SOME ECOLOGICAL RELATIONSHIPS BETWEEN PHYTO- AND ZOOPLANKTON

¹ Hopkins Marine Station of Stanford University, Pacific Grove, California

1. Several planktonic algae from the brines of the sea water evaporation ponds were fed to the brine shrimp Artemia. They were found to differ in their nutritive value to this filter-feeding animal. One of these algae, Stichococcus sp., could not be utilized by the animal as a food source.

2. Controlled experiments of the effect of filter-feeding Artemia and Tigriopus on a mixed population of two unicellular algae indicate that the animals are capable of acting as differential grazers; The heavy bloom of Stichococcus in the evaporation ponds could be due to the effect of preferential digestion of competing algae by grazing animals.