On Antarctic shelves, glass sponges (Porifera, Hexactinellida) dominate the megabenthic epifauna. But in spite of intensive research on epifauna community structure, process studies on the ecophysiology of key species are so far lacking, due to the difficulty of accessing glass sponges in their habitat and keeping them alive for experimental work. Here, we present preliminary results of an in situ study carried out in the Weddell Sea using a remotely operated vehicle (ROV) to measure feeding, respiration, ammonium excretion and silicate uptake in the common glass sponges Rossella nuda / Anoxycalyx joubini, R. racovitzae and R. villosa. A custom-developed ROV-mounted water sampler was successfully deployed. A total of 22 samples from sponge oscula and 21 samples from ambient waters were analyzed for picoplankton, ammonium and dissolved silicate concentrations. Optode measurements in the ambient water and inside the sponge oscula revealed a measurable difference of ~0.5 µM oxygen between ambient and exhalant waters. Together with estimates of the exhalant volume flow from concomitant fluorescein dye experiments, the oxygen and silicon uptake as well as the ammonium excretion of individual sponges can be estimated. Our findings will help elucidate the role of hexactinellid sponges in carbon and silicon cycling and contribute to understanding future effects of sea-ice and productivity changes on Antarctic ecosystem structure, functioning and services.