Lake Ohrid and Lake Prespa biological parameters

The phytoplankton were collected by a 5-liter Ruttner sampler, and preserved in 4% formalin and the counting and identification was done according to Utermohl (1958) under the inverted microscope LW101-2.
Concentration of chlorophyll a was determined by spectrophotometry following its extraction in 90% ethanol (ISO 10260,1992

Meyns et al., 1994).

The zooplankton were collected by a 5-liter Ruttner sampler in pelagic zone and dredge in littoral zone, filtered in situ through a sieve (45?m mesh-size) and preserved in 4% formalin. The specimens were qualitatively and quantitatively analysed under a Laica DM IRB microscope (100 to 600× magnification) and Olympus BX43 microscope (100 to 1000× magnification) .

Macrozoobenthos was sampled using van Veen grab (225 and 400 cm3). Species have been identified using Wild Heerburgg binocular (10 to 60× magnification)

Macrophyte vegetation - A Van Veen grab and a "spider" grab were used for sampling. The samples were packed in polyethylene bags and fixed in 4% formalin.

Fish population sampling was done according to the European Standard CEN 14757 ? standardized protocol