Tracer Experiments in Feeding Littoral Foraminifera*†‡

Abstract

SYNOPSIS. Tracer technic has proved to be an excellent tool in the study of predator‐prey relationships among the foraminifera. More than fifty axenic species of protists including diatoms, dinoflagellates, chlorophytes, chrysophytes, cyanophytes, bacteria and yeasts were tested as potential food for Allogromia sp (NF), A. laticollaris, Am. monia beccarii, Quinqueloculina spp, Rosalina floridana, Anomalina sp, Elphidium sp, Spiroloculina hyalina, Globigerina bulloides , and Globorotalia truncatulinoides. Although many types of potential food are present in the environment, foraminifera select only certain organisms. The yeasts, cyanophytes, dinoflagellates, chrysophytes and most bacteria tested were not eaten. Selected species of diatoms, chlorophytes and bacteria were eaten in large quantity. Three additional factors affect feeding: the “age” of the food organism, the “age” of the foraminifer or its position in the life cycle, and the concentration of the food. Feeding by foraminifera on most food is erratic below a concentration of 10 3 organisms and is approximately directly proportional to concentration within a range of 10 3 ‐10 6 organisms per 10 ml experimental tube. A natural bloom of Protelphidium tisburyensis was analyzed. A high concentration of 6 species of diatoms characterized the community. A “bloom”‐feeder hypothesis for foraminiferal nutrition is presented.