Bacterivory by mixoplanktonic phytoflagellates

GEREA, M.; UNREIN, F.

Cardiff

Congreso; International Conference on Mixoplankton; 2021

Cardiff University

Mixoplanktivory in algae, defined as the combination of phagotrophy and phototrophy in a single cell, is widespread among most algal groups containing flagellate species. Phytoflagellates vary widely in their ingestion capability and response to the abiotic conditions. Here, we used literature data to review the ecological strategy and impact on bacterioplankton of the different algal groups. We extracted information from about 50 articles, including marine and freshwater systems, resulting in more than 600 measurement of grazing rates from natural communities. In addition, we summarised results of experiments performed with isolated strains. Chrysophyceae are the most ?heterotrophic algae?, with three times higher grazing rates than any other algal class, and a significant impact on bacterioplankton. Dictyochophyceae (Pseudopedinella) has grazing rates comparable to Chrysophyceae, however its low abundance results in a lower impact. Ingestion rates of these phytoflagellates are correlated with bacterial abundance, a typical functional response of ?primary heterotrophic? organisms. Haptophyceae are moderate grazers, while Cryptophyceae seems to be the least heterotrophic phytoflagellate. Despite its lower grazing rate, Cryptophyceae can account for a significant percentage of the total bacterivory during period of high abundance. Dinoflagellates are important bacterivores, however because of their cell-size they usually prefer larger preys, and bacteria contribute little to their carbon budget. In situ measurements of Prasinophyceae and Raphidophyceae are scarce and precluded a clear characterization of these groups. As a general rule, the addition of nutrient have a negative effect, or no effect, on the grazing rates of all the groups. Contrarily, the effect of light on grazing rates is not straightforward and it seems to be more species-specific dependent.