Diel vertical migration of Cladocera in a compartment of a tropical reservoir

Erika dos Santos Silva


Aim: This study aimed to analyze the nycthemeral variation in the vertical distribution of Cladocera populations, in a compartment of Furnas hydroelectric plant reservoir. The area is along a segment of Sapucaí River (21º22’16” S and 46º00’06” W), in Minas Gerais state, Brazil. In addition, this study aimed to check for a consistent vertical migration pattern among species, and their relationship with physical and chemical properties of the water. Methods: Samplings were carried out every three hours, from 10:00 am of January 15 to 10:00 am of January 16, 2014. These samples were taken at five depths, from the surface to the near-bottom layer (0, 2, 4, 6, 8, and 9 m). Results: Water column thermal and chemical stratifications and thermocline occurrences were registered in the middle of the day. Among the registered Cladocera species, only Ceriodaphnia cornuta and C. silvestrii displayed a significant migration pattern, which was mainly related to chlorophyll-a and dissolved oxygen concentrations. Feeding at high temperatures in the surface layer and assimilating at lower ones in depth usually confer metabolic advantages to the vertically migratory species, besides the fact that nycthemeral migration is an effective strategy against visual predators. Other cladocerans, such as Diaphanosoma species, are always found at high densities near the surface and low ones in depth, which might be because of oxygen depletion at deeper layers, thus acting as a limiting factor.  For other species, with less locomotory capacity, thermal and chemical stratifications can act as barriers to migration and distribution through the water column. Conclusions: In this study, a well-defined pattern of vertical migration was found for two Cladocera species and its possible causes were hypothesized.  This pattern may probably be found for zooplankton species in other segments of Furnas reservoir, with similar physical and chemical properties.


Variation nycthemeral, zooplankton, Furnas, stratification

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