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How to know the freshwater benthic algae

Maria Kahlert

freshwater benthic algae

Check first:• Color:

– Bluegreen: bluegreen algae– Green: green algae– Yellowish-Brown: brown algae

• Diatoms• Chrysophytes• Brown algae

– Red: red algae

Be aware of exceptions!!!

freshwater benthic algae

Exceptions in color:• Bluegreen red alga:

Chroodactylon• Green ‘brown’ alga:

Vaucheria• Green ‘brown’ alga:

diatoms in bad shape• Red green alga:

Haematococcus

freshwater benthic algae

Check also:• Absence/presence of cell organelles:

– Absence: bluegreen algae = cyanoBACTERIA

– Presence: all other algae

• Presence of siliceous cell wall (distinctly shaped ‘glass house’): diatoms

freshwater benthic algaeCheck next:• Bluegreen algae

– Organization of thallus:• Coccoid• Filamentous

– No branches– False branches– True branches

– Presence/absence and place of heterocysts (N2 fixation) (only for the filamentous forms)

– Length of cell

freshwater benthic algae

Check next:• Green algae

– Organization of thallus:• Coccoid

– Single cell/colonies/coenobia

• Filamentous– Not branched/branched

– Chloroplast morphology:• Cup-shaped• Parietal (like a tapestry, middle of cell is vacuole)• Axial (in the middle of cell)

freshwater benthic algae

Check next:• ‘Brown’ algae – Diatoms

– Identification of living diatoms only grossly, must be prepared (see separate information)

raphe (slit in cell wall)

no raphe

pennatecentric

freshwater benthic algae

Check next:• ‘Brown’ algae

– Chrysophytes and ‘real’ brown algaeVery few in freshwater, very different:• Hydrurus (golden)• Ophiocytium (green)• Tribonema (golden)• Vaucheria (green)• Pleurocladia (brown)• Hildenbrandia (brown)

freshwater benthic algae

Check next:• Red algae

– Very few in freshwater• Heribaudiella• Chroodactylon• Audouinella• Batrachospermum

freshwater benthic algaeSome algal terms• Cell organelles – cell content with a membrane

inside the cell• Siliceous cell wall – cell wall outside cell in diatoms,

made from glass• Heterocysts – special cells in bluegreens fixating N2

• Thallus – body of alga• Coccoid – ball formed thallus• Filamentous – hair formed thallus• Coenobia- cell cannot divide mitotically, after

meiosis, the mother cells dies and relieves a certain number of identically shaped daughter cells, a finished colony