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. © 1969 Springer-Verlag.