TROPHIC ACTIVITY OF PLANKTONIC-FORAMINIFERA

Light and electron microscopic examination of eight species of spinose and six species of non-spinose planktonic foraminifera show that all of them with the possible exception of Hastigerina pelagica are omnivorous. H. pelagica may be exclusively carnivorous or prey very infrequently on phytoplankton. Electron-microscopic examination of food vacuoles indicated that diatoms and dinoflagellates are among the more common algae consumed, but some species of planktonic foraminifera also prey upon other eukaryotic algae. Laboratory studies on survival of selected species of planktonic foraminifera in relation to food type and frequency of feeding show that Globorotalia truncatulinoides survived best when offered a diet of the coccolithophorid Emiliania huxleyi as compared to a diatom or dionoflagellate unialgal diet. Moreover, longest survival in laboratory culture as a function of feeding interval occurred when G. truncatulinoides was fed every 3 days compared with a daily or 12-day interval, and that H. pelagica survived longest when fed every 1-3 days. The diversity of prey accepted by planktonic foraminifera, their ability to survive for extended periods without food, and a moderate predation pressure based on laboratory feeding experiments may help to explain their abundance and geographical diversity. © 1979, Marine Biological Association of the United Kingdom. All rights reserved.