J. W. G. Lund

Studies on plankton parasites: II. The parasitism of diatoms with special reference to lakes in the English Lake District

In a survey of the incidence of parasitism of plankton diatoms by chytridiaceous fungi in the English Lake District particular attention has been paid to the occurrence of fungi on Asterionella formosa and Fragilaria crotonensis , and to the effect of parasitism on their seasonal distribution. Almost all the plankton diatoms are infected by fungi, some of which are described, including: Rhizophidium planktonicum, Chytriomyces sp., Zygorhizidium planktonicum Canter, n.sp., and Septosperma anomala on Asterionella formosa; Zygorhizidium melosirae, Septosperma sp., and? Rhizophidium fusus on Melosira italica ; and Chytridium versatile on Tabellaria . Some of the parasites cannot be named until further details of their life history are known. Parasites of plankton diatoms are also recorded from other bodies of water in Great Britain and various parts of Europe. Fluorescence microscopy has been used to follow the effects of parasitism on the host cells. The occurrence of bacteria on two of the fungi is discussed.

Population dynamics of Ceratium spp. in three English lakes, 1945–1985

Changes in the annual population densities of Ceratium spp. in three adjacent English lakes, Windermere, Esthwaite Water and Blelham Tarn, are summarised over the 41 year period 1945–1985. In these lakes the genus is represented by two species, C. hirundinella (O.F. Müll) Bergh. and C. furcoides (Levander) Langhans. Although the species have not been distinguished over the entire study period, they have been shown by examination of preserved samples to undergo marked changes of relative abundance in Esthwaite Water. Both long-term (years) and short-term (within year) changes of populations densities of Ceratium spp. are considered in relation to possible controlling factors including recruitment of the inoculum, nutrient enrichment, physical stability and fungal epidemics. Given an early inoculum, the relative success of Ceratium populations in these lakes decreases along gradients of increasing mixed depths, increasing turbulence and decreasing retention times. The potential for good population growth is regulated by energy inputs, lake bathymetry and hydraulic characteristics. The realisation of such growth is governed by nutrient availability and microbial grazing. The significance of large between-year differences of populations of Ceratium spp. for general lake metabolism is illustrated for summers of contrasting production in Esthwaite Water.

The parasitism of planktonic desmids by fungi

Desmids in Windermere, a lake in the English Lake District, are often parasitized by chytridiaceous or biflagellate phycomyceteus fungi. Descriptions are given of the fungal parasites concerned, several of which cannot yet be named. The relationship between the severity of parasitism, decrease in the number of live cells of desmids and increases in those of dead cells are described and illustrated. There is evidence, from over twenty years of observations on desmids and their parasites, that the examples given here are not peculiar to the years concerned and that parasitism occurs similarly in other lakes. Parasitism does not alter the overall seasonal pattern of periodicity of the desmids; it can have a marked effect on interspecific competition. There is no evidence that desmids must be already adversely affected by other environmental conditions before severe parasitism can arise. Indeed the evidence available suggest that parasites commonly infect healthy and rapidly growing cells.

Studies on British chytrids: XXVII. Rhizophydium Fugax sp.nov., A parasite of planktonic cryptomonads with additional notes and records of Planktonic fungi

Rhizophydium fugax sp.nov. is described from the English Lake District parasitizing species of Cryptomonas . New records and/or hosts are given for Blasto-cladiella anabaenae Canter & Willoughby, Dangeardia mammillata Schroder, Endocoenobium eudorinae Ingold, Rhizophydium ubiquetum Canter, R. venustum Canter, Rhizosiphon anabaenae (Rhode & Skuja) Canter, R. crassum Scherffel, Zygorhizidium parallelosede Canter and Z. porvum Canter.

Studies on British chytrids: XXI. Chytridium confervae (Wille) minden

Further observations on the sporangial stage of Chytridium confervae are described and discussed in relation to the descriptions given by earlier workers.