Supplemental Lecture (97/05/03 update) by Stephen T. Abedon (email@example.com)
- Chapter title: Algae
- A list of vocabulary words is found toward the end of this document
- The algae most significantly are the dominant producers in the sea. However, the algal taxon is polyphyletic (polyphyletic because land-plants are algae descendants, and because the algae are probably a taxon rooted in various protists rather than a single ancestral algae or protist). Nevertheless, the algae basically consist of the plant-like organisms (particularly, they are chloroplast-containing eucaryotes) that for the most part live in the sea, but also in freshwater as well as moist terrestrial habitats and as lichen endosymbionts. Because of the vastness and productivity of the oceans, something on the order of 90% of all of the photosynthesis that occurs on our planet occurs by (or within) algae. In terms of significance to the continued existence life, therefore, algae as the world's dominant producers, play an equally dominant role in the world's ecology.
- "The aquatic habitat is a relatively benign and unchanging place, and its properties helped shape the organisms that live there. Because water supports the algal plant body, most algae lack rigidity, and usually undulate gently with water currents and waves. Since water surrounds the plant on all sides, individual algal cells absorb moisture and minerals directly from the surrounding water and have no need for specialized conduction tubes. Plant shape also reflects this direct contact with water: Most algae are quite flattened, which maximizes the surface area for absorbing water, minerals, and sunlight. Finally, reproduction can be asexual, involving the fragmenting of cells or body parts, or it can be sexual, with the production of eggs and sperm. The main secret to the algae's success is a range of photosynthetic pigments (not all found in the same organisms) that absorb the light of the different wavelengths that penetrate to varying water depths. Botanists use these same pigments to distinguish between red, brown, and green algae." (p. 479, Postlethwait and Hopson, 1995)
- Some Human Diseases Caused by Algae
- Amnesiac shellfish poisoning
- Paralytic shellfish poisoning
- Overview (of algae)
- The following is quoted from Prescott et al., 1996 (p. 520):
- Most algae are found in freshwater and marine environments; a few grow in terrestrial habitats.
- The algae are not a single, closely related taxonomic group but, instead, are a diverse assemblage of unicellular, colonial, and multicellular eucaryotic organisms.
- Although algae can be autotrophic or heterotrophic, most are photoautotrophs. They store carbon in a variety of forms, including starch, oils, and various sugars.
- The body of an algae is called the thallus. Algal thalli range from small solitary cells to large, complex multicellular structures.
- Algae reproduce asexually and sexually.
- (Algae divisions include:) Chlorophyta (green algae), Charophyta (stoneworts/brittleworts), Euglenophyta (euglenoids), Chrysophyta (golden-brown and yellow-green algae; diatoms), Phaeophyta (brown algae), Rhodophtya (red algae), and Pyrrhophyta (dinoflagellates).
- Phycology [algology]
- Phycology (a.k.a., algology) is the study of algae.
- Eucaryotic photosynthesizers/not plants:
- "The word phycology is derived from the Greek phykos, meaning seaweed. The term algae [s., alga] was originally used to define simple 'aquatic plants.' In no longer has any formal significance in classification schemes. Instead the algae can be described as eucaryotic organisms that lack roots, stems, and leaves but have chlorophyll and other pigments for carrying out oxygen-producing photosynthesis. Many can be placed in the kingdom Protista." (p. 521, Prescott et al., 1996)
- Though algae lack the roots, stems, and leaves of land plants, they often have analogous structures such as holdfasts for attachment to bottom sediments and rock, or flattened bodies which maximize photosynthetic surfaces.
- Thallus [sing., thalli, pl.]
- Algal body:
- A thallus is the body of the vegetative form of algae.
- For single-celled algae, the thallus is just the single cell.
- For multi-celled algae, the thallus consists of the entire, continuous organism.
- There also exist complex algae that superficially appear to be macroscopic, multicellular organisms but, upon closer inspection, are found to actually consist of one giant, coenocytic (single celled) thallus.
- The algae habitat includes waters over a wide range of salinity as well as various water-atmosphere interfaces.
- Water living algae can be described as:
- There additionally exist numerous endosymbiotic and symbiotic algae.
- Particularly, endosymbiotic/symbiotic algae live in a variety of organisms including protozoa, mollusks, worms, corals, plants, and fungi (e.g., lichens).
- Some of these algae are parasitic.
- Free floating:
- The term planktonic means free-floating.
- Planktonare groups of free-floating organisms, not necessarily algae.
- Planktonic algae thus are water-living algae which are not attached to surfaces.
- The term planktonic contrasts with the terms benthic and neustonic.
- Phytoplankton are specifically the plancktonic producers, i.e., plankton consisting of algae, small plants, and photosynthesizing protozoa.
- Zooplankton are plankton consisting of animals and protozoa (i.e., non-photosynthesizing protists).
- Zooplankton are planktonic consumes.
- Non-free floating:
- Algae that grows in the water attached to a substrate are referred to as benthic.
- This contrasts with planktonic, i.e., the life style of phytoplankton.
- Air-water interface:
- Algae which live at the water-atmosphere interface are described as neustonic.
- Basically, this means algae which live on land in moist environments or at the edge of aquatic habitats.
- Silica shelled algae:
- Diatoms are algae that are planktonic and encased in two piece silica "shells" which fit together as do the two halves of a petri dish.
- Diatoms are found in fresh water, salt water, and even moist terrestrial habitats.
- Diatoms are the dominant phytoplankton in cooler oceans and consequently contribute immensely to the ocean's productivity.
Green algae [Chlorophyta]
- Large brown algae:
- Kelp are large (often very large) brown algae which live in the sea.
- Kelp display well differentiated thalli.
Red algae [Rhodophyta]
- Plant ancestors:
- Green algae were the likely the algal ancestor of terrestrial plants.
- Green algae have photosynthetic apparati which are very similar to those of plants.
- In addition, green algea, like plants, store their carbohydrate as starch (unlike other types of algae which store their carbohydrate in chemically different forms).
- The photosynthetic apparatuses of green algae are optimized for the capture of those photons which have not passed through large columns of water, i.e., only the atmosphere and to the bottom of shallow waters.
- The pigment which gives red algae their name contributes to their ability to efficiently photosynthesize at significant depths (100 meters or more).
- Agar, a sulfated polymer of galactose, is harvested from red algae.
- The dinoflagellates are:
- fresh water and marine
- protistan algae
- Dinoflagellates form the base of many fresh- and marine-water food chains.
- Some dinoflagellates are capable bioluminescence and they are responsible for the phosphorescence of oceans waters seen at night.
- Dinoflagellates are also responsible for toxic algal blooms such as red tides.
Toxic algal blooms
- A bloom is a local rise in numbers (and concentration) of algae.
- Not particularly desirable:
- Blooms are the cause of such things as toxic red tides.
- Blooms of certain kinds of algae are often a sign of pollution, especially of organic materials.
- Following blooms, algae death and subsequent decomposition can deplete dissolved oxygen in water thus making the habitat unsuitable for organisms requiring dissolved oxygen such as fish.
- Human disease:
- Various algae can produce substances toxic to humans (and other non-sea-living animals). These toxins may accumulate, to no harmful effect (but especially following algal blooms) in certain sea organisms such as filter feeding shellfish.
- Consumption of contaminated shellfish is associated with such human conditions as:
- paralytic shellfish poisoning (which numbs the face and extremities for a few days post-ingestion)
- ciguatera (which causes distress and dysfunction in all sorts of systems including the respiratory system, the nervous system, and the gastrointestinal system)
- amnesiac shellfish poisoning (which leads to a loss of short term memory---the ultimate "lost car keys" syndrome)
- "Overall, toxic algal blooms are on the rise. No one is certain why this is occurring, but most phycologists believe that the blooms are caused by the continuous pumping of nutrients such as nitrogen and phosphorous into coastal waters. Sewage and agricultural runoff are probably major sources. Another possibility is world trade: oceangoing ships are unintentionally trafficking in harmful algae, giving the algae a free ride to foreign ports and new habitats in which they can flourish. With people eating more seafood, this toxic menace in the world's oceans will become increasingly more common." (p. 529, Prescott et al., 1996)
- Green algae
- Human diseases caused by algae
- Red algae
- Toxic algal bloom
Practice question answers
- Where might you expect to find benthic algae? [PEEK]
- What kind of algae are responsible for the phosphorescence of ocean waters? [PEEK]
- attached to an underwater rock (on a sunlight exposed surface).
- Postlethwait, J.H., Hopson, J.L. (1995). The Nature of Life. Third Edition. McGraw Hill, Inc., New York. pp. 479-482.
- Prescott, L.M., Harley, J.P., Klein, D.A. (1996). Microbiology. Third Edition. Wm. C. Brown Pub. Dubuque, Iowa. pp. 520-531.
- Raven, P.H., Johnson, G.B. (1995). Biology (updated version). Third Edition. Wm. C. Brown publishers, Dubuque, Iowa. pp. 616-618, 622-623, 627-628, 629.
- Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA, pp. 304-313.