Distribution of Calanus spp. as determined using a genetic identification system

Abstract

The morphological similarity of Calanus species necessitates that the only unambiguous way of discriminating between the different species at any developmental stage is with molecular tools. We have developed a simple molecular technique to distinguish between the four species of Calanus copepods found in the North Atlantic (Calanus helgolandicus, C. finmarchicus, C. glacialis and C. hyperboreus) at any life stage. This system involves the PCR amplification of a region of the 16S rRNA gene, followed by Restriction Fragment Length Polymorphism (RFLP) analysis of the amplified product. This paper describes the application of the technique to a number of Calanus samples taken from a wide geographical range within the North Atlantic. Samples were acquired from sites ranging in latitude from the English Channel (50°N) to Tromsø (69°N), including many regions of co-occurrence. A comparison has been made between the distribution of Calanus as determined by molecular techniques and distributions established using traditional morphological identification. The molecular analysis has clearly shown extended areas of distribution and co-occurrence and has confirmed the intraspecific conservation of the restriction sites and therefore the reliability of the technique.