: AQUATIC PHYCOMYCETES 



out by incursion of the fungus. An epidemic in the bisporangia of the 

 red alga Seirospora in the Mediterranean caused by Petersenia lobata 

 recorded by J. and G. Feldmann (1940). In this instance, the host 

 plant reproduces by other means as well, hence, the balance of the 

 population was little disturbed. On the other hand, in an attack on the 

 epiphytic red alga Falkenbergia by a species of Olpidiopsis more than 

 70 per cent of the essential apical cells of the host were invaded, and 

 Traiiliella was similarly parasitized (Aleem. 1952b). Since sporulation 

 of these last two algae occurs for only a brief period ( they are sterile 

 the rest of the time), heavy infection may and probably does seriously 

 affect their population and limit their distribution. Aleem (op. cit.) 

 discusses the whole problem of phycomycete epidemics as it relates 

 to the marine habitat. He furnishes some evidence for the existence 

 of resistant races and host specificity. Incidentally, he (1952a) has also 

 recorded a fresh-water species of algal parasite (Myzocytium prolif- 

 erum) as causing epidemics in Spirogyra living in brackish water (salin- 

 ity. 9.6-10.1 per cent). 1 



In ecological observations made on certain marine fungal parasites 

 of algae from the west coast of Sweden and from the Mediterranean, 

 Aleem (1953) discovered that these fungi occur in both shallow and 

 deep water. Their absence in the littoral region was in most cases, he 

 found, due to the absence of the host plant. Some species will tolerate 

 a wide range of temperature and salt concentration — the diatom para- 

 site Ectrogella perforans. for example, might occur in waters that varied 

 from 14.6 to 38 per cent in salinity and at temperatures that ranged 

 from 5° to 30"' C. Aleem noted a similar adaptability in Pontisma 

 lagenidioides, an inhabitant of the red alga Ceramium. Earlier. Hohnk 

 (1939) had observed the opposite at Kiel in that the distribution of 

 en Phycomycetes he studied was influenced markedly by salt con- 

 centration^. -\t salinities lower than 16.8 per cent three of his marine 

 species dropped out: with increasing salinity zoospore formation was 

 inhibited and the production of gemmae favored in an unnamed species 

 of Saprolegnia. Among the factors favoring the spread of parasitic 

 marine fungi in a host population, that Hohnk noted, are crowding of 



1 Earlier, Stoll (1936) had isolated species of Achlya, Saprolegnia, Aphanomyces, 

 and Pythium from brackish water. 



