Zooplankton seasonal dynamics in the neighbouring lakes Takvatn and Lombola (Northern Norway)

The zooplankton of two neighbouring lakes, situated in northern Norway (69 degrees 07'N), was studied during the ice-free season of 1994. Zooplankton structure and seasonal dynamics are compared, and the importance of biotic interactions and seasonality (temperature and photoperiod) as determinants of the observed patterns is evaluated in light of collected data and previous knowledge of the systems. The main events in zooplankton seasonal succession were restricted to the short period of stratification and were similar in the two lakes. Basin morphometry and biota are considered for explaining the marked between-lakes difference in community structure: Daphnia dominates in the shallow lake Lombola, where brown trout (Salmo trutta L.) is most represented; while rotifers and the copepods Eudiaptomus graciloides (Lilljeborg) and Cyclops scutifer Sars dominate in Takvatn, where Arctic charr (Salvelinus alpinus (L.)) has the hegemony of the pelagic.