Freshwater algae constitute a very diverse group of
organisms. Their range of shapes and beauty, when
viewed through a microscope, has delighted biologists for more than a hundred years. They have an
enormous range of size from less than one micrometre
to several centimetres (for the stoneworts) – equalling
the size span (104) for higher plants seen in a tropical rainforest. Algal morphology is diverse, ranging from single cells to complex colonies and filaments. Some species are capable of active movement. The term ‘algae’ embraces a number of phyla
(e.g. Cyanophyta, Bacillariophyta and Chlorophyta)
of chlorophyll-containing organisms with different
growth forms and cytologies. Algae are important
primary producers in both freshwater and marine systems. In many lakes and rivers, they generate biomass
which is the foundation of diverse food chains.
Although algae have beneficial impacts on aquatic ecosystems, they can also have adverse effects. When present in very large numbers they can produce ‘blooms’ that, on decomposition, deoxygenate the water – causing fish death and other ecological problems. Some algae produce toxins that are lethal to both aquatic and terrestrial organisms. It is important to be aware of these impacts and to monitor waters for the presence of these potentially harmful organisms. Algae can be used to flag up and assess a range of human and natural impacts in aquatic systems because of their often rapid response to changes in the environment. Examples include nutrient enrichment (eutrophication), industrial pollution and changes to the hydrological regime of the water body. Some groups of algae preserve well as fossils in geological deposits such as lake sediments, analysis of which gives us information on past environmental changes.
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