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Life in Freshwater

Algae - filamentous

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Filamentous green algae magnified 100x

Often by mid-summer a pond becomes covered in green blanket weed. Pulling at it reveals hair-like strands. This is a type of filamentous green alga. Each strand is a length of cells joined end to end, all identical. In the example above this formation can be seen and each cell has small green dots, the chloroplasts, randomly distributed. The example below has the chloroplasts arranged in a spiral. This is the most easily recognised species, Spirogyra.

Filamentous algae is typically found in ponds but any water body may have at least some of this prolific producer.
Spirogyra

ECOLOGY: The blanket covering of a pond with this algae is invariably a response to high nutrient levels, especially nitrate. This could be run-off from farmland or just a natural occurrence as a pond reduces in size as water evaporates and concentrates the nutrients. Ponds and small lakes with dense algae like this may be said to be eutrophic.

Reproduction is rapid in warm conditions. Cells divide and increase the lengths of the filaments. In harsh periods, such as autumn, adjacent filaments may conjugate. This is where the contents of one cell merge with another. This causes genetic variation and results in a spore surviving the difficult period. If the pond dries up completely then the spores will be blown away to colonise another water body.

Filamentous algae yield a minimum of food for freshwater life but upon dying will produce detritus.


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