Potential misidentifications of two climate indicator species of the marine arctic ecosystem: Calanus glacialis and C. finmarchicus

T M Gabrielsen,J Berge,D Vogedes,B Merkel,J E Søreide,E Johansson-Karlsson,A Bailey,Ø Varpe,H Nygård

doi:10.1007/s00300-012-1202-7

Abstract

Calanoid copepods of the genus Calanus represent an important, nutrient-rich food source for a multitude of Arctic marine organisms. Although morphologically very similar, their life histories and ecological roles differ. Because the distribution of Calanus glacialis and C. finmarchicus corresponds to Arctic and Atlantic water masses, respectively, they are regularly used as climate indicators. A correct identification of these species is therefore necessary in many ecological, environmental and climatological studies. In this study, we aimed at validating the traditionally used morphological characteristics (combining prosome length and copepodite stage) for separation of species of Calanus by using molecular tools (PCR–RFLP of the 16S mtDNA). A total of 418 specimens of copepodite stages CIV, CV and CVI(af) from three Arctic fjords have been identified both morphologically and genetically. We find that the morphological identification systematically overestimates the abundance of C. finmarchicus at the expense of C. glacialis. Hence, parts of the C. glacialis populations are found to be structurally smaller and the within population size range thus larger than previously assumed. Consequently, using the traditional morphological species delimitation poses a serious problem in the use of these two species as indicators of Atlantic versus Arctic water masses and thus as climatic indicators. Furthermore, it obscures our understanding of the life history differences between the two species and of their relative importance as food for a number of ecologically and economically important species in the Arctic.

Highlights

Calanoid copepods of the genus Calanus represent an important, nutrient-rich food source for a multitude of Arctic marine organisms
We find that the morphological identification systematically overestimates the abundance of C. finmarchicus at the expense of C. glacialis
Our analyses show that C. glacialis is frequently misidentified as C. finmarchicus when the species delimitation is based solely on prosome length (Table 1; Fig. 2)

Summary

Introduction

Calanoid copepods of the genus Calanus represent an important, nutrient-rich food source for a multitude of Arctic marine organisms. Berge Faculty of Biosciences, Fisheries and Economics, University of Tromsø, 9037 Tromsø, Norway indicators of Atlantic versus Arctic water masses and as climatic indicators It obscures our understanding of the life history differences between the two species and of their relative importance as food for a number of ecologically and economically important species in the Arctic. Calanus spp. dominate the biomass of the mesozooplankton community by up to 75–90 % in Arctic and sub-Arctic seas (Mumm et al 1999; Hays et al 2005; Wassmann et al 2006; Blachowiak-Samolyk et al 2008), and these herbivores represent an energy-rich food source of fundamental importance for a number of ecologically and commercially important species such as polar cod (e.g. Lønne and Gulliksen 1989; Renaud et al 2012), little auk (Steen et al 2007; Karnovsky et al 2008), bowhead whales (Weslawski et al 2000) and for large pelagic fish stocks of the subArctic North Atlantic (Varpe et al 2005). The smaller C. glacialis Jaschnov is an Arctic shelf species, whereas the smallest C. finmarchicus Gunnerus is an Atlantic species that occurs in the Arctic closely associated with the distribution of Atlantic water (Jaschnov 1970; Daase et al 2007; Søreide et al 2008)

Methods

Results

Conclusion