Introduction to Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 19

Table 1.7 Range of Morphologies in Freshwater Green Algae.

Major Morphotype Attached or Planktonic Example

Flagellate Unicells Planktonic Chlamydomonas (Fig. 4.55)

Non-flagellate Unicells Planktonic or benthic (often

associated with periphyton)

Crescent shaped - Selenastrum (Fig. 4.78)
Equatorial division - Micrasterias (Fig. 4.81) Closterium
(Fig. 4.80)

Colonial Planktonic Net - Hydrodictyon (Fig. 4.1)

Hollow sphere - Volvox (Fig. 4.40), Coelastrum, Eudorina
(Fig. 4.39)
Solid sphere - Pandorina (4.36) Plate of cells - Gonium
(Fig. 4.38), Pediastrum (Fig. 4.47)
Small linear colonies - Scenedesmus (Fig. 4.50)
Branching colonies - Dictyosphaerium (Fig. 4.45)

Disk-shaped plate, one
cell thick

Attached to higher plants
(epiphyte) or to stones

Coleochaete, Chaetosphaeridium

Unbranched filaments Typically Attached, but may

detach to become
planktonic

Uronema , Microspora , Oedogonium (Fig. 4.17) , Zygnema
(Fig. 4.15), Spirogyra (Fig. 4.13)

Branched filaments) Chaetophora, Draparnaldia, Cladophora (Fig. 4.6)

Large complex algae
with whorls of
branches

Attached Chara, Nitella

colonial forms), Chlorococcales (unicells and non-
motile coenobial colonies), Ulotrichales (unbranched
filaments) and Chaetophorales (branched filaments).
More recently, the application of cytological, com-
parative biochemical and molecular sequencing tech-
niques has demonstrated the occurrence of extensive
parallel evolution. On the basis that classification
should reflect phylogeny, these original groupings
are thus no longer valid, and a new classification
is emerging where individual orders contain a mix-
ture of unicellular, globular colonial and filamentous
forms (Graham and Wilcox, 2000).

Algal Blooms

In mesotrophic and eutrophic lakes, green algae
do not normally produce the dense blooms seen
with diatoms and blue-green algae - but do become
dominant or co-dominant in early summer, between
the clear-water phase and mid-summer mixed algal
bloom. In smaller ponds, filamentous Spirogyra
and colonial Hydrodictyon frequently form surface
blooms or scums, and in small garden ponds and
birdbaths Haematococcus may form dense popu-
lations. When nutrient levels become very high, a
switch may occur from colonial blue-green to green
algae as major bloom formers. This is can be seen
in some managed fishponds, where organic and inor-
ganic nutrients are applied to enhance fish produc-
tion by increasing carbon flow through the whole
food chain. In the Trebon Basin Biosphere Reserve
(Czech Republic), application of lime (supply of car-
bonate and bicarbonate ions), organic fertilisers and
manure leads to high pH and hypertrophic nutrient
levels. In these conditions, a short diatom bloom

1.4.3 Ecology

Green algae are ecologically important as major pro-
ducers of biomass in freshwater systems, either as
planktonic (standing waters) or attached (running
waters) organisms - where they respectively may
form dense blooms and periphyton growths.