engleski

Quantitative variability of the copepod assemblages in the northern Adriatic Sea from 1993 to 1997

Quantitative variability of the copepod assemblages in the northern Adriatic Sea were investigated at two stations, during 43 cruises, from January 1993 to October 1997. Samples were taken at 0.5, 10, and 20 meters, as well as near the bottom, using five-litre Niskin bottles. For inter-annual variation in the density of copepod assemblages data were presented as total number of nauplii and copepodites with adult copepods of following groups: Calanoida, Cyclopoida-oithonids, Cyclopoida-oncaeids and Harpacticoida. Moreover, hydrographic conditions, both fractions of phytoplankton, nonloricate ciliates and tintinnids were taken in considerations. Nauplii are the most numerous fraction at both stations with an average over 74% in the total number of all copepod groups. Their number were significantly higher at western eutrophic station, while at the eastern oligotrophic station, an absolute maximum of 693 ind.l-1 was noted. The maximum values of calanoids and oithonids occur generally during summer and always more numerous at the western station 33 to 50% and 50 to 63% respectively. The most abundant taxa identified were calanoid Paracalanus parvus and cyclopoid Oithona nana. Oncaeid species Oncaea waldemari and Monothula subtilis dominated during late autumn and winter. An atypical increase abundances of oncaeids during the summer of 1997, could be related to an invasion and mass occurrence of the calycophoran siphonophore Muggiaea atlantica. It can be concluded that these dominant copepods are responsible for the stabilization of very complex processes. Atypical appearances of major copepod groups and disturbances in the copepod population structure itself can significantly influence changes in the ecosystem of this very sensitive region.

phytoplankton ; zooplankton ; copepods ; Adriatic ; northern Adriatic

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