Lecture 10

Chlamydomonas, unicellular biflagellate
Volvox, colonial flagellate,
gelatinous matrix
Chlorophyta—green algae
•Nucleate,
•pigments contained within chloroplasts,
•vacuoles present,
•chloroplasts grass green (chlorophylls a & b)
•food stored as starches,
•cell wall of cellulose,
•mostly microscopic, some flagellate,
•some filamentous and some macrophytic
species
(1a)Flagellate(2)
(2a) Not flagellate(3)
(2a)unicellular, flagellate, with a cell wall
Eg Chlamydomonas
(2b) colonial, flagellated, with a gelatinous
matrix
Eg Volvox

(3a). Unicellular (4)
(3b) Colonial (5)
(4a)with a median constriction—Desmids
(4b) without a median constriction
Staurastrum
40 microns
Common in the plankton of lakes and ponds

Tetmemorus
Micrasterias
Closterium spp.
40 microns
Common in the plankton of
lakes and ponds

(4b) Cells without a median constriction—cells arcuate in shape,generally in a
loosely assembled colony--Ankistrodesmus
Cells
30-40
Microns
Long
A very
Common
And
Edible
Species
In the
Phyto-
Plankton
of lakes
and ponds

(5a) Colonies microscopic (6)
(5b) Colonies macroscopic or filamentous (7)
(6a) Colony a flat plateof radiately attached cells –Pediastrum
50 microns
Common in the
Phytoplankton of
Lakes and ponds

(6b) Colonies composed of lunate, sausage-shaped or curved cylindrical cells
laterally united, terminal cells often with spinous projections--Scenedesmus
Cells 20-30 microns
across

(7a) Colony a macroscopic net-like sac
Hydrodictyon
Hydrodictyon—chlorophyta—a meshlike bag of made formed by
cylindrical cells—its name means “water net”
The colony can be several cm in size. Blooms of Hydrodictyon can
dominate the plankton in eutrophic lakes, it is inedible to
zooplankton and other consumers

(7b) Cells connected end to end in filaments
(8a) filaments not branched eg. Spirogyra, Oedogonium
70 microns

(8b) Filaments branched eg Cladophora or Stigeoclonium
500 microns
Cladophora

Chara –-the stonewort
A macrophytic
Green alga

Ecology of Chlorophyta
•Few other algae have such a wide range of distribution and abundance as
chlorophyta
•Many even live in soils, and some grow on snow (red snow)
•Very important primary producers in the plankton of lakes, ponds, rivers and
streams—less important in oceans and esturaries.
•Smaller forms tend to be planktonic, whereas the larger filamentous forms usually
grow attached to surfaces such as rocks or other hard substrates.
•Many of the smaller filamentous green algae grow epiphytically on larger ones or
on aquatic macrophytes.
•Some grow mainly on, or within the tissues of animals as symbionts
•They are considered to be the ancestors of all higher plants (charophytes)
•They can form dense blooms in nutrient-rich waters.
•They are usually not toxic to animals, and are often very important nutritionally
•Some however, do cause taste and odour problems in water supplies.

Bacillariophyta—the diatoms
•thick bivalved ornate cell wall made of
silica (glass),
•Nucleate(1), vacuoles present,
•pigments contained within chloroplasts,
chloroplasts brownish (chlorophyll a plus
accessory carotenoids),
•food stored as oils,
•single celled (elongate or round) although
sometimes joined side-by-side or end-toend
as filaments
Some essential terminology
fr—frustule, cn—central nodule, r—raphe,
p—punctae, s—striae, c--costa
Valve view, girdle view
Pennate and centric forms

Diatom in valve view
Central area
Central nodule
raphe
stria
Terminal
nodule

Abbreviated diatom key
(1a)Pennate (2)
(1b)Centric or filamentous (14)
(2a) valves without a raphe (3)
(2b) with raphe (8)
(3a) with septa apparent in girdle view eg Tabellaria
(3b) without septa in girdle view (4)
(4a) valves with large costae in valve view (5),
(4b) valves without costae (6),
(5a) valves symmetrical to transverse axis Diatoma,
(5b) valves asymmetrical to transverse axis Meridion
(6a) valves symmetrical to transverse axis, not forming star-shaped colonies (7)
(6b) valves asymetrical to transverse axis, frustules forming star-shaped colonies--
Asterionella
(7a) frustules forming side-by-side colonies usually seen in girdle view eg Fragilaria
(7b) frustules not forming colonies, often seen in valve view eg Synedra
(8a)Valve symmetrical to both longitudinal and transverse axis (9)
(8b)Valve asymmetrical to either axis(12)

(9a)Frustule sigmoid, striae fine—Gyrosigma
(9b)Frustule not sigmoid, striae costate appearing as ribs(10)
(10a) raphe appearing as a wavy line, central area confined to a small nodule—Pinnularia
(10b) raphe appearing straight (11)
(11a) central area extending about half way to lateral margin of the valve—Navicula
(11b) central area very wide extending to valve margin--Stauroneis
(12a) Valve asymmetrical to transverse axis—eg Gomphoneis
(12b) Valve asymmetrical to longitudinal axis (13)
(13a) raphe fairly close to ventral margin, without distinct terminal fissures—Amphora
(13b) raphe closer to midline, with distinct terminal fissures—Cymbella
(14a)Frustules forming long filaments, cells seen in girdle view, girdle conspicuous joined
to valve mantle by a conspicuous groove—Melosira
(14b)valves circular or radially symmetrical, usually seen from valve view, margin of valve
marked by coarse costae or fine striae—Eg Cyclotella or Stephanodiscus

Usually found attached to rocks--periphyton

Usually found attached to rocks--periphyton

Meridion
Costae evident in valve view
Usually found in periphyton or as epiphytes
On macrophytes or filamentous green algae

Fragilaria colony cells joined side-by-side
in girdle view, generally planktonic
Valve view (on the left)
Each cell 50-70 microns

Synedra
Abundant in periphyton
About 100 microns long

Asterionella
Fairly large for planktonic diatoms
Each spoke around 50-70 microns
Commonly found in dense blooms
during May, prior to the onset of
thermal stratification

Gyrosigma
Around 100 microns long
Abundant in periphyton

Pinnularia about 100 microns
Abundant in periphyton

Navicula
Abundant in periphyton

Abundant in
periphyton

Gomphoneis
Abundant in periphyton

Melosira
A filamentous diatom-each cell around 20 microns long
In the phytoplankton of lakes in the spring, but sink rapidly into the
hypolimnion during the summer months
Some species grow attached to rocks in streams

Cyclotella (around 20 microns) and Stephanodiscus (around 50 microns)
Usually abundant in spring plankton

Ecology of diatoms
•Extremely important primary producers in lake and ocean phytoplankton, and
in the benthic algal communities of lakes and streams.
•Species that have a raphe are able to move slowly around 0.2-25/sec. This is
very slow, and with their siliceous frustules they tend to sink rapidly, unless
they have elaborate cell extensions.
•Diatoms often form dense blooms in silica rich cold waters, mainly spring and
fall, when the water column is well-mixed
•Many species are extremely edible to small animals and are an important
source of nutrition for them
•Most diatom species have narrow limits of tolerance and preference for
chemical conditions in the water example, pH, alkalinity, salinity, Ca, P, N,
organic matter, pollutants of various kinds, as well as temperature.
•This, together with the fact that diatoms are so abundant and preserve well in
sediment cores, makes diatoms very useful as indicators in paleolimnology.

Epiphytic diatoms

Asterionella
A planktonic diatom—blooms
in early spring in oligotrophic
and mesotrophic lakes

A variety of pennate diatoms
Most grow attached to rocks
and other hard substrates in
streams or along lakeshores