Community structure of crustacean zooplankton in subarctic ponds — effects of altitude and physical heterogeneity

Crustacean zooplankton (Cladocera. Copepoda) distribution patterns, community composition and response to altitude, temperature, pH and surface area were studied in 17 fishless subarctic ponds in the Kilpisjärvi area, NW Finnish Lapland. Despite their harshness, the ponds harboured diverse groups of zooplankton Altogether 50 species were found from ice-out in June-August 1994. There was both a marked decline in the species number and a change in the composition of pond communities with increasing altitude and decreasing temperature as well as decreasing pH. Pond surface area was least significant in determining the species composition Ponds at low elevations harboured up to 21 species while the fell top ponds usually had > 10 species. Chydoridaen cladocerans were the most dominant group even though their number greatly diminished in ponds above the timber line.