Diet and growth rates of Meganyctiphanes norvegica in autumn

Abstract

Fatty acid biomarkers analysis was performed on juvenile and adult northern krill (Meganyctiphanes norvegica) to determine variability in diet between individuals and the consequences for their growth rates. Animals were sampled from Gullmarsfjorden, western Sweden during September 2004 and incubated for 4 days to measure instantaneous growth rate (IGR) before subsequent fatty acid analysis. We found positive linear relationships between IGR and certain fatty acid concentrations within adult specimens. In particular, highest growth was seen in individuals containing high concentrations of 18:2(n-6) and 18:3(n-6), indicative of filamentous algae and/or terrestrial carbon dietary sources, and 16:4(n-1), a biomarker fatty acid for diatoms. Similar relationships were not evident for juvenile krill. In an accompanying study, stomach content analyses established that adult krill had been feeding on a diverse range of red, brown and green benthic filamentous algae, which contain fatty acids of the (n-6) series. Incidence of filamentous algae in the stomachs of juvenile krill was much lower, possibly reflecting the shallower water depths inhabited by this maturity stage. Although a benthic feeding mode has previously been observed for M. norvegica, this is the first direct evidence to indicate that benthic food sources can be important in supporting the growth of this euphausiid. Furthermore, high variability in growth rates and fatty acid concentrations between individuals suggest a diversity of feeding strategies within this fjordic population.

Keywords:

• Meganyctiphanes norvegica
• growth rates
• filamentous algae
• fatty acid trophic markers

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

We thank Mike Thorndyke, scientists and staff of Kristineberg Marine Research Station for their welcome and support. Bo Bergström, Matilda Haraldsson and the master and crew of MV ‘Arne Teselius’ ably assisted our work. The Royal Swedish Academy of Sciences is thanked for their invitation to GT and IE to undertake the research. The project was supported by a grant from the European Commission 6th Framework Programme on ‘Research Technological Development and Demonstration: Access to Research Infrastructure programme’. DP, GT and KS carried out this work as part of the FLEXICON project of the DISCOVERY 2010 programme at the British Antarctic Survey.

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