SUMMARYThe diatom population structure of a salt marsh epiphytic community growing onEnteromorpha intestinaliswas studied at one station throughout the summer. A total of 218 species or varieties were recognized. Six species— Fragilaria construens, Cocconeis scutellum, Cocconeis placentula, Achnanthes hauckianavarieties,Achnanthes pinnata, andAmphora coffeaeformis(var.acutiuscula)–dominated theEnteromorphaepiphytic community during the summer months and comprised ∼ 40% of the total populations.Melosira nummuloides, Opephora martyi, Synedra fasiculatavar.tabulata, S. affinis, Navicula platyventris, andN. pavillardiwere also very common species (13% of the total population). The distribution of many species in the community was seasonal. A series of differential media have been developed which are effective as tools for the isolation and nutritional characterization of the algae and bacteria from the community. Many diatom species can be recognized by their colony type or growth pattern on solidified media. A key and illustrated plates aid in identification. Changes in population structure of the community were reflected by changes in the nutritional patterns as judged by differences in the growth of diatoms and bacteria on the differential media tested. The nutritional requirements, selectivity, and rank order of media for individual species is given.Almost half of the colony types (32–33) grew on either unenriched seawater from the collection site or basal synthetic seawater. Erdschreiber was a poorer medium for the isolation of algae than seawater alone. Few algal colonies grew on either marine nutrient agar or trypticase soy agar. Nitrite inhibited algal growth. Media enriched with thiamine, biotin, or nitrate, phosphate, and B12were stimulatory. Soil extract or an acetone extract ofEnteromorphatripled growth; a complex vitamin mixture, or glycerol, or mannitol, or an autoclaved extract ofEnteromorphadoubled colony numbers. The greatest numbers of diatom types (43) and total colonies (655) were recovered on media enriched with acetone extract ofEnteromorpha, suggesting a possible nutritional relationship betweenEnteromorphaand its epiphytes.The representativeness of the isolations from the natural community as a function of time was also considered. Concentrations of selected dissolved potential growth‐stimulating nutrients were measured within and external toEnteromorphacommunities. We conclude that the algal assemblage growing epiphytically onEnteromorpha intestinalishas a diverse auxotrophic profile which contributes to the productivity and stability within this important component of the epiphytic community and that much of the organic substrates used by individual species originate within and are recycled among the community members.
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Jan 1, 1976
René Le Cohu 
