Effects of phosphorus supply on phagotrophy by the mixotrophic alga Uroglena americana (Chrysophyceae)

Abstract

The mixotrophic alga Uroglena americana forms a dense 'bloom' in Lake Biwa, Japan, in spring when dissolved inorganic phosphorus is in short supply relative to the requirements for algal growth. To assess the possibility that this alga uses bacteria as a substitutable P source via phagotrophy, feeding experiments were conducted using bacteria-sized fluorescent microspheres as tracer particles. The exper~rnents revealed that the ingestion rate of U. americana on the food particles (bacteria + mcrospheres) is significantly affected by the concentrations of phosphate as well as food particles