Abstract
The aim of this study was to identify patterns of vertical distribution of planktonic cladocerean populations throughout the diel cycle, during the low and high water periods, and its ecological implications for a black water Amazonian lake. Tupe Lake is a black water lake located near the Brazilian city of Manaus. A channel links the lake with the Negro River and its flood pulse. This study was performed in a low-water period (November 2005) and in a high-water period (June 2006). Samples were taken on a 24-hour cycle, every 4 hours and at each meter of the water column, using a Schindler-Patalas trap equipped with a 55µm size mesh. A total of 16 species were registered during the low water period, wherein Bosminopsis deitersi, Moina minuta, and Ceriodaphnia cornuta were the most abundant species. B. deitersi migrated to the bottom during the afternoon, while M. minuta, Moina reticulata, and Holopedium amazonicum remained at the bottom for the entire diel cycle. During the high-water period, a total of 18 species were observed, and B. deitersi, C. cornuta, and Diaphanosoma polyspina were the most abundant species. During both sampling periods, no pattern was detected for C. cornuta. Generally, vertical patterns of distribution were less evident in the high water period, due to the mixing of the lake.
Highlights
Zooplankton populations are distributed heterogeneously throughout an ecosystem and, as previously reported by Pinel-Alloul (1995), they usually exploit the environment in patches
Bosminopsis deitersi and Moina minuta were the most abundant species, followed by Ceriodaphnia cornuta (20%) and Diaphanosoma polyspina (15%); these species represented more than 90% of the counted organisms
There was a difference in the composition of planktonic cladocereans between the low and high water periods
Summary
Zooplankton populations are distributed heterogeneously throughout an ecosystem and, as previously reported by Pinel-Alloul (1995), they usually exploit the environment in patches. In tropical lakes, this heterogeneity generally occurs seasonally in a spatial-temporal scale and daily in a verticalhorizontal scale. Zaret and Suffern (1976) explained vertical migration as a mechanism of zooplankton to avoid predation, which is related to luminosity, body size and visibility of the prey These factors cause predators like planktivorous fish to prey differently on the Cladocera community (Zaret, 1972; Zaret and Kerfoot, 1975). Lampert (1989) pointed to light-related mortality as the ultimate reason for the vertical movements
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