The distribution, abundance and ecology of mixotrophic algae in marine and freshwater plankton communities

Abstract

Abstract : Mixotrophic algae are algae that combine photosynthesis with phagotrophy to satisfy nutritional requirements. Mixotrophic algae have been found to dominate the nanoplankton assemblage in some aquatic environments, and algal phagotrophy can account for a significant fraction of total bacterivory on occasion. The distribution and abundance of mixotrophic algae have not been widely characterized, however, and the factors that control their abundances and phagotrophic activity in aquatic environments are poorly understood. The vertical distribution and abundance of mixotrophic nanoplankton was therefore documented in a variety of aquatic environments including the oligotrophic open ocean (Sargasso Sea), nine freshwater seepage ponds (Adirondack Mountains, NY) and three coastal salt ponds (Falmouth, MA) using epifluorescence microscopy and fluorescently labeled prey to trace ingestion by algae. Field experiments designed to examine the influence of prey density, nutrient availability and light intensity on mixotrophic nanoplankton abundances and their phagotrophic activity were also carried out to examine the adaptive significance of phagotrophy for mixotrophic algae in surface waters of the Sargasso Sea and in the epilimnion of one freshwater seepage pond.