1.   Algae are a diverse collection of photosynthetic organisms

• Generally classified as protists
• Protists normally considered to be single-celled eukaryotes
• BUT, many algae are multicellular - some are huge organisms

• Algae are not a phylogenetically cohesive group - not monophyletic
• More generally, Protists are not a monophyletic group

3.  Generally, algae are divided into three main groups:

(1)  Green algae - Phylum Chlorophyta

(2)  Red algae - Phylum Rhodophyta

(3)  Brown algae and diatoms - Stramenophila

• Diatoms - Chrysophyta

• Brown algae - formerly known as Phylum Pheophyta

NOTE:

Several additional groups are often called algae as well

• many dinoflaggelates are photosynthetic

• many of the Euglenozoa are photosynthetic

• "blue-green algae" are are a group of phytosynthetic prokaryotes know as the cyanobacteria
• not true algae
• related to the algae, in that certain cyanobacteria gave rise to chloroplasts
  • so, actually, related to the cholorplasts in algae, and the chloroplasts of all other photosynthetic eukaryotes too!

4.  The 3 main groups of algae differ in a variety of ways:

• Different chlorophylls

• Different accessory pigments - these often give distinctive colors (e.g. in red and brown algae)

• Diverse life cycles - some algal life cycles are very strange!
• often have various forms of alternation of generations

5.  Green algae - Chlorophyta

• Very closely related to land plants (and have same photosynthetic pigments)

• Freshwater and marine (marine = saltwater)

• Very important in aquatic food webs

• Extremely diverse in form

• many are single-celled - often with flagella for swimming

• some are clusters of cells, or hollow balls of cells - often with flagella

• some are filaments - strings of cells

• some are very plant-like in form

• some are just downright wierd!

6.    Red algae - Rhodophyta

• Often are red, due to pigments that absorb blue light (which penetrates deeper into the water) and reflects red

• Not all species are red though - various species might be green, brown, blue, or other colors

See: http://www.ucmp.berkeley.edu/protista/rhodophyta.html

• Some live in freshwater, but most are marine

• extremely abundant and important in the ocean

• Diverse growth forms 

            See:

• some are very very small

• some are filamentous

• some are large and plant-like

• Often have outrageously weird and complex life cycles
• To get a hint at how weird they are, take a look at this link:

• red algae are so wierd that some biologists feel they should be classified as a separate kingdom!

• some form hard pink or purple branching structures or crusts on rocks

• these are called coraline algae

                    see photos

• secrete calcium carbonate as they grow
• strengthen growths
• deter many (but not all) herbivores

• coraline algae are abundant and important
• major contributors (along with corals) to the formation of coral reefs

• Some red algae are important foods for humans
• Nori - used in sushi - http://en.wikipedia.org/wiki/Nori
• agar, carageenan, etc

7.   Brown algae and diatoms

• Diatoms 

• Normally single-celled - many are planktonic, some attach to surfaces - More information

• Intricate shells made of silica compounds (glass)
• two halves  that fit together like small pill-boxes with lids - Lots of nice photos of pretty diatoms!

• Diatoms are abundant in fresh water and marine habitats
• and extremely important contributors to global photosynthesis

• Brown algae 

• Some live in freshwater, but brown algae are most abundant, diverse, and important in marine habitats.

• some are small, filamentous

• many are larger and plant-like

• some are HUGE, and extremely fast-growing -  e.g. giant kelps - see photo with diver!
• some of the large ones have tissues similar to the vascular tissues of plants

• Kelps are extremely important in some marine habitats, forming underwater forests several stories high.
• kelps are the foundations of some marine habitats, just as trees are the foundations of forests.
• entire ecological communities depend on kelps
• kelp forests tend to develop in relatively shallow coastal areas with high nutrients - e.g. the west coast of North America

                        See: http://life.bio.sunysb.edu/marinebio/kelpforest.html
                            

• Some types of kelp are eaten - kombu  http://en.wikipedia.org/wiki/Kombu
• Another very important brown alga is Sargassum
  • Several types of Sargassum grow floating in the ocean, forming large "rafts" in the Sargasso Sea
  • This "sargassum weed" provides living conditions for a diverse biological community
  • This is the breeding location for all of the freshwater eels in North America and Europe!

An additional interesting, sort of wierd, and VERY important group.... Dinoflagellates!

• Many cell shapes (see photos ) but a general characteristic is two flagella, with one in a groove encircling the cell - see diagram

  • flagellum encirling cell tends to make dinoflagellates spin as they swim

• Some are VERY ABUNDANT AND IMPORTANT as photosynthetic plankton in the ocean

  • along with certain cyanobacteria, diatoms, and green algae these dinoflagellates are responsible for a large proportion of the world's photosynthesis

• Some are very important symbionts of corals and anemones - Zooxanthellae

  • Provide many corals with as much as 90% of their energy

• Some are parasites of fish! e.g. velvet disease

• Some are very toxic and can cause illness in animals

  • red tides - "blooms" of toxic planktonic dinoflagellates - so abundant they color the water! Occur in many places, sometimes causing dieoffs of fish and other animals.

    • red tides are what gave the Red Sea its name!

  • ciguatera toxin in coral reef fish - from toxic dinoflagellates that live on reef surfaces and passed through food chains to predaceous fish

    • May have been reason for some migrations of Polynesians!

  • Some are bioluminescent and cause seawater to glow brightly at night!

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