RFLP procedure to discriminate between Clausocalanus Giesbrecht, 1888 (Copepoda, Calanoida) species in the Central Cantabrian Sea

Traditionally, zooplankton studies have been carried out on larger species and later developmental stages, at least in the case of copepods. This fact is due to the difficulty of distinguishing between all the morphologically very similar species and genus, especially at immature stages. Nowadays, however molecular techniques allow us to discriminate these species easily. We have developed a RFLP (Restriction Fragment Length Polymorphism) technique to distinguish between the species of the genus Clausocalanus which are present at our study zone, the Central Cantabrian Sea. This genus belongs to the “small” fraction of mesozooplankton (500–200 μm), and it has been scarcely studied even though it is an important component of the mesozooplankton. This technique allows identification of individuals and from small body parts.