Diel vertical distribution, and herbivory of copepods in the south-western part of the Black Sea

The abundance and population structure of copepods were studied in the southwestern part of the Black Sea in May 1994, April and September 1995, April, June and September 1996. Vertical distribution and diel vertical migration of copepods were studied in April and September 1995 and June 1996. In addition, the grazing rates of three size classes of copepods—300–500, 500–1000 and 1000–2000 μm—were estimated in September 1995. The total abundance of copepods was higher in June samples due to the large contribution of the warm water species, Paracalanus parvus. Vertical distribution appeared to be related to season, species, stages of species and the oxygen concentration in the water column. Female, copepodite V (CV) and copepodite IV (CIV) stages of Calanus euxinus and female Pseudocalanus elongatus showed strong diel vertical migration from the surface waters to the oxygen minimum zone (OMZ). Copepodite stage V of C. euxinus showed seasonal migration, and was observed in diapaused phase at the OMZ in June and in September samplings. The large (1000–2000 μm) and medium (500–1000 μm) fractions of copepods had maximum gut fluorescence at night. Total grazing represented 32% of daily total integrated primary production. Phytoplankton carbon ingested met all three fractions of the basic metabolic requirements of the copepod community in the Black Sea.