title: Oxygen dynamics and transport in the Mediterranean spongeAplysina aerophoba.
abstract: The Mediterranean spongeAplysina aerophobakept in aquaria or cultivation tanks can stop pumping for several hours or even days. To investigate changes in the chemical microenvironments, we measured oxygen profiles over the surface and into the tissue of pumping and non-pumpingA. aerophobaspecimens with Clark-type oxygen microelectrodes (tip diameters 18-30 μm). Total oxygen consumption rates of whole sponges were measured in closed chambers. These rates were used to back-calculate the oxygen distribution in a finite-element model. Combining direct measurements with calculations of diffusive flux and modeling revealed that the tissue of non-pumping sponges turns anoxic within 15 min, with the exception of a 1 mm surface layer where oxygen intrudes due to molecular diffusion over the sponge surface. Molecular diffusion is the only transport mechanism for oxygen into non-pumping sponges, which allows total oxygen consumption rates of 6-12 μmol cm-3sponge day-1. Sponges of different sizes had similar diffusional uptake rates, which is explained by their similar surface/volume ratios. In pumping sponges, oxygen consumption rates were between 22 and 37 μmol cm-3sponge day-1, and the entire tissue was oxygenated. Combining different approaches of direct oxygen measurement in living sponges with a dynamic model, we can show that tissue anoxia is a direct function of the pumping behavior. The sponge-microbe system ofA. aerophobathus has the possibility to switch actively between aerobic and anaerobic metabolism by stopping the water flow for more than 15 min. These periods of anoxia will greatly influence physiological variety and activity of the sponge microbes. Detailed knowledge about the varying chemical microenvironments in sponges will help to develop protocols to cultivate sponge-associated microbial lineages and improve our understanding of the sponge-microbe-system.
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Friederike
authors.initials: F
authors.lastname: Hoffmann
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany ; Center for Geomicrobiology, Department of Biological Sciences, University of Århus, Ny Munkegade 1540, 0800 Århus C, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Røy
authors.affiliation: Research Center for Infectious Diseases, University of Würzburg, 97070 Würzburg, Germany.
authors.forename: Kristina
authors.initials: K
authors.lastname: Bayer
authors.affiliation: Research Center for Infectious Diseases, University of Würzburg, 97070 Würzburg, Germany.
authors.forename: Ute
authors.initials: U
authors.lastname: Hentschel
authors.affiliation: Biologisches Institut, Abteilung Zoologie, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Pfannkuchen
authors.affiliation: Biologisches Institut, Abteilung Zoologie, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany.
authors.forename: Franz
authors.initials: F
authors.lastname: Brümmer
authors.affiliation: Max Planck Institute for Marine Microbiology, Celsiusstr. 1, 28359 Bremen, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: de Beer