Filamentous Fungi of the Psammon Habitat at Enewetak Atoll, Marshall Islands

ABSTRACT

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.

Key Words:

• Enewetak Atoll
• Marshall Islands
• fungi
• beach
• mycoecology
• physiology