Seasonal and diel changes in the vertical distribution in relation to the age structure of Microcalanus pygmaeus Sars and Ctenocalanus citer Bowman and Heron, (Pseudocalanidae, Copepoda) from Croker Passage (Antarctic Peninsula)

The development of two representatives of Pseudocalanidae and the nature of their population distribution in the water column were investigated on the basis of plankton samples collected over three seasons in night-day series in Croker Passage. The investigations showed that the two species begin reproducing in different seasons. Regardless of season, the growth of M. pygmaeus is more advanced than that of C. citer. Both species are characterised by a separation of their populations in the water column. The youngest copepodite stages (I–III) inhabit the upper portion of the water in which the given species occurs, while the oldest specimens, especially males, inhabit the deepest waters. Additionally, the first growth phases (CI–CIII) show a tendency to concentrate closer to the surface at night.