidewise slice through a flat piece and examine it in cross section – is the algal thallus just one sheet of
cells thick, or is it more than one layer thick? Is the center hollow or solid?
Can you see individual cells (and at what magnification)? Are there different cell types, or do all the
cells look the same? Can you locate the holdfast of this alga, and how does it compare to the kelps?
STATION 5 – the Caribbean alga Halimeda monile
In this dish, you will find a tropical calcareous alga in the genus Halimeda. Many green algae in the
tropics are calcified, meaning they deposit a calcium carbonate skeleton to make them harder to eat.
White sand on most tropical beaches is primarily composed of wave-pulverized Halimeda skeletons.
Examine one piece microscopically, and describe how its appearance under the scope is different from
its appearance to the naked eye. What is the texture of this alga like? How is the living tissue
distributed within (or on, or under) the calcareous skeleton? Do you see cell walls or subdivisions – if
not, what does this suggest about what kind of alga this is?
Locate the holdfast of this alga - how does it compare to the kelps?
STATION 6 – the Caribbean alga Udotea flabellum
Udotea is another calcareous alga from the tropics. Compare and contrast it with Halimeda, both in
terms of its appearance to the unaided eye, and under the microscope.
Rhodophyta – the red algae
STATION 7 – the foliose red Plocamium cartilaginum
This red alga is not calcareous, although many reds are calcified. How do you think a species like this
survives in the wave-crashing intertidal zone? Would you describe it as basically 2D or 3D?
Try a rough sketch of the overall morphology of one stipe, but remove a small piece and examine it
under the dissecting microscope to do a close-up drawing of the branching pattern. The way that side
branches form can be critical to identify species of algae using taxonomic guides. Does this alga smell
or feel different from other algae you’ve examined?
A marine angiosperm
STATION 8 – seagrass
This is the only organism in today’s lab that is a true plant. Algae are not plants, because they have no
tissues. Most land plants you are familiar with are angiosperms, which have vascular tissues for
transporting water and nutrients throughout the body of the plant, and complex organs. Identify this
plant, and draw and label features that would help you distinguish this plant from an alga. How is it
similar to, or different from, Ulva?
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