Vertical and temporal distribution of two copepod species, Cyclops scutifer and Diaptomus pribilofensis, in 24 h arctic daylight.

Factors structuring zooplankton communities in areas with 24 h of sunlight are not well understood. In stratified temperate lakes with fish, zooplankton generally undergo a diel vertical migration (DVM) to avoid predation. Zooplankton abundance may also be linked to the quality and quantity of food. To explore factors that determine vertical structure of zooplankton where DVM does not occur, we obtained time-series data on the vertical distribution of the two dominate copepods, Cyclops scutifer and Diaptomus pribilofensis, in Toolik Lake, Alaska, a site within the Arctic Long Term Ecological Research area. These two species compose ∼80–90% of pelagic mesozooplankton community density. Temperature plays a large role in the vertical distribution of these two species. During the summers of 2002 and 2003, C. scutifer underwent a seasonal vertical migration from the epilimnion to the hypolimnion as water temperatures increased. Diaptomus pribilofensis exhibited a strong preference for warmer water and were not present in the water column until epilimnetic temperatures reached ∼9°C. During both years of this study, C. scutifer and D. pribilofensis segregated vertically in the water column along thermal gradients when the two species overlapped temporally. [ABSTRACT FROM AUTHOR]