Biology of the freshwater diatom Didymosphenia: a review

Abstract

Features of the colonial diatom Didymosphenia are reviewed, especially D. geminata. Although there is a long record of its occurrence in north temperate regions, mass growths have been reported much more widely in recent years. Contrary to some statements in the literature, there are also reliable older records for the southern hemisphere, though the first report of mass growth was in New Zealand in 2004. The annual cycle of morphological changes in D. geminata in northern England, and probably elsewhere, includes a winter period when motile cells are attached to the substratum followed by spring when stalks start to develop. These raise cells into the water column and provide a site for phosphatase activity. Environmental factors associated with success include absence of extreme floods, high light, pH above neutral and nutrient chemistry. D. geminata often, but not always, occurs in waters where the N:P ratio is high for much of the year, but the key factor is the ratio of organic to inorganic phosphate. D. geminata thrives where organic P is predominant and the overall P concentration is low enough for organic P to be an important P source. It is unknown whether organic N can be used. Environmental changes increasing the relative importance of organic P are likely to favour D. geminata. Likely examples are increased N:P due to atmospheric N deposition and changes in form and seasonality of P release from organic-rich soils due to climatic warming. The nutrient chemistry of deep water released from dams to rivers also needs investigation. To what extent are genetic changes occurring in response to environmental changes and are new ecotypes spreading round the world? In spite of many adverse reports about D. geminata, such as detached mats blocking water pipes, there is still doubt about the extent to which it causes problems, particularly for fish. There have been few adverse effects on migratory salmonids in Europe and North America, but at least one report of harm to a brown trout population in USA. In New Zealand, it has caused serious problems for water sports, although it remains open to question how much adverse effect it has had on fish populations. If the presence of microcystins in or associated with D. geminata, as indicated recently for two populations, proves to be widespread and at sufficiently high concentration, their possible accumulation in fish requires study. Where control is required, this could Handling editor: Pierluigi Viaroli be achieved by enhancing the ratio of inorganic to organic phosphate in the water early in the growth season. Practical ways to achieve this are suggested.

Organic phosphate in UK rivers and its relevance to algal and bryophyte surveys

“…An extreme example of an organism whose competitive success almost certainly depends on the presence of organic phosphate is the diatom Didymosphenia geminata (Whitton et al, 2009). Rivers and streams with Didymophenia often drain catchments with peaty soils overlying base-rich rocks, such as the one in the R. Swale catchment where FHP formed on average 85% TFP (Ellwood et al, 2008).…”

Ecology, morphology and physiology ofChroothece richteriana(Rhodophyta, Stylonematophyceae) in the highly calcareous Río Chícamo, south-east Spain

“…Some internal differentiation was observed in the stalks (Fig. 6), and a distinct tubular structure was observed, such as occurs in the middle of the stalks of the colonial diatom Didymosphenia (Ellwood & Whitton, 2007;Whitton et al, 2009;Aboal et al, 2012), where it has been suggested it may aid rapid transfer of phosphate to the cell, such as might occur with a gradient resulting from rapid P uptake by the cell.…”

Invertebrate Composition and Abundance Associated withDidymosphenia geminatain a Montane Stream

“…Recent research has focused primarily on the biology and distribution of D. geminata (Kawecka and Sanecki 2003, Kilroy et al 2005, Kilroy et al 2006, Kirkwood et al 2007, Spaulding and Elwell 2007, Whitton et al 2009). Other recent research on invertebrate communities has shown that invertebrate composition tends to shift from larger taxa (i.e., Ephemeroptera, Plecoptera, Trichoptera) to smaller taxa such as Diptera in areas impacted by D. geminata (Shelby 2006, Shearer et al 2007, Larson and Carreiro 2008, Gillis and Chalifour 2009, Kilroy et al 2009).…”