FILAMENTOUS FUNGI OF THE PSAMMON HABITAT AT ENEWETAK ATOLL, MARSHALL ISLANDS

Enewetak Island, the largest of Enewetak Atoll, was the location for a study of the distribution of the heterotrophic microbial component of the marine psammon habitat in zones extending from land to subtidal. Zones were characterized by sand grain size and vertical distribution, salinity, temperature, pH, moisture, organic content, and oxygen level. Numbers of heterotrophic microorganisms were determined by plating methods using a wide spectrum of media under aerobic and anaerobic conditions. There was no correlation between numbers of microorganisms and organic content of sand. A decrease in numbers of bacteria, fungi, and Actinomycetes correlated with increased submergence time. Actinomycetes were common in the land zone but did not occur in the intertidal and subtidal zones. In samples taken at various depths in the subtidal, only bacteria were present in significant numbers in the black, anaerobic zone, although a few fungi occurred there. Of the 116 fungal species found, only 11 per cent were found in all zones. The land and black zones, by virtue of their distinctive features, had fewer than 20 per cent in common with the tidal zones. Application of Dice's similarity quotient to the fungal species isolated confirmed three zones of vertical distribution: land, tidal, and a black, anaerobic zone. Adaptation to the psammon habitat salinity and temperature was assayed in vitro. Propagules of 30 fungi maintained their viability in sand submerged in seawater for 5 wk. Spores of most species germinated within a wide range of salinities on enriched media. In vitro, the behavior of three out of five selected species displayed apparent adaptation to salinity and temperature conditions of the psammon habitat. The salinity optima of Actinomycetes were similar to those of the fungi. Studies of fungi in the marine psammon habitat have dealt largely with the shoreline of continental land masses in temperate climates with more attention to geographical occurrence than to mycoecology. Brown (1958) investigated the pH optima of English beach fungi, and Westheide (1968) considered the ecology of a North Sea beach heterotrophic community. Investigations of fungi in the marine environment of tropical and subtropical Pacific Islands are few (Johnstone, 1947; Sparrow, 1948; Steele, 1967; Kohlmeyer, 1969; Kishimoto and Baker, 1969; Anderson, 1979). Emphasis in these studies ranged from macrofungi to Phycomycetes, Actinomycetes, and human pathogens, and emphasized their occurrence. Anderson (1979) showed long survival of human pathogenic fungi in seawater and in Hawaiian beach sands in vitro based on in vivo parameters. Little regard has been given to the role of microfungi in the psammon habitat, a question posed by Sparrow as early as 1937. There is a group of Pyrenomycetes which is generally found on wood and algae in marine habitats. These are traditionally thought of as "marine fungi." The lignicolous and arenicolous marine fungi were not selectively sampled for in this study although they are present. Wood and macroalgae (with the exception of the coralline algae) are rare at Enewetak Atoll. Many species of higher fungi have been isolated from beaches as reviewed. Their activity in the beaches has not been established. Isolations were done with