Oxygen dynamics and flow patterns of Dysidea avara (Porifera: Demospongiae)

Abstract

The present publication presents oxygen properties and pumping behaviour of Dysidea avara. Oxygen profiles were measured near and inside the atrial space of the osculum with a Clark-type micro-electrode. Pumping sponges had profiles with oxygen concentrations marginally lower than that of the aquarium water. In contrast, diffusive profiles, with a clear boundary layer above the sponge surface, and oxygen penetrating only 0.5 mm into the sponge tissue, were typically that of a sponge which was not pumping. Diffusive oxygen flux at the sponge surface was 4.2 μmol O₂ cm² d¹ and the calculated volumetric filtration rate was 0.3 cm³ water cm³ sponge min¹. The oxygen concentration in the osculum was temporally fluctuating between 95 and 59% saturation at a frequency of approximately once per minute. The combination of static oxygen micro-electrode measurements and particle tracking velocimetry (PTV) allowed us to simultaneously observe fine-scale oxygen fluxes and oscular flow patterns in active sponges, even at extremely low pumping rates. Oscular oxygen concentration and flow were correlated but not always synchronous to the second. Particle tracking velocimetry was used to visualize the flow field around the sponge and to distinguish sponge-generated flow from the unidirectional current in a flow-cell.