Infestation of Chytridiaceous Fungi on Phytoplankton in Relation to Certain Environmental Factors

• DOI: 10.2307/1933316
• Publication Date: 2006-05-03T20:13:58Z
• Authors: R. A. Paterson
• Keywords: 13. Climate action; 15. Life on land; 6. Clean water

The ecological role of the fungi in nature, particularly that of the aquatic fungi, has long been a subject for conjecture and speculation. These aquatic plants, with the bacteria and protozoa, are of great significance in the break-down of dead organic matter and in the returning of nutrient materials into the environment. The abundance and variety of aquatic fungi can be verified by microscopic examination of the silmy surface of an apple, an onion, a rose hip, or a wild cherry fruit which has been immersed for several weeks in natural waters. Kanouse (1925) states that zoospores of members of Saprolegnia, Achlya, and Pythiomorpha are probably present in most fresh water habitats. Weston (1940), who discussed the role of aquatic fungi in hydrobiology suggests that no type of inland water lacks representatives of the Phycomycetes and points out that members of practically all major groups of fresh water organisms are attacked by aquatic fungi. The only quantitative limnological studies of aquatic Phycomycetes appear to be the investigations of Canter and Lund (1948, 1951, 1953) in the English Lake District. They found that epidemic parasitism of the chytrid Rhizophydium planktonium Canter on the diatom Asterionella formosa Hass. delays the time of algal maximum or decreases the number of diatoms present during such a period. Parasitism by fungi of one species of algae may favor the development of other phytoplankters. The degree of infection of a population depends on the relative fluctuation in the numbers of fungal and algal cells. When conditions are suitable, a parasite can increase in numbers faster than its host, as evidenced by epidemics which preceded or followed the time at which the maximum numbers of algal cells were present. Often an epidemic occurs at the time of the decline in host maximum, which may cause an appreciable ecological effect since the decline is then earlier than it otherwise would have been. Canter and Lund point out that factors such as the amount of available silica in the water and the duration and intensity of light are difficult to correlate with degree of parasitism. This investigation was conducted at Frains Lake, Washtenaw County, Michigan, for one year. Two chytridiaceous fungi were studied. One, Rhizosiphon anabaenae (Rodhe and Skuja) Canter, was parasitic on the blue-green alga, Anabaena planktonica Brunnthaler (Fig. 1; B, C), and the other, Amphicypellus elegans Ingold, was saprophytic on dead thecae of the dinoflagellate, Cera-