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Title: The density and biomass of mesozooplankton and ichthyoplankton in the Negro and the Amazon Rivers during the rainy season: The ecological importance of the confluence boundary
Authors: Nakajima, Ryota
Rimachi, Elvis V.
Santos-Silva, Edinaldo Nelson
Calixto, Laura S.F.
Leite, Rosseval Galdino
Khen, Adi
Yamane, Tetsuo
Mazeroll, Anthony I.
Inuma, Jomber C.
Utumi, Erika Y.K.
Tanaka, Akira
Keywords: Chlorophyll A
Organic Carbon
Organic Nitrogen
Arthropod Larva
Cell Density
Chlorophyll Content
Controlled Study
Dry Weight
Environmental Factor
Predation Risk
River Basin
River Ecosystem
Ultraviolet Spectroscopy
Water Temperature
Issue Date: 2017
metadata.dc.publisher.journal: PeerJ
metadata.dc.relation.ispartof: Volume 2017, Número 5
Abstract: The boundary zone between two different hydrological regimes is often a biologically enriched environment with distinct planktonic communities. In the center of the Amazon River basin, muddy white water of the Amazon River meets with black water of the Negro River, creating a conspicuous visible boundary spanning over 10kmalong the Amazon River. Here, we tested the hypothesis that the confluence boundary between the white and black water rivers concentrates prey and is used as a feeding habitat for consumers by investigating the density, biomass and distribution of mesozooplankton and ichthyoplankton communities across the two rivers during the rainy season. Our results show that mean mesozooplankton density (2,730 inds. m-3) and biomass (4.8 mg m-33) were higher in the black-water river compared to the white-water river (959 inds. m-33; 2.4 mg m-33); however an exceptionally high mesozooplankton density was not observed in the confluence boundary. Nonetheless we found the highest density of ichthyoplankton in the confluence boundary (9.7 inds. m-3), being up to 9-fold higher than in adjacent rivers. The confluence between white and black waters is sandwiched by both environments with low (white water) and high (black water) zooplankton concentrations and by both environments with low (white water) and high (black water) predation pressures for fish larvae, and may function as a boundary layer that offers benefits of both high prey concentrations and low predation risk. This forms a plausible explanation for the high density of ichthyoplankton in the confluence zone of black and white water rivers. © 2017 Nakajima et al.
metadata.dc.identifier.doi: 10.7717/peerj.3308
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