Oxygen dynamics in choanosomal sponge explants

Abstract

Oxygen microprofiles were measured over the boundary layer and into the tissue of 10-day-old cultivated tissue fragments (explants of 2–4 cm³) from the choanosome of the cold-water sponge Geodia barretti with oxygen-sensitive Clark-type microelectrodes. At this time of cultivation, the surface tissue and the aquiferous system of the explants is regenerating, which makes oxygen and nutrient supply by pumping activity impossible. Oxygen profiles showed a parabolic shape, indicating oxygen flux over a diffusive boundary layer and into the tissue. Oxygen was always depleted only 1 mm below the sponge surface, leaving the major part of the explants anoxic. Diffusive oxygen flux into the explant was calculated from three oxygen profiles using Fick's first law of diffusion and revealed 9 μmol O₂ cm⁻³ day⁻¹, which is in the lower range of in situ oxygen consumption of whole sponges. The ability of G. barretti to handle continuous tissue anoxia enables choanosomal explants to survive the critical first weeks of cultivation without a functional aquiferous system, when oxygen is supplied to the sponge explant by molecular diffusion over its surface.

Keywords:

• Geodia barretti
• microelectrodes
• oxygen consumption
• oxygen profiles
• sponge cultivation

Acknowledgments

Thanks are due to the crew of R/V Hans Brattström and the Marine Biological Station of Bergen University. Access to these installations has been supported by the IHP (Improving Human Research Potential) Programme from the European Union through contract no. HPRI-CT-1999-00056. This paper represents publication no. 42 of the research programme BOSMAN (03F0358A and C). Financial support was provided by the Bundesministerium für Bildung und Forschung (BMBF), Germany. We thank Wolfgang Dröse for the preparation of histological sponge sections, and Andreas Reimer for assistance with flux calculations.