Depth integrated water samples were taken from 20 ponds near Bratina Island on the McMurdo Ice Shelf and 6 ponds from Cape Bird to characterise the planktonic community structure of the ponds and to determine species interactions, in particular the effects of microzooplankton grazing. Water samples were analysed for species abundance, chlorophyll a, nitrogen (DON, NO3, NH4), phosphorus (DRP, DOP), ... conductivity, temperature and pH. Ponds near Bratina Island were resampled 3 weeks later to determine the stability of the plankton community structure and to examine variations in structure with water depth. Species were identified/quantified by microscopical analysis (fluorescent microscopy used to enumerate bacteria, autotrophic picoplankton and microprotozoa). Four experiements were conducted to determine potential food sources for microzooplankton and to assess whether microzooplankton control phytoplankton populations through grazing or nutrient regeneration including 1) in situ enclosures to monitor changes in chlorophyll a, bacteria, picoplankton and flagellates over 5 days, 2) fluorescent beads and fluorescent labelled algae used as tracer particles for feeding investigations, 3) in situ enclosures to determine the effects of the rotifer on bacteria and phytoplankton abundance and 4) the rotifer Philodina gregaria was analysed for pigment analysis to discriminate between different food sources. The causes of light attenuation in 40 melt ponds near Bratina Island were examined with concentrations of chlorophyll a, inorganic suspended solids and dissolved yellow substances in the ponds and horizontal black disc sighting range measured.