Effects of light, dissolved nutrients and prey on ingestion and growth of a newly identified mixotrophic alga, Chrysolepidomonas dendrolepidota (Chrysophyceae)

Chrysolepidomonas dendrolepidota was described recently and little is known of its distribution, physiology or ecology. Although many photosynthetic chrysophytes have been identified as mixotrophic, combining photosynthesis and phagotrophy, this study provides the first evidence of mixotrophic nutrition in C. dendrolepidota. In a 2 × 2 factorial experiment with relatively high and low levels of light and nutrients, the ingestion rate was highest in the high-light, low-nutrient treatment. Growth rates and abundance increased in high- versus low-light conditions. In additional experiments with nitrogen and phosphorus modified separately, ingestion rate was different from the control only in the treatment with both macronutrients reduced. Supplementing low-nutrient treatments with additional bacteria led to an increase in algal abundance relative to controls without added bacteria. These results indicate that acquisition of major nutrients is a likely driver of mixotrophic nutrition in C. dendrolepidota. Although the distribution of C. dendrolepidota is unknown, mixotrophic chrysophytes can seasonally dominate planktonic algal abundance in some aquatic systems, and nutrient limitation is known to increase bacterivory in some of those species. Identifying and understanding how different mixotrophic species respond to changing environmental cues is crucial to understanding their roles in aquatic food webs.