Blanket weed
Cladophora is one of the most common and speciose genera of green algae in the world. Not only are species found on every continent, there are species that occur in nutrient-poor and nutrient-rich freshwater through brackish waters to marine environments. Species may be attached to substrates or free-living, with some species forming spherical mats ('cladophora balls') up to ten centimetres in diameter.
Multicellular, filamentous, branched green algae found in such habitats are likely to be members of the genus Cladophora. In contrast to the ease of recognising the genus, Cladophora species are very difficult to differentiate due to the amount of variation within a species caused by factors such as habitat, age and environmental conditions, e.g., nutrient and light levels and water flow rates.
The German phycologist Friedrich Kützing first described the genus Cladophora (meaning 'bearing branches') in 1843; Linnaeus had put most filamentous algae into a single large genus called Conferva. Kützing went on to describe hundreds of new species without recognising the extensive morphological variation that can occur within a single species. The confusion was only added to by later taxonomists such that by the time phycologist Christiaan van den Hoek started his work on the genus in the 1960s there were more than 1,000 species recognised. Furthermore, the sexual and asexual phases of the Cladophora lifecycle look very similar to each other. Today at least 400 species are recognised but differentiation of species requires examination of minute characters.
Rough, yellow-green lumps of floating algae known as blanket weed are familiar to, and reviled by, pond lovers. Cladophora mats will frequently appear in the spring, and gradually turn white as they bleach and decay. When nutrient levels are low, vegetative cells of Cladophora can become specialised structures with thick walls that accumulate large amounts of starch as a food reserve. These cells remain dormant until conditions improve, when they can then develop and form new Cladophora plants.
Cladophora sometimes creates algal blooms, forming vast algal rafts that have diverse ecological and economic effects. Adverse effects include blocking irrigation systems and drainage channels, the reduction of fish spawning and increasing anoxia from decaying algae. The growth of Cladophora is known to be associated with phosphate pollution. During the 1960s massive Cladophora growth drew attention to ecological problems in the North America Great Lakes.
In parts of South East Asia, Cladophora species are frequently eaten as the delicacy Mekong weed.Further reading
Bryant J and Irvine L 2016. Marimo, Cladophora, Posidonia and other plant balls. The Linnean 32: 11-14.
Dodds WK and Gudder DA 1992. The ecology of Cladophora. Journal of Phycology 28: 415-427.
Higgins SN et al. 2008. An ecological review of Cladophora glomerata (Chlorophyta) in the Laurentian Great Lakes. Journal of Phycology 44: 839-854.
Stephen Harris