Instantaneous benthic response to different organic matter quality: In situ experiments in the Benguela Upwelling System

Abstract

The benthic community in continental slope and deep-sea sediments of the Benguela Upwelling System was supplied with ¹³C-labelled organic matter (OM) of two different qualities using a benthic chamber lander. Freeze-dried cultures of Skeletonema costatum served as ‘fresh’ OM. ‘Altered’ OM of the same material had been additionally dialysed to remove low-molecular weight compounds. In order to investigate the benthic response pattern, mineralization of labelled OM, uptake by macrofauna and incorporation into bacteria were followed over 18–36 h. Total oxygen uptake was not affected beyond natural variation by the OM addition. Mineralization dominated the ¹³C-labelled phytodetritus processing, constituting 71–95% of the total processed OM. Bacterial incorporation of phytodetrital carbon exceeded macrofaunal uptake at all stations. Stations situated in a major centre of OM deposition showed phytodetritus processing rates on average twice as high as outside the depocentre. Phytodetritus processing was 1.5, 2.5 and 4.3 times higher for fresh than for altered OM at 605, 1019 and 1335 m water depth, respectively. Our observations clearly indicate the importance of OM quality on mineralization rates.

Keywords:

• Benguela Upwelling System
• benthic chamber lander
• 13C labelling
• deep-sea sediments
• mineralization
• OM quality

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Acknowledgements

The authors wish to thank J. Langreder and A. Nordhausen for the technical handling of the lander, R. Krammer for LECO measurements, M. Shovitri and A. Schramm for help with the fatty acid analysis. The captain and crew of the R/V Meteor are thanked for their assistance in obtaining high-quality samples. We are particularly indebted to S. I. Bühring for her patient support on any topic and in any situation. The constructive comments of two anonymous reviewers and the editor are gratefully acknowledged. The writing of this manuscript was supported by the Baltic Sea Research Institute Warnemünde (‘Come back to research’ grant). This work was funded by the Max-Planck-Society and the Deutsche Forschungsgemeinschaft as part of the DFG-Research Center ‘Ocean Margins’ of the University of Bremen (no. RCOM0512).

Notes

Published in collaboration with the University of Bergen and the Institute of Marine Research, Norway, and the Marine Biological Laboratory, University of Copenhagen, Denmark

Additional information

Notes on contributors

Ursula Witte

Present address: University of Aberdeen, Aberdeen AB24 2TZ, UK