Zooplankton abundance in the Aliakmon River, Greece

The zooplankton of the River Aliakmon was studied from February 1995 to January 1996 at two sampling stations. Seventy nine different taxa were recorded, including a possible new species (Pleurotrocha n.sp.). The zooplankton community was dominated by rotifers, which made up to 96\% of the total abundance. The two stations differed in terms of abundance (p <0.05) and species composition. Upstream, abundance was less than 1131 ind m(-3), while it varied from 712 to 13870 ind m(-3) downstream. The highest zooplankton densities were recorded in autumn but no seasonal pattern was observed. Water temperature, dissolved oxygen and the nitrogen and phosphorus nutrients were the main environmental parameters which were found to influence zooplankton abundance in the Aliakmon.