Interpretation of Algae

Interpretation of Algae / Protozoan Identifications

Algae are usually defined as organisms that contain chlorophyll compounds and have light dependent metabolisms. These organisms may be macroscopic (large) or microscopic (small).

The microscopic algae are divided into a number of groups.

A) Chlorophyta = Green Algae

These organisms may be unicellular, colonial or filamentous. They all contain 2 chlorophyll pigments (a & b), 2-3 carotenes and a number of xanthophylls (6-10). The grass-green chlorophyll predominates giving the group its name.

All organisms in this group are motile using flagella at some time in their life cycle (swimming vegetative cells or motile reproductive elements).

B) Cyanophyta = Blue-Green Algae

These organisms are unicellular, colonial or in filaments. There are all prokaryotes (bacteria) and contain chlorophyll a, upto 3 carotenes, xanthophylls (2-15), phycoerythrin and phycocyanin pigments.

C) Chrysophyta = Yellow-Green/Brown Algae

These algae occur as single cells or colonial. They are rarely filamentous. pigments are found in chloroplasts in which the yellow, or brown/yellow colours predominate. Food is stored internally as oil or leucosin. Vegetative and reproductive cells are usually motile with 2 flagella of unequal length. Many organisms belonging to this group are capable producing cysts.

D) Euglenophyta

Euglenoids are single celled motile organisms. Pigments include chlorophyll a & b, carotenes (4), and xanthophylls (1-5). Some also contain haematochrome. Pyrenoids are present and internal food storage includes insoluble starch, paramylum and fat compounds. Most members are capable of producing cysts.

E) Cryptophyta

Cells exist as solitary units or rarely as colonies. These organisms are motile with 2 flagella of unequal length. Brown, blue or red pigments predominate in large chloroplasts. Most store starches as food reserves.

F) Pyrrhophyta = Dinoflagellates

These are solitary organisms (few marine species are filamentous). They are motile with 2 flagella, one of which is found in a transverse furrow. Pigments include chlorophyll a, 2 carotenes, 4-6 xanthophylls, and phycopyrrin (red).

Food reserves include starches and oils.

G) Rhodophyta = Red Algae

These plants may be as singles, groups, colonial or branched filaments. All contain chlorophyll a & d, 2 carotenes, 3-14 xanthophylls phycoerythrin and phycocyanin.

Some things that the algal numbers and speciation may tell us:

A shift from dominate blooms of blue-green algae to diatoms or green algae can be from any one or combination of:

changes in C02 & pH
sinking rate
grazing by zooplankton
  • blue-greens tend to die-off with decrease in pH
  • blue-greens die-offs may be a result of viruses (viruses favored by low pH)
  • calm weather and stable thermal statifications favour blue-greens
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