Genetic differentiation and local temporal stability of population structure in the euphausiid Meganyctiphanes norvegica

Meganyctiphanes norvegica (M. Sars 1856), the northern krill, is the largest and most abundant euphausiid species in the northern hemisphere, where it represents a key component of many pelagic communities. Although planktonic, krill could be considered a nektonic organism, as it is capable of active movements. This behaviour may be adaptive, because it allows these organisms to maintain their geographic position, leading to stable population structure, despite being continuously exposed to the heterogeneous oceanic conditions. By means of single-strand conformation polymorphism and DNA sequencing, we analyzed allelic variation of the Subunit 1 of NADH dehydrogenase mtDNA locus in 23 populations of the northern krill Meganyctiphanes norvegica, from 15 locations spanning the distribution range of the species. Analysis of the data indicated that the genetic structure, as revealed by analysis of population samples collected at the same site in consecutive years, was stable during that sampling period. Our results revealed the existence of 4 genetically and geographically distinct gene pools of M. norvegica, 2 occurring in the NE Atlantic ('northern' NE Atlantic and 'southern' NE Atlantic), 1 in the NW Atlantic, and 1 in the Mediterranean (Ligurian) Sea.