Feeding-related controls on microbial nitrogen cycling associated with the Arctic marine copepod Calanus hyperboreus

P Stief,Tg Nielsen,Rn Glud,Asb Lundgaard

doi:10.3354/meps12700

Abstract

Feeding-related controls on microbial nitrogen cycling associated with the Arctic marine copepod Calanus hyperboreus

Highlights

The zooplankton community in Arctic marine ecosystems is dominated by the co-occurring calanoid copepod species Calanus hyperboreus, C. glacialis, and C. finmarchicus (Hirche 1991, Madsen et al 2001)
The copepod-associated microbial N-cycling itself was clearly dominated by denitrification with activities ~20-fold higher than nitrification, dissimilatory nitrate reduction to ammonium (DNRA), dissimilatory nitrate reduction to nitrite (DNRN), and net N2O release
The patterns of O2 and N-turnover associated with freshly released (≤12 h) fecal pellets resembled the patterns observed for algae-fed copepods, except for the complete absence of net NH4+ release and nitrification activity

Summary

Introduction

The zooplankton community in Arctic marine ecosystems is dominated by the co-occurring calanoid copepod species Calanus hyperboreus, C. glacialis, and C. finmarchicus (Hirche 1991, Madsen et al 2001). Sinking carcasses of diverse copepod species from different aquatic ecosystems displayed significant anaerobic N-cycling (Glud et al 2015, Stief et al 2017, 2018). In small marine and freshwater copepod carcasses, dissimilatory nitrate reduction to ammonium (DNRA) and dissimilatory nitrate reduction to nitrite (DNRN) appear to be important anaerobic N-cycle pathways (Stief et al 2017, 2018). These 2 pathways do not directly contribute to fixed-nitrogen loss. Fixed-nitrogen loss coupled to pelagic microsites is commonly overlooked by incubation-based rate measurements due to pre-filtration of water samples or small incubation volumes that exclude the presence of copepods, fecal pellets, and phytodetritus aggregates. By taking into account the fixed-nitrogen loss coupled to copepods and other pelagic microsites, the models of oceanic nitrogen dynamics might be considerably improved, especially for low-oxygen environments (Bianchi et al 2018)

Methods

Results

Discussion

Conclusion