Educational Materials - Bookmarks
The PSA's three bookmarks ("Algae and Evolution", "Algae and Biodiversity" and "Algae and People") were produced in 2012 for distribution at the 2nd National Science and Engineering Festival in Washington, D. C. (April 26-28, 2012) and at other meetings. If you are interested in having any of these bookmarks, please contact the PSA's membership director for information on availability.
See below for a little information about each bookmark's algae and themes. We recommend these sources for additional information about the algae and their contributions to our planet:
1. Algaebase.org (on the home page, type the name of any alga into the search box under genus or species)
2. Graham, L. E., Graham, J. M. & L. W. Wilcox. 2009. Algae (2nd ed.). San Francisco: Benjamin Cummings, 616 pp. (a widely used college textbook on the algae).
3. Lee, R. E. 2008. Phycology (4th ed.). Cambridge: Cambridge University Press, 547 pp. (a widely used college textbook on the algae).
Bookmark 1: Algae and Evolution: Spirogyra sp. (Charophyta, Plantae; left panel); a sunflower (Plantae, middle panel); Gloeotrichia (Cyanobacteria or Cyanophyta, right panel).
Algae...live almost everywhere on Earth, are among the most ancient living organisms, and gave rise to all the plants you see and eat, including flowering plants such as sunflowers.
Gloeotrichia (right panel) belongs to the group of prokaryotic algae (cyanobacteria or blue-green algae) in which oxygen-evolving photosynthesis arose about 3 billion years ago. At that time, the Earth's atmosphere essentially lacked oxygen. The cyanobacteria are responsible for affecting the metabolism of later-evolving organisms due to their addition of oxygen to the atmosphere. Not only did this become a necessary gas for respiration in most organisms, including humans, but the oxygen gave rise to the ozone layer in the atmosphere, which protected living organisms from harmful ultraviolet radiation.
Gloeotrichia is microscopic and is found growing as colonies on the bottom in freshwater habitats, but sometimes detaches and floats in the water as part of the plankton.
Spirogyra (left panel) forms green, floating masses in freshwater lakes and vernal pools, especially in spring. Under the microscope, the spiral-shaped chloroplasts of each cell are evident, as in this beautiful micrograph of parts of three filaments. This alga is eukaryotic, which means that each cell has a true nucleus (in contrast to the cyanobacteria, where the DNA is loose in the cytoplasm, hence "prokaryotic"). Multicellular, eukaryotic green algae (Chlorophyta) are known as fossils dated to be 900 million years old;Spirogyra is part of a more recently evolved lineage of green algae from which terrestrial plants such as mosses, pine trees, and sunflowers evolved. These green algae (e.g., Spirogyra) and higher plants (e.g., sunflower) are classified in the same scientific group (Charophyta) in the Kingdom Plantae by some scientists because of their close evolutionary relationship. The particular type of charophyceaen green alga from which terrestrial plants evolved remains unknown, but multi-gene studies are providing data that may reveal this soon.
Bookmark 2: Algae and Biodiversity: The Sonaran Desert in Arizona (left panel), A Macrocystis pyrifera kelp forest off California (middle panel); A close-up of a fish and Macrocystis (right panel)
Algae...build coral reefs and kelp forests, are food for fish and even some whales, and are every color of the rainbow.
Some corals are small, and other coral species build massive reefs. All reef-building corals contain symbiotic dinoflagellate algae ("zooxanthellae", classified in many subgroups of the genus Symbiodinium). The algae carry out photosynthesis and as much as 95% of the sugars and other molecules made in photosynthesis are secreted by the dinoflagellates into the animal (coral's) cells, where it is used for food that supports growth, reproduction and calcification. The animal cells excrete "waste" that is nitrogen (N) and phosphorus (P) rich---N and P are required by the dinoflagellate cells for photosynthesis, growth and reproduction: A perfect symbiosis! In addition to building coral reefs, algae also build structure in many other habitats, including deserts and kelp forests.
The Sonaran Desert, Arizona (left panel): The darker patches on the desert soil between the bushes are cyanobacteria, green algae, diatoms, and eustigmatophycean algae that live in soil communities of arid and semi-arid habitats around the world. These algae have special adaptations to allow them to live for long periods -- sometimes years -- without water. These algae stabilize desert soil against wind erosion.
Kelp forests (middle and right panels) are common around the world in cold ocean waters, including in some deep, cold waters near the equator. Macrocystis kelps grow to be 30 meters long. They are considered to be "bioengineers" because they create so much structure for a diversity of other algae, invertebrates, fishes, and marine mammals to live and feed. Kelps are brown algae, but this brown color is hard to see in deeper water (middle panel). This is because the rainbow spectrum of colors in sunlight is absorbed differently by seawater. Red and orange are absorbed by seawater in the first few meters below the surface, and the deeper ocean looks blue to green as a result of the better penetration of those parts of sunlight. With a flash bulb (right panel), the true brown color of Macrocystis is revealed. The brown color is due to fucoxanthin, an accessory pigment to the green chlorophyll that is also present in kelps and all other algae. Different types of algae have different accessory pigments that fit the light environments of their many different habitats: the surface of trees, the hair of sloths, on hard surfaces at different depths in freshwater streams and lakes and oceans, and planktonic habitats of different depths in marine and freshwater habitats. As a result of these different colored pigments----brown, red, yellow-green, blue-green, orange and yellow, as well as the green chlorophylls that are always present---algae are every color of the rainbow!
Algae, from single-celled plankton to the huge kelps, provide food for many animals that graze on them. For example, kelps are food for sea urchins, some crabs, and some fish. The baleen whales, such as the blue whale, feed on phytoplankton that include diatoms and haptophytes. An example of a diatom that whales feed on directly is Coscinodiscus (see the next bookmark). The algae are at the base of the food-web in every aquatic and marine ecosystem, while being important components of many terrestrial communities.
Bookmark 3: Algae and People. A crab close-up against Macrocystis pyrifera (far left); the red algaOsmundea hybrida, covered by oxygen bubbles in an Irish rock-pool (middle left); the green algaBotryococcus braunii secreting oil (middle right); Coscinodiscus radiatus, a marine planktonic diatom (far right).
Algae...produce half the oxygen in the air you breathe; are used to make medicines, toothpaste and ice cream; and can become fuel for cars.
Alginate extraction from brown seaweeds (far left): Large marine algae need mechanical strength to grow above the bottom, but they must be flexible because of the force of water motion in the ocean. Cell walls of such algae typically contain polysaccharides that bind water well to provide this "cushioning" mechanical strength. These include agar and carrageenan in the cell walls of certain red algal species (e.g., agar fromGelidium and Gracilaria; carrageenan from Kappaphycus and Irish Moss, Chondrus crispus), and alginate from cell walls of brown seaweeds. Seaweeds belonging to the scientific orders Laminariales (e.g.,Macrocystis, Laminaria) and Fucales (e.g., Ascophyllum) are harvested throughout cold temperate regions of the ocean for alginate. Each of these polysaccharides is extracted commercially, and used in many food products and manufacturing processes that require a gelling agent or an emulsifier: see how many you can find in the products you use everyday (e.g., ice cream, toothpaste). Agar is used in hospitals and many scientific laboratories in applications that help to diagnose illness. Agarose gels are used to separate RNA and DNA molecules in many types of scientific research in laboratories all over the world. We've designed an alginate gel exercise that will let you explore this valuable compound.
Oxygen production from algae (middle left panel): All algae release oxygen in photosynthesis. This process evolved in cyanobacteria (See Bookmark 1), and then spread to other algae and higher plants from cyanobacteria, at least 1.5 billion years ago (see "primary endosymbiosis" in the recommended textbooks). Higher plants are now important oxygen-producers, too, but 50% of the oxygen in every breath you take comes from algae!
In most habitats, the oxygen produced by algae in photosynthesis quickly diffuses from the alga into the water and from the alga into the air, but on a calm, sunny day in a tide-pool, it is easy to see algae covered with oxygen bubbles. This is shown here by the red alga Osmundea hybrida, photographed on a calm sunny day in Connemara (Ireland). All algae and plants take up carbon dioxide (CO2) from the atmosphere. They use CO2 to make sugars in photosynthesis, and they release life-sustaining oxygen (O2), which comes from water molecules that are split during photosynthesis. Incidentally, Osmundea often has a strong peppery taste, probably from the halogenated sesquiterpenoids and diterpenoids that they produce, which makes them less tasty to grazing animals (see Bookmark 2).
Oil (hydrocarbon) production from algae (middle right): Petroleum and oil shales are composed of fossil algae. When living, these algae made large quantities of long-chain hydrocarbons. An example of an alga that does this is the green alga Botryoccocus braunii (middle right panel), a colonial, planktonic green alga that is found throughout the world in freshwater lakes and streams. Colonies may appear in shades of green, yellow, orange or red. Botryococcus naturally produces copious amount of hydrocarbons (triterpene oils) that assist in colony buoyancy and serve as a reserve food source. Although blooms of Botryococcusare infrequent, when they do occur, the oils released into the water can form an oily-sheen appearance that is often mistaken for a fuel leakage from power boats. There is intensive ongoing research onBotryococcus, other green algae, and diatoms (also oil-producers) to try to develop appropriate species to produce algal biofuels, thereby reducing dependence upon fossil fuels.
Scientists estimate that about 20% of all the photosynthesis on Earth today is carried out by algae called diatoms (e.g., Coscinodiscus radiatus, a marine, planktonic diatom; far right): Diatoms are often the most abundant algae in the plankton, especially in spring blooms in the ocean. Fish and marine mammals depend upon such planktonic algae, either directly, or by feeding on zooplankton (e.g., small, shrimp-like crustaceans) that have fed on the phytoplankton. Not all diatoms are found in the plankton. Many diatoms live on the surfaces of large, multicellular algae or sand or rocks in marine and freshwater habitats. The cell of each diatom sits inside two glass (silica) valves that are made and secreted by the diatoms; imagine a round hat [the cell] inside a hat box [ the two valves].
The Coscinodiscus shown here has glass valves that are between 30 and 180 µm in diameter; the larger-sized ones are just visible to the eye as specks (including to a salmon's eye!). The cell shown here is in the middle: 90 µm in diameter. Its valves are very flat and not very thick. The valves are sculpted as they are made (silicification), and the geometry of each species' valve is different, although this often has to be observed and described by scientists using a scanning electron microscope. Here, the valve's small pores (areolae) radiate in distinct rows from the valve's center, with a central rosette of slightly larger areolae. C. radiatus is a cosmopolitan species in the marine plankton of polar to temperate oceans.
Diatoms are an important part of the "biological pump" by which carbon is transferred from the atmosphere (CO2) to form sediments in the deep sea, because the protective silica valves mean that, when cells die, many drift down to the bottom before the carbon-rich cells completely decompose. "Diatomaceous earth" is made of fossilized diatoms, and it is a valuable commercial abrasive. The world's navies spend money to try to figure out how to keep diatoms from growing on ship hulls, because this creates friction, slows speed of the ship, and requires more fuel to get from one place to another. From the viewpoint of "Algae and People", however, oxygen-production, carbon-sequestration, and the large role of diatoms in marine and aquatic food-webs are especially important.