Distribuição horizontal nictemeral de Cladóceros (CRUSTACEA: BRANCHIOPODA) em um lago de águas pretas do baixo Rio Negro (Lago Tupé, Manaus, Amazonas).

Abstract

In tropical regions the fluctuations in biotic and abiotic components of a lake can be observed within the diel cycle which makes the metabolism of these ecosystems peculiar. The understanding of horizontal movements by cladocerans, along the day at different seasons and the mechanisms of such phenomenon will generate relevant information regarding these organisms population dynamics, which will improve the knowledge on the behavior of cladocerans in black water environments, as well as assist improvement in methodology and sampling of this community in future studes. This paper proposes to study the horizontal distribution of cladocerans in three consecutive diel cycles, comparing high and low water periods (June and November/2011, respectively) at Tupé lake (and Amazonian black water lake). The Tupé lake is connected to the Negro river only by a narrow channel that allows input and output of water according to the season. The water temperature ranged higher when comparing times of the day, in opposition to places of sampling during both sampling periods - high water (23,8 ºC to 27,3 ºC) and low water (22 º to 27º C). Temperature decreased as sampling took place further from the margins. Higher values of dissolved oxygen (4,14 mgO2/L) and total pigments (0,65 μg/L) were registered in the low water period, but no spatial and temporal patterns were observed. Suspended material showed similar values in both sampling periods, also without general patterns. A total of 16 taxa of cladocerans were recorded. Species richness was higher during the night water period, while adundance and density were higher during the low water period. Bosminopsis deitersi and Ceriodaphnia rigaudi accounted for about 78% of the abundance of cladocerans. During the high water sampling period, a variation in the average density of cladocerans between first hours of day (02, 06 and 10 am) was observed, with higher population density at 06am. Significant difference in cladoceran abundances were observed only during the high water period, both spatially (p = 0.043) and temporally (p = 0.009). The Principal Component Analysis (PCA) showed that two components explained 84% of accumulated variation and seem to indicate, respectively, the spatial and temporal variation. A discrete distinction between day (06, 10, 14) and night (18, 22, 02) and between sampling places close to the inshore (L1, L5) and sampling places close to the offshore (L2, L3, L4) was observed and indicates the existence of a pattern of distribution influenced by temporal, and most importantly, spatial conditions. Some taxa showed preference for certain sampled places. The Canonical Correlation Analysis (CCA) showed the formation of four groups: group 1, sampling places close to the offshore (L2, L3, L4); group 2, sampling places close to the inshore (L1, L5); group 3, night samples (6 pm, 10pm, 02am) and group 4, day samples (06am, 10am, 02pm). A clear pattern of distribution was observed for 5 taxa, and that allows us to speculate about patterns in horizontal distribution.