This investigation of Pomeranian Bay waters was conducted from March 2001 to August of 2003 from aboard the r/v Nawigator XXI, which is owned by the Maritime Academy in Szczecin. A total of 147 water samples were collected at 15 stations on three transects in the Pomeranian Bay from Świnoujście, Międzyzdroje, and Dziwnów to the Odra Bank. Zooplankton was sampled with a Bongo type planktonometer Ø = 20 cm with a mesh size of 80 μm during 10 min. filtering hauls in the pelagic zone from the bottom to the surface at an average vessel speed of 3 - 4 knots. The method developed and published by Orłowski was used to transform the large amount of seasonal data for the entire study period into isoline illustrations of the spatial structures in the Pomeranian Bay of mesozooplankton and selected species, namely Acartia bifilosa, Acartia longiremis, Pseudocalanus elongatus, and Temora longicornis. The average mesozooplankton aggregations in ten consecutive seasons at the 15 stations investigated from 2001 to 2003 in the entire Odra estuary area fluctuated from 2,442 to 92,200 ind. m-3. The highest species variety was noted among marine Copepoda, which was the dominant group in virtually every season investigated. Their maximum abundance reached as much as 213,493 ind. m-3. The euryhaline species A. bifilosa occurred throughout the research period and at all stations at an abundance that reached 210,443 ind. m-3. The seasonal succession series were as follows: in spring, the dominants were Acartia spp. and Evadne nordmanni; in summer - Keratella cochlearis, Bosmina coregoni maritima, and A. bifilosa; in fall - T. longicornis and Acartia spp.; in winter - T. longicornis and Centropages hamatus.
